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  1. #1
    Jon mackay's Avatar
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    Default From gable vents to Ridge & Gable Vents

    Does anyone have any documentation on the impact of installing a ridge vent to a house that originally had only gable vents?
    There are no soffits.

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  2. #2
    Ted Menelly's Avatar
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    Default Re: From gable vents to Ridge & Gable Vents

    Quote Originally Posted by Jon mackay View Post
    Does anyone have any documentation on the impact of installing a ridge vent to a house that originally had only gable vents?
    There are no soffits.

    Just gable vents is not and has never been the way to go. I have always written this up as inadequate and expressed the point of adding some central roof top ventilation. The attic fills with hot air and slowly just from the rise of this heat makes its way to the gable ends. It is kind of like filling a bowl with water and the only course it has is to over flow the sides to escape. Adding ridge vents is like drilling holes in the bottom of that bowl and letting the water flow out.


  3. #3
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    Default Re: From gable vents to Ridge & Gable Vents

    Quote Originally Posted by Jon mackay View Post
    Does anyone have any documentation on the impact of installing a ridge vent to a house that originally had only gable vents?
    There are no soffits.
    Well, you can one or the other but not both. But, it sounds like this might be the only option to getting some airflow into this attic.

    How old is the home?

    Any pictures of the home showing why it does not have soffits and soffit vents?

    With all attic ventilation you need to have a low cooler source of air and then a higher vent to allow the air to escape.

    In the home you are asking about the gable vents will be acting as the low source and the ridge vent will be the high escape vent. I guess it is be better than nothing.

    Scott Patterson, ACI
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  4. #4
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    Default Re: From gable vents to Ridge & Gable Vents

    The only downside toadding more ventilation is the heat loss in colder months. More venting will suck more heat out of the house in the winter. So along with the recomendation for a cooler house you must also recommend upgrades to insulation and sealing practices to make the change work properly.


  5. #5
    chris mcintyre's Avatar
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    Default Re: From gable vents to Ridge & Gable Vents

    Quote Originally Posted by Jon mackay View Post
    Does anyone have any documentation on the impact of installing a ridge vent to a house that originally had only gable vents?
    There are no soffits.
    Jon, this may not be exactly what you are looking for, but is a good reference that I recently found for attic ventilation.

    http://www.airvent.com/pdf/literature/PAVbooklet.pdf


  6. #6
    Jon mackay's Avatar
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    Default Re: From gable vents to Ridge & Gable Vents

    The house was built in the late 50s.

    The thought is that with gable vents, there is an opportunity for a cross breeze to vent the attic space.
    When you add a ridge, the air becomes stagnate and actually reduces the ventilation. I'll try to get more info to see if this is a correct theory or not..


  7. #7
    David Bell's Avatar
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    Default Re: From gable vents to Ridge & Gable Vents

    Most of the gable only houses I see had,or have a whole house fan that sounds like a helicoptor in your hallway. I have had good luck with rooftop attic fans located about 2 feet down from the ridge,centered between the 2 vents, thermostatically controlled. This design gives the cooler outside air a chance to drop down letting the fan pull out the warmest air.


  8. #8
    Jon mackay's Avatar
    Jon mackay Guest

    Default Re: From gable vents to Ridge & Gable Vents

    Quote Originally Posted by David Bell View Post
    Most of the gable only houses I see had,or have a whole house fan that sounds like a helicoptor in your hallway. I have had good luck with rooftop attic fans located about 2 feet down from the ridge,centered between the 2 vents, thermostatically controlled. This design gives the cooler outside air a chance to drop down letting the fan pull out the warmest air.
    A problem with this method is that with the focus on energy efficiency, these are last resort methods. Thermostatically controlled attic fans can pull conditioned air from the living area into the attic and it does not provide ventilation in the winter so moisture build up becomes an issue.
    Whole hose fans are great in the summer to quickly cool your house but they do nothing for attic ventilation.


  9. #9
    Ted Menelly's Avatar
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    Default Re: From gable vents to Ridge & Gable Vents

    Quote Originally Posted by Jon mackay View Post
    The house was built in the late 50s.

    The thought is that with gable vents, there is an opportunity for a cross breeze to vent the attic space.
    When you add a ridge, the air becomes stagnate and actually reduces the ventilation. I'll try to get more info to see if this is a correct theory or not..

    Not true at all. With just gable vents and little air movement outside the air is stagnant. When ridge or turbine vents are added to the gable vents to break the attic up the air flow is much better.

    Cross breeze in the summer does not happen much on those still summer hot days. With a breeze it is much better but the ridge or turbine vents will do nothing but add to that flow. Even with eve vents this practice is much better. Even better than that when there is eve vents is to close off the gable vents and add ridge vents. Gable vents are old technology that was never very efficient in moving air.


  10. #10
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    Default Re: From gable vents to Ridge & Gable Vents

    Unless I missed it while reading the above posts, the unasked question was unanswered ... which kinda makes sense, doesn't it?

    When gable vents only are present, should one install ridge vents (which would provide a very limited improvement and upon which a determination for sizing can NOT be based) ... or ... should one install soffit vents (which would provide a very sizable improvement and upon which a determination for sizing can be based).

    Jerry Peck, Construction / Litigation Consultant
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  11. #11
    Jon mackay's Avatar
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    Default Re: From gable vents to Ridge & Gable Vents

    I suppose it is a little foggy, sorry.
    The question is: If there was gable vents originally and there is no soffit area that would allow for vents, should it be changed by adding a ridge vent?
    AND what would the effect of installing a ridge vent be? good or bad


  12. #12
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    Default Re: From gable vents to Ridge & Gable Vents

    Quote Originally Posted by Jon mackay View Post
    I suppose it is a little foggy, sorry.
    The question is: If there was gable vents originally and there is no soffit area that would allow for vents, should it be changed by adding a ridge vent?
    AND what would the effect of installing a ridge vent be? good or bad
    Post # 3 provided you with the answer.

    To properly vent an attic, you need a lower source of ventilation that will act like an intake. Then you need a higher vent source that will allow the warmer air to rise and exit. This design creates a stack or chimney effect in the attic. This is why soffit vents are so important.

    Scott Patterson, ACI
    Spring Hill, TN
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  13. #13
    Michael Kulikowski's Avatar
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    Default Re: From gable vents to Ridge & Gable Vents

    Adding a ridge vent to a house that only has gable end vents will help if the gable end vents are blocked off from the inside to prevent a "short circuit" of air flow from the gable to the ridge. Addinionally adding soffit vents will help considerably providing there is adequate air flow and not blocked by insulation.

    In many cases up here in the Rochester NY area there are houses with very small soffits or none at all. There are products that allow air flow to come from the eave when properly installed. One such prouduct is called "Smart Vent" SmartVent by DCI - The #1 Choice for Attic Intake Ventilation
    Hope this helps


  14. #14
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    Default Re: From gable vents to Ridge & Gable Vents

    Quote Originally Posted by Michael Kulikowski View Post
    Adding a ridge vent to a house that only has gable end vents will help if the gable end vents are blocked off from the inside to prevent a "short circuit" of air flow from the gable to the ridge. Addinionally adding soffit vents will help considerably providing there is adequate air flow and not blocked by insulation.

    In many cases up here in the Rochester NY area there are houses with very small soffits or none at all. There are products that allow air flow to come from the eave when properly installed. One such prouduct is called "Smart Vent" SmartVent by DCI - The #1 Choice for Attic Intake Ventilation
    Hope this helps
    If the home does not have soffit vents and you block the gable vents then the ridge vent will not do anything. You must have two sources of air.

    You are correct that the gable vents should be covered, but that is only if a lower air supply source is added. Like soffit vents, but if the design of the home does not allow for this the gable vents and ridge vent combo are better than nothing.

    Scott Patterson, ACI
    Spring Hill, TN
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  15. #15
    Jon mackay's Avatar
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    Default Re: From gable vents to Ridge & Gable Vents

    Ok, that makes sense.

    So the only time the "short circuit" comes into play is when there are soffit vents in the equation..

    Thank you for the info..


  16. #16
    Ben Liu's Avatar
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    Default Re: From gable vents to Ridge & Gable Vents

    Jon- you said there are no soffits, but what about eave venting? For instance, drilling two to three 2" diameter holes in the blocking between the rafters. This will provide your cool air intake.


  17. #17
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    Default Re: From gable vents to Ridge & Gable Vents

    Quote Originally Posted by Ben Liu View Post
    Jon- you said there are no soffits, but what about eave venting? For instance, drilling two to three 2" diameter holes in the blocking between the rafters. This will provide your cool air intake.
    Ben is getting there.

    Unless there is low venting to allow the air in, there are no calculations on what to base the amount of venting required.

    There are two methods of calculating venting area requirements: 1) ALL LOW VENTING (i.e., soffit vents, eave vents); 2) LOW AND high venting (i.e., soffit vents/eave vents AND ridge/gable/off ridge vents).

    The option missing from the calculations is NO LOW VENTING, of which you are describing.

    If you have gable vents and you add higher vents, will that help? Yes.
    - How much will it help? Don't know, no method to figure it out.
    - How much venting is needed? Don't know, no method to figure it out.

    Adding ridge vents to to gable only vents is like going to a barber shop and trimming a freshly cut crew cut ... you aren't doing much at all other than making a lot of noise with the electric clippers.

    Jerry Peck, Construction / Litigation Consultant
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  18. #18
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    Default Re: From gable vents to Ridge & Gable Vents

    Jerry, I hope you see this reply to this older thread. I was just reading it and was hoping you could answer a question I have. I am in a similar situation with an older home, 1940's cape bungalow, in which the original unfinished attic had gable vents which was given a new roof about 25 years ago with a ridge vent installed. The large louvered vents were replaced with a same sized double hung windows for additional lighting and fresh air when you're up in the attic; otherwise the windows are left closed. Insulation originally was originally in the floor joint, but when the ridge vent was put in, the old insulation was removed and insulation was placed, with an air gap, running the full length of the rafters. The house has no soffits.

    As ridge vents were relatively new on the market along with being young and dumb at the time, we had no idea this could be a problem. But reading online about other things, as led me to realize the faultiness of what was done 25 years ago. We are planning to rip down the old insulation that is running the rafters lengths to see if there are any issues there and we are hoping things are okay. Either way, the roof will need to be replaced soon anyway, given it's age, but we will have to wait a bit due to finances due to recently being reduced to one income.

    If we find things are okay for the short term wait of redoing the roof and we have not created crazy damage up there over the course of years, I am capable of installing temporary gable vents low down on the side outer walls of the attic. Is this better than nothing, or should we just roll new insulation between the floor joist (once the old ridge insulation is pulled out) until we can afford to have some sort of "SmartVent" type of vents installed when the roof gets done?

    At this point in time, there is no musty smell up there and our things stored up there seem fine, but we don't know what we will find when we pull down the old ridge insulation and want to be prepared with some sort of plan. Of course, we could just decide to keep our horse blinders on until it is time to replace the roof, but I'm not sure I want to do that. I'd rather know what it is I'm going to possibly be faced with. Any insight would be greatly appreciated.


  19. #19
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    Default Re: From gable vents to Ridge & Gable Vents

    This is what I understand you did, if I am reading it correctly:
    - You removed the insulation which was between the ceiling/floor joists in the attic. Doing so removed the thermal barrier between the interior living space and the outdoors.
    - You installed insulation on the underside of the roof between the rafters, but left a slot open for the ridge vent. While the ridge vent basically made that insulation useless, it would have been useless anyway due to not having insulated the gable end walls (you didn't say you insulated them, so I am presuming that you did not). What you accomplished was to basically make the house have no insulation along its top, is there any insulation in the walls? Being a house of that age, it is quite possible that there was no insulation in the walls either.

    I'm going to guess that your are spending a decent amount of money to heat and cool the house because it is, for all practical purposes, uninsulated.

    Being uninsulated may have saved you from having caused any problems with the house as the uninsulated house will breathe quite rapidly and the moisture generated inside the living space will, along with any heating or cooling, go right on through the walls and attic to the outdoors.

    Jerry Peck, Construction / Litigation Consultant
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  20. #20
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    Default Re: From gable vents to Ridge & Gable Vents

    Yep, pretty much; like I said, we were young and dumb. After reading your reply, I realized I had a few things mixed up, so I went back an looked at some old photos to get the proper sequence of events:

    -1981: purchased unimproved 1940 cape bungalow from original owner; a 750 sq. ft. 1-1/2 story with typical central hall with all rooms opening off of it. There is a kitchen, living room, dining room, bedroom, full-bathroom, unfinished attic, and unfinished basement. The house was pretty much the way it was built as the original owner never improved upon it. When we bought it, it even including a stove on feet, enamel slope sink as the kitchen sink with the counter being the metal cover that lays over the deep side sink along with an old round washing machine and coal bin in the basement. We could not afford much and actually thought we were in way over our heads at the time.

    -1984: We replaced pull down ladder to attic with a full-sized straight run stairs. We had built at a local mill and it was bought in via temporarily removing one of the old windows and it was installed by the miller. The miller also suggested we might want him to install a ridge vent for better ventilation given we were planning to eliminate the large louvered attic vents with double hung windows when the rest of the windows were being done. Our thinking was the windows would give some natural lighting to the attic and miller's thought was the ridge vent would do the job of the louvered vents. Ridge vents were pretty new at the time, we didn't know much about them, but it seemed to make sense, so we gave the green light.

    After this was done, later in 1984, we had all the old drafty windows in the house along with those large louvered attic vents replaced with thermal insulated windows. We then removed the old loose insulation that was laying in the ceiling/floor joist of the attic and then decided to insulated between the rafters (the full length) making sure not to push it in all the way. We using the rolled type of insulation with the foil backing. We also insulated the outer walls which I forgot to mention earlier. Having the windows available for extra light and extra fresh air during this process was a good thing. We also closed off the stairwell at the top with the old closet door that was removed to allow for the new stairs.

    -1986: we had the house vinyl sided in which ridged board insulation was placed over the old asphalt siding before the vinyl siding was hung.

    -1992: Twenty years ago this week, I found the entry in my old check registry, we had a new roof put on, so the roof is not 25 years old. The old roof was scrapped down to the tongue and grove roof decking and the ridge vent carefully removed and replaced after the new roof was put on. It is one of those aluminum surface mounted type that was available back in 1984.

    The roof actually still looks good with no curling or lifting and we have never had any leaking problems. We've even been through a few wicked hurricanes over the years; Irene devastating our neighborhood last year. The most that every happened to us was the ridge vent once became bit loose during a Nor'easter; it started to shake a little bit on the one end. So we shot lines over the house with a ball launcher (large slingshot) we use with our dogs. We then lash down that small section of ridge vent until the next day when it was nailed back down. Since, including Hurricane Irene, there has been no issues.

    So that's it. I see now we basically created an attic space with all the insulation lining it's outer shell but did not allow for any new air to be drawn in from the outside. So the ridge vents has been doing little to nothing all these years. I don't know what it was we were thinking of back then other then hot air rises so it would naturally go out the ridge vent, forgetting that duh...... air has to flow from someplace otherwise it's a dead air pocket.

    It is funny, I only stumbled upon this realization when looking for other information and fell upon various postings from people about proper attic ventilation and airflow. That's when the light bulb went on and I got one of those sinking feelings that we'd screwed up big time. We are hoping we will find the old roof decking is okay and we didn't cause a mold or rotting problem. But like I mentioned. The roof does look good from the ground and there is no smell in the attic and our things are in fine shape, so I'm hoping this is a good sign.

    You mentioned the utility bills. Interestingly enough we do not have gigantic bills and we still heat with the original gravity feed octopus coal converted to gas furnace located in the basement with one duct to each of the first floor rooms and a large return duct in the circular central hall. A few years back the utility company was offering free energy efficiency testing of existing furnaces, of which we participated. The guy who came had never seen anything like our "octopus" and was amazed when it came back with a 90+ percent efficiency rating. Not bad for old technology. So we were left with, if it ain't broke, don't fix.

    Anyway, our gas bill which includes heating, hot water heater, cooking and a clothes dryer is $78 per month. We are on budget billing. Our electric which includes lighting, appliances, some fans, a single window AC unit in our bedroom for those unbearable days, TV, computer, etc... is $80 per month. Compared to everyone else we know this is low. We do conserve energy and do not leave things on, but even so, there is only so much a person can do with what you are given. So at least, along these lines, what we did in the attic doesn't seem to have caused crazy utility bills.

    Whatever we find up there when we pull down the old insulation this fall, we want to correct the lack of air flow the best we can until the roof needs replacing. Given this, we are wondering if there is a way for us to use the existing ridge vent by reverting back to the original method of insulating the ceiling/floor joist of the attic and then could come up with a way for outside air to be drawn in until we have the roof done. At that point, we can look into having something like those SmartVents mentioned previously in this discussion. They seem like a good idea for a soffitless house using a ridge vent.

    Since writing to you, it dawned on me, we already have two double hung windows were the old louvered vents were. They are approximately 30"x36" and about 3 feet up from the attic floor. I know the lower sash is not as low as would be preferred, but it would not require my making holes in the house and siding to put in low vent, like I was thinking earlier. I'm thinking I can use the existing windows temporarily by leaving them cracked open to create airflow to each other and existing ridge vent - pretty much back to the original concept of the old louvered vents that were there.

    Given we have had little to no air movement for 28 years, I'm thinking this is a reasonable temporary measure - if the space is opened up and not insulated, it should allow for the old roof decking to breathe until we have the roof done. What do you think?


  21. #21
    zippet's Avatar
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    Default Re: From gable vents to Ridge & Gable Vents

    Since posting the last reply, we started wondering that if our idea above is okay as a temporary measure until the roof needs to be done, what should we do about the attic stairwell when we get to the point in which we are rolling out the new insulation into the existing attic ceiling/floor joist spaces.

    When the staircase was installed, one side was left open and the attic was closed off at the top with a door and two insulated triangular walls. The resulting ceiling above the stairwell was also insulated when we insulated all the rafters. The stairwell side was sheet rocked to finish off this enclosure.

    Given this, we do not know whether we should take this down when ripping down all the other old insulation and enclose the attic at the bottom or just leave the current stairwell as is for now. Any thoughts or suggestions are greatly appreciated. Thanks.


  22. #22
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    Default Re: From gable vents to Ridge & Gable Vents

    Quote Originally Posted by zippet View Post
    Given we have had little to no air movement for 28 years, I'm thinking this is a reasonable temporary measure - if the space is opened up and not insulated, it should allow for the old roof decking to breathe until we have the roof done. What do you think?
    There is a lot to reply to, but given that what you did wrong you did the wrong way (which is a good thing), and that everything seems to be okay as it has turned out, I'd leave it the way you have it.

    When you insulate the underside of the roof decking, fiberglass batt would not be what would be used, spray foam would be. However, because you did use fiberglass batts, and fiberglass batts are known air leakers, air and moisture have been allowed to migrate up and out through the fiberglass insulation and though the roof decking and roof covering.

    Granted, the ridge vent has likely not done much good, but I doubt that it has done much harm either. With your utility bills being so low (compared to what I am used to - you may want to compare them to friends and neighbors in similar houses so you can sort of determine if your costs are about the same, lower, or higher than other comparable houses in the same climate.

    If about the same or lower, maybe just leave it as it is, or maybe close up the ridge vent for an unvented and sealed attic effect, except that the unvented attic would have had spray foam insulation and the attic is likely not really sealed. Again, by default, maybe leave things alone - I'm not really sure what is the best for you.

    I do think it is good that you did the wrong things the wrong way, er, not good that you did the wrong things, but that when you did them you did them wrong ... if that makes sense?

    Jerry Peck, Construction / Litigation Consultant
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  23. #23
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    Default Re: From gable vents to Ridge & Gable Vents

    Quote Originally Posted by zippet View Post
    Given this, we do not know whether we should take this down when ripping down all the other old insulation and enclose the attic at the bottom or just leave the current stairwell as is for now. Any thoughts or suggestions are greatly appreciated. Thanks.
    After all this time, I'd be inclined to leave it has you have it.

    Let's see what others here say about it.

    Jerry Peck, Construction / Litigation Consultant
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  24. #24
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    Default Re: From gable vents to Ridge & Gable Vents

    Yeah, I get what you mean, what you say makes sense. Hopefully this is our saving grace. We are encouraged a bit by the fact our roof is 20 years old and doesn't show any signs of curling, the attic doesn't have an odor, and that our utility bills are low.

    Which by the way, are low for our area even though there are not many houses as small as ours left anymore to compare; we are a bit of an anomaly. But, if you make a proportional comparison by square footage, we have friends and families with insane utility bills with most of them having the latest and greatest in heating and cooling along with their houses being sealed tight. Go figure.

    You mentioned perhaps closing off the ridge vent. This has crossed our minds, but not from the angle of creating an unvented attic but from the angle of just reverting back to the original method of venting with ceiling/floor joist insulation. We're starting to wonder, if this might not be a bad idea since we don't have soffits anyway. We could use adjustable window vents in the lower sash sections of the windows to have them act like the original louvered vents.

    I'm not really sure, however, if this would be penny wise and pound foolish, given the roof will ultimately have to be done anyway. Maybe we would ultimately be better off to have something like those SmartVents installed since the roofers would be up there anyway. It's something we have to think about, which leads me to another possible wrinkle.

    Yesterday, when searching more about venting and such, I also got hits on plumbing venting and I started to read about the proper clearance of various vents. Once again, I had a sinking feeling. Our cast iron plumbing vent runs straight up from the basement, through the shared wide plumbing wall of the bathroom/kitchen, and then straight up through the attic and out the roof. It is probably about three feet down the roof from the ridge vent. Should the close proximity of our plumbing vent to the ridge have been a reason why we should not have had the ridge vent put in, in the first place?

    If so, then this would mean we should close up the ridge vent and reverting back to the original venting method by the way I suggested above. Alternatively, I guess, if we find we didn't damage the roof decking, we could vent with old fashion gable vents, since these, as with the adjustable window vents, would be far enough away from our plumbing vent. If having these two different types of vents near each other is not an issue, then we are still left with weighing out our options.

    Interestingly enough, when out walking the dogs last evening, I started to look up at roofs. I noticed many houses have ridge vents, not the old type we have but the type you really don't notice, as they kind of blend in with the roof. I also noticed many of these houses have vent pipes pretty high up on their roofs.

    So I don't know what this means - is it okay or did lots of other people unwittingly make the same mistake. So the side question becomes: is having our ridge vent that close to our plumbing vent yet another major screw up? Or, is it okay for the ridge vent to be that close our plumbing vent pipe?

    Once again, thanks a bunch; we do appreciate your help and hope to hear from you soon.


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    Default Re: From gable vents to Ridge & Gable Vents

    Quote Originally Posted by zippet View Post
    It is probably about three feet down the roof from the ridge vent. Should the close proximity of our plumbing vent to the ridge have been a reason why we should not have had the ridge vent put in, in the first place?

    So the side question becomes: is having our ridge vent that close to our plumbing vent yet another major screw up? Or, is it okay for the ridge vent to be that close our plumbing vent pipe?
    Well, the plumbing vent is a bit too close to the ridge vent, but many older homes had plumbing vents too close to other things. That does not mean that all of those plumbing vents need to be torn out and relocated, but that the codes evolved over the years and things have changed.

    Here is an example of the codes changing,
    - From the 1997 Standard Plumbing Code:
    - - P904.5 Location of vent terminal. An open vent terminal from a drainage system shall not be located directly beneath any door, openable window, or other air intake opening of the building or of an adjacent building, and any such vent terminal shall not be within 10 feet (3048 mm) horizontally of such an opening unless it is at least 2 feet (610 mm) above the top of such opening.

    Note that the plumbing vent terminal was not allowed to be directly below any building opening (which includes attic vents), and that if the vent was within 10 feet horizontally of an opening, the vent had to be 2 feet above the opening.

    - Now from the 2009 IRC:
    - - P3103.5 Location of vent terminal. An open vent terminal from a drainage system shall not be located less than 4 feet (1219 mm) directly beneath any door, openable window, or other air intake opening of the building or of an adjacent building, nor shall any such vent terminal be within 10 feet (3048 mm) horizontally of such an opening unless it is at least 2 feet (610 mm) above the top of such opening.

    Note that the plumbing vent terminal is now allowed to be 4 feet directly below the opening that it was not allowed to be "directly below" before, so 4 feet must be sufficient air space between the vent terminal and the opening, however, the code also says that if the vent terminal is within 10 feet horizontally of such opening, that the vent must still be 2 feet above such opening.

    Okay, if we take "within 10 feet horizontally" to mean "horizontally", that would not allow the vent terminal to be within 10 feet *horizontally* of the sides of the window, but ... but the code now says that the vent terminal is allowed to be 4 feet below the opening, so now *horizontally* means down to 4 feet below the window, and it also means up to 2 feet above the window.

    Your vent terminal is 3 feet below such opening (the ridge vent) ... yeah, the ridge vent should not have been installed within that 4 foot clearance, except that there was no 4 foot clearance when you put that ridge vent in. The clearance was "directly below", and a vent terminal "directly below" but 15 feet down "directly below" the vent would not have been allowed back then, which is kinda silly when they allow it at 4 feet below.

    That said, there were codes which were even more specific on the location of a vent terminal:
    - 4610.1 Vent Terminals:
    - - (a) Extensions of vent pipes through a roof shall be terminated at least six inches above the finished roofing excluding base flashing, but not less than 4" above the invert of the emergency overflow.
    - - (b) Vent stacks on the exterior walls of a structure with parapet walls shall extend six inches above same. Vent extensions above the roof shall not exceed ten feet and be securely fastened to prevent wind damage. Where roofs are used for sun decks, solariums or similar purposes, all vents shall extend not less than seven feet above the deck.
    - - (c) Flag Poling: Vent terminals shall not be used for the purpose of flag poling, TV aerials, or similar purposes.
    - - (d) Roof Terminal:
    - - - (1) The roof terminal of any vent pipe if within 10 feet of any door, window or exhaust opening shall extend not less than three feet above such door, window or exhaust opening.
    - - - (2) The vent terminal of a sanitary system of a building shall not be located less than 10 feet developed distance from any mechanical air intake opening.
    - - - - EXCEPTION: Vent to exhaust separations as stated above shall not apply if all three of the following conditions exist:
    - - - - - 1. The vent opening is not within three feet (3') of the roof terminal of any exhaust.
    - - - - - 2. The vent system serves only a single family residential use, (i.e. Condominium, Apartment Building, Townhouse, Duplex or Single-Family Residence.)
    - - - - - 3. The roof terminal of the vent pipes and exhaust openings are through a sloped roof (2-1/2 in 12 or greater.)

    Note that the above code is 10 feet away from an any mechanical air intake opening, which excludes gravity vents, unless all three conditions are met - which includes not within 3 feet of any exhaust opening. Also, the vent much be at least 10 feet from "any door, window or exhaust opening" unless it is 3 feet above the opening.

    Should the ridge vent be there? Not really, but the codes sound like they do not agree on how far away it should be.

    Jerry Peck, Construction / Litigation Consultant
    Construction Litigation Consultants, LLC ( www.ConstructionLitigationConsultants.com )
    www.AskCodeMan.com

  26. #26
    Darrel Hood's Avatar
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    Default Re: From gable vents to Ridge & Gable Vents

    As Jerry showed, the codes are confused and contradictory. So experience and judgement, which some of these folks disparage take over. To start with, both the ridge vent and the plumbing vent are exhausts. So what are the possible negative effects?


  27. #27
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    Default Re: From gable vents to Ridge & Gable Vents

    After reading all of the above a few times, it is obvious how confusing things can get with changing standards.

    We noticed the reference to mechanical and gravity vents. Since none of our vents have mechanisms effecting their function, are we correct to assume this means all of our vents are gravity?

    Next, we think we understand that ridge vents are exhaust vents by nature as they are supposed to release hot air from between the rafters; but, we thought roof plumbing pipe vents were intake vents because we thought they sucked air in when water drains out. We most have something wrong here, given the last reply that states otherwise.

    Reading through the codes also made us realize we needed more precise measurements; so up we went. As you will see, my original guesstimate of 3 feet between vents was way off. We also measured our chimney, yet another opening to contend with. Our findings are:
    • Ridge vent is level with plumbing vent opening and they are only 19 inches apart;
    • Chimney opening is 2 feet above both the ridge and plumbing vents' horizontal planes;
    • The chimney opening is 5 feet diagonally from the ridge vent and 7-3/4 feet diagonally from the plumbing vent opening;
    • Horizontally, the chimney's mid-line is 4-1/2 feet from the ridge vent and 7-2/3 feet from the plumbing vent;
    • Our roof has a pitch ratio of 7:12.


    The 1997 and 2007 standards suggest we are horizontally non-compliant between the plumbing and ridge vents, as they are less than 10 feet apart with their openings being level to each other. However, these two code also specify the word intake in regards to air openings other than doors and windows in relationship to open vent terminals from drainage systems. Given this, we are thinking this means 'air exhaust openings' are okay, since it is not stated otherwise. If so, provided we are correct that ridge vents are exhaust vents, perhaps this means these 1997 and 2007 standards do not apply in our situation. Does this make any sense? If not, where are we going wrong?

    In regards to the relationship between our vent pipe and our chimney opening, which are original 1940 issue, we are thinking this is okay for two reasons. First, it was probably compliant back in 1940; and second, we think it is okay by the current standards because we are three for three in regards to the exceptions listed within the section specifically relating to roof terminal vent locations. Our pipe vent is not within 3 feet of the chimney opening, we are a single family residential dwelling, and the slope of our roof is greater than a 2-1/2:12 pitch. Does this also make sense? If not, again, where are we going wrong?

    Please let us know if our thinking is flawed; and if not, might it be possible we are compliant after all. Once again thanks a bunch.


  28. #28
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    Default Re: From gable vents to Ridge & Gable Vents

    I made a mistake in my words. You are right the plumbing vent intakes air in most of its functions. However, it does not take air into the living envelope. Therefore, I still wonder what are the possible negative effects if they are in close proximity?


  29. #29
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    Default Re: From gable vents to Ridge & Gable Vents

    Off the top of my head, the one issue that comes to mind is the potential for sewer gas to siphon into the attic space. Plumbing vents work in both directions allowing air when needed and constantly releasing sewer gas. Ridge vents can allow air in, thus you could end up with the plumbing vent dumping sewer gas (moist air) into the attic space.

    I suppose, you could have an attic furnace nearby that might cause other issues/concerns.



  30. #30
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    Default Re: From gable vents to Ridge & Gable Vents

    What you say makes sense and it is better to be safe then sorry, even if there is a possibility of wiggle room regarding the codes above. As a side note, all our attic is used for is to store the things we have accumulated over the past 33 years. There are no utilities up there other than a single light switch and outlet. It was my searching for ideas to how better to utilize the attic space that had me stumbling upon various discussions which made me realize we probably screwed up many years ago.

    This, however, does not negate your point about the possible infiltration of methane gas into the house. It wouldn't mix well with our gas stove in the kitchen nor gravity feed "octopus" of a furnace in the basement. As a side note, not that this makes a difference, we also have a sewer vent located low on the outside front wall of the foundation just above where our sewer line heads out to the street. It is one of those flush mounted round 6" iron plates with all the small holes.

    Anyway, given, all the points above, it seems like when it comes time to have the roof done again, it might be best to have the ridge vent removed, the decking closed up, and just revert back to the simple gable venting system that once was. If we go the route of taking the ridge vent out of the picture, we are assuming our original issue 1940 chiminey and roof pipe vent are okay, even though they are horizontally within 10 feet of each other with the pipe vent opening 2 feet below the chimney opening - correct?

    If so, we would next need to consider how to best handle the fact we swapped out the two louvered attic vents with double hung windows, all those years ago. We did this for some natural light and some extra fresh air. We are guessing it would be okay to use adjustable louvered window vent inserts (the type that fit into open window sashes) as our "gable" vents. If so, we are wondering if it would it still be a good idea to have SmartVents installed to increase air flow up there or just leave well enough alone.

    Would this plan be okay or is it also problematic? Thanks once again for any input.


  31. #31
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    Default Re: From gable vents to Ridge & Gable Vents

    The problem you have here is that you are not letting air into the building envelope, so having the vents to close is not a true code violation. The ridge vents are to allow moisture and air to escape, so it is really more of a good design to not have these two close together. The intent of the ridge vent is to exhaust air, but they can let air in, which is why I made my comment of ďyou couldĒ have... Kind of like a refrigerator and an oven in your kitchen, you can have them side-by-side, itís legal, but a bad design, they fight each other a bit, but it works.

    Iím only familiar with WI Codes and do not know the exact layout of your roof, but WI requires 10 feet horizontally or 2 feet above roof scuttles, doors, and openable windows, which doesn't really cover ridge vents. WI code allows a plumbing vent to terminate under vented soffit (overhang) when itís more than 5 feet below, or past the edge of the soffit, which gets us closer to a ridge vent. Using this logic you could be as close as 5 feet or be higher then the ridge as methane is lighter than air. You could also stop the ridge vent short when it gets within 5 feet of the plumbing vent.

    The chimney is higher than the plumbing vent and itís more than 5 feet away, I would not worry about it, and you would be compliant.

    In re-reading the posts you mention no soffit vents and others made the comment that the ridge venting is not doing much of anything as there is no air movement. The gable vents would have allowed some cross ventilation to occur. It also seems like you created a pseudo conditioned attic space that would not require venting, not legal in WI the way yours is done, but nonetheless is working in a similar way.

    Without seeing what you have I cannot really say what the best route is at this time. If your utility bills are fair, there is no evidence of moisture, and no odd odors Iím tempted to say ďleave well enough aloneĒ and worry about it when one of these guys inspect it when you decide to sellÖ lol.


  32. #32
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    Default Re: From gable vents to Ridge & Gable Vents

    Thanks for your thoughts and sorry for the delayed reply; we were away for a few days.

    We have much to think over and really won't know what we are up against until we pull down the old insulation. After all is said and done, it would be ice if we could continue to use the attic as conditioned storage space. If not, then we'll have to revert back to the way it once was with just insulation between the floor/ceiling joist.

    Given what everyone has said, it does seem we might be able to do this and not end up with the remaining vents too close. I sounds like we could close up the ridge vent and create a gable vented area above the collar beams as long as we put in something like SmartVents down low. We could insulate up the rafters, over and across at the collar beam level, and then back down the opposite side rafter.

    By doing so, we'd still have an attic within the conditioned air space and not have to worry about the stairwell and door or the first floor ceiling fixtures. Our attic 'ceiling' will end up lower then it is now, but that's okay, as the rafters would be vented properly.

    The vents should also end up be okay too, since we'll just end up with only our original chimney and plumbing vent up on the roof with the elimination of the ridge vent. And, even though the new gable vents will be a little be higher then the original louvered vents, that shouldn't be a problem.

    We are thinking this might work and at this point in life, we have no plans of going anywhere. We just want to fix the mess we created and hopefully the roof deck is okay. The thought of moving and starting all over again with who knows what, is not appealing.

    Does our idea sound like a feasible plan that might work?


  33. #33
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    Default Re: From gable vents to Ridge & Gable Vents

    Attached is a quick simple drawing with two options, but check with the AHJ (Authority Having Jurisdiction) if it is possible. Iím not sure you will get enough air flow with just the gable vents if you put up walls, like the drawing shows (or without walls), as you still need the soffit venting. Otherwise, I think, you will just create a wind tunnel above the collar ties and no real air movement at the bottom of the rafters.

    Attached Files Attached Files

  34. #34
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    Default Re: From gable vents to Ridge & Gable Vents

    Thanks for the drawings and whatever we go with, we will look into what is allowed. Meanwhile, since we don't have knee walls now, we figured we'd just continue without them. So we were thinking of doing what you illustrated in the second picture. I didn't even know the third was an option, but I guess it makes sense that if there is no air pocket to heat up then the roof decking should be fine; but I think that spray foam stuff is expensive and not really a DIY project. If we did end up doing this, could we put sheet rock up? Or people don't do that when they use that stuff? We don't have any sheet rock now, but if that would allow for putting up sheet rock, it is an intriguing method.

    With your first two drawings, you indicate needing soffits. Our house does not have soffits; the roof ends right at the edge of the house with a gutter attached directly there. This is why, when I read post #13, with that SmartVent product link, that seemed like a great idea for houses without soffits that need venting from down low. If we install those at the base of each rafter and used gable vents, would that create enough air flow up the rafters to the space above the collar ties and then out the gable vents on either end of the attic? Of would we still end up with a wind tunnel, even if we install something like those SmartVents down low?


  35. #35
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    Default Re: From gable vents to Ridge & Gable Vents

    You donít have to use spray foam, you could use Dowís Styrofoam and cut it into strips to place between the rafters and foam any gaps. By WI code you would have to cover the foam insulation with a thermal barrier, so yes, you can use sheet rock, at least in WI. The insulation you use canít allow air flow, and spray foam is the fast and easy way, but not the only way. Again, you will have to check with the AHJ. Different parts of the US can have big price swings, what might be cheap here can be expensive there.

    The lack of soffit venting, not soffit, is your problem. Even with the smart vents you are not getting air flow from the bottom to the top of the roof. The ridge vent acts (one of the ways) like a siphon, as the wind blows across the top it pulls air up from the low sides of the roof. But, you have to have vents at the bottom of the roof to make this happen. If you look at page 1 (fig. 1) and page 6 (fig. 9) of the manual from post 13 SmartVent by DCI - The #1 Choice for Attic Intake Ventilation you will see what Iím talking about, air in air out. Without seeing what you have I canít say what you can or canít do, but it sounds like you canít add soffit vents.


  36. #36
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    Default Re: From gable vents to Ridge & Gable Vents

    As intriguing as the whole spray foam idea is, it is probably not the route we'll be take. At this point, the roof still looks good from the ground. If, though, when we pull down the old insulation, we find the underside of the roof decking is a mess, this could change things. As we'd have to hire a contractor to fix the decking, it couldn't hurt to ask what it would cost to have them do the spray foam insulation as a finishing touch - since they'd be hear anyway, provided of course it is allowed and they actually do this sort of work.

    We are, however, hoping this is not the case and we are hoping we'll be able to just re-insulate using the rolled, foil backed insulation - just do it right this time. Since our house is not conducive to adding soffit vents, I took another look at the SmartVent link again, as you suggested. I then realized I was using the product name in conjunction with only one of the many different ways of applying their product, as if the two were synonymous. Which I now realize is not the case.

    What we were thinking of doing is to use their product using the eave application method, as it is shown for houses that do not have soffits. We are thinking, wiith the SmartVents installed in this way, that would be our 'air in' with our 'air out' being the gable vents located up high, once the ridge vent is closed up, which wouldn't happen until the roof needed to be done.

    Just as wind across a ridge vent is designed to get air moving, wouldn't the air flowing between the gable vents through the tunnel above the collar ties also get the air moving in such a way that it would draw air up from the SmartVents? Plus, as heated air rises, now that we will have put in SmartVents along the drip edge to prevent dead air pockets, wouldn't this, too, cause a sucking of air in from the bottom and ultimately out at the top?

    Have we got the 'air in' and 'air out' flow correct?


  37. #37
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    Default Re: From gable vents to Ridge & Gable Vents

    Yup, that will work, I was actually going to recommend that very idea of using a roof mounted eave vent. You will just have to maintain an air gap between the insulation and the decking. The ridge vent would be the best option as it pulls air up to the highest point, the gable vents would be the second choice, just not the best, but that could be argued. Bottom line, you are going to get air movement, and more than you have now.


  38. #38
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    Default Re: From gable vents to Ridge & Gable Vents

    I'm glad we are finally get a grasp on how things work. I noticed you used the phrase 'roof mounted eave vent' and I'm assuming this is the generic term for any sort of vent system that would vent the eave space, such as the eave application of the SmartVents. If I'm understanding your generic term correctly, I'll have to Google this to see what the various options are available out there to chose from. Maybe there are some types more suited for DIYers then other types.

    Which leads me to a side question. What did they do in the past? Capes date back to the 17th century when soffits weren't in the picture. It was also quite normal for people to use their attic spaces by typically adding knee walls and sloped ceilings to flat collar tie ceilings. Heck, that's how my siblings and I grew up. So, if gable vents were typically used for venting the peak space above the attic ceilings, what was used way back when to vent the air pocket space behind the knee walls? Just curious.


  39. #39
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    Default Re: From gable vents to Ridge & Gable Vents

    Quote Originally Posted by zippet View Post
    I'm glad we are finally get a grasp on how things work. I noticed you used the phrase 'roof mounted eave vent' and I'm assuming this is the generic term for any sort of vent system that would vent the eave space, such as the eave application of the SmartVents.
    When you add or keep the ventilation, you will be relocating the insulation from the underside of the roof decking down to being on the ceiling below the attic - right?

    As soon as you go with the insulation on the underside of the roof decking, regardless of what type, you will need to make sure to insulate the gable end walls and seal the attic (make the attic unvented).

    Which leads me to a side question. What did they do in the past? Capes date back to the 17th century when soffits weren't in the picture. It was also quite normal for people to use their attic spaces by typically adding knee walls and sloped ceilings to flat collar tie ceilings. Heck, that's how my siblings and I grew up. So, if gable vents were typically used for venting the peak space above the attic ceilings, what was used way back when to vent the air pocket space behind the knee walls? Just curious.
    Those older houses were built so 'loose' (with respect to air movement) that air and moisture would 'blow' right through the houses, that is what made those older houses "drafty" feeling. Newer construction is 'tighter' and has little air movement through the structure, some are so 'tight' that they required an intentional supply of fresh air from the outside through intake ducts/fans/heat exchangers. The heat exchangers typically work by routing the fresh air through a duct which is divided into two separate duct with a common wall, with either supply or return air through the other duct, that way the heat from the hotter air will transfer to the cooler air, making the fresh air being brought in closer to the temperature of the inside air, which then requires less heating or cooling to bring the fresh air to the desired temperature.

    Jerry Peck, Construction / Litigation Consultant
    Construction Litigation Consultants, LLC ( www.ConstructionLitigationConsultants.com )
    www.AskCodeMan.com

  40. #40
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    Default Re: From gable vents to Ridge & Gable Vents

    I'm not using anything fancy, it's just eaves refers to the low side of the roof and your vent would be on top of the roof. Most venting is located on the underside of the overhang, eaves, or soffit, which all kind of mean the same thing. What you show on the roof mount vent "SmartVent" is what I was referring to.


  41. #41
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    Default Re: From gable vents to Ridge & Gable Vents

    Michael Thomas
    Paragon Property Services Inc., Chicago IL
    http://paragoninspects.com

  42. #42
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    Default Re: From gable vents to Ridge & Gable Vents

    Hey all, thanks for all the input. I have a question about my side question. In my last posting, I asked about how eaves were vented in the past, meaning when there are no soffit vents and before newer SmartVent type of vents now available on the market. When I used the term eaves, I was referring to the empty space behind the knee wall of an attic bedroom, like I had growing up. The replies seem to suggest soffit and roof overhang areas are the eaves. If so, what is the air space behind a knee wall called? And, now that I've cleared up what space I was asking about, how did they used to vent this air pocket before SmartVents and such when there were no soffit vents?

    Meanwhile, we are hoping our 72 year old, soffitless, Cape Bungalow, was built loose enough to have allowed enough air movement to off set the possible damage we might have put into play 28 years ago. See Post #20 for those details. Even so, given everything, it seems like we have two problems to address: 1) the lack of airflow to the underside of our roofing deck, and 2) a ridge vent that is too close to our plumbing vent. Therefore, we are thinking the following is the best plan of attack.

    When we pull down the old insulation, we're thinking we will basically find either everything is okay, mild damage to the underside of the roof deck which can be fixed in place, or major damage in which it would make more sense to just have the entire roof ripped off and replaced. My gut is saying the last scenario is not likely because our 20 year old roof looks fine from the ground, we have no leaks, and there are no funky smells. Jerry also suggested we might have gotten lucky in this respect due to the age of the house. So, if this ends up being correct, we would like to proceed as follows.

    If we find minimal damage, we'll have the damage fixed and then allow the entire attic space to breathe for a bit before we do anything else. We need to do things in small financial steps, even if this means we will have to live with an empty unconditioned attic space with our stuff placed in the basement for a couple of years. If it is becomes the case, we would roll out batts of insulation, foil side down, between the floor/ceiling joist, much the way it originally was. We would then make use of the existing ridge vent (as we will not be at the point of having replaced the roof yet) and our two existing windows to supply ventilation to the now unconditioned attic space until we are ready to move on.

    If we get lucky and there is no damage and/or we are now ready to move on from the previous step, we would like to do the following. Have the ridge vent closed up (because it is too close to our plumbing vent) and replace it's function with two large triangular vents placed as high as they can go on the gable walls. Next we would install some form of lower venting system designed for houses that do not have soffits. After this, besides insulating the gable walls, we would use baffles between the rafters and insulate the rafters from their base up to the collar ties and across at this level to the other side and then back down to the base of the rafter on the other side. See the second drawing on the attachment post #33.

    Doing the attic this way, would give the rafters air-in from down low and air-out from up above through the gable vents at each end of the tunnel above the collar ties. And, since we will be using gable vents, which the house originally had, I also think this will eliminate the vent issue, as any of the newer type of vents we would be using will be way down along the drip edge of the roof. We're thinking this plan of attack seems like a nice blend of putting some of the things back the way they were originally with some of the newer products now available on the market. We would also still ultimately end up with a conditioned attic space for our seasonal things.

    Does this answer everyone's questions about what we think we'd like to do to fix our mistakes of long ago? And, is it logical?


  43. #43
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    Default Re: From gable vents to Ridge & Gable Vents

    I donít think there is actual term for the area behind a knee wall. I refer to areas like this as dead air space, as it has no real use and no air movement. In homes Iíve seen they usually have an entrance panel so you can crawl in for access to electrical boxes, or whatever???

    Jerry did a good of explaining the drafty homes of the past. Homes are tighter today and proper ventilation is more of an issue, way back when this was not an issue. I canít tell you how many old homes, that Iíve seen, that did not have insulation in the walls or attic, thus there was no need for any venting as the whole house could breath. Not sure about your home or area, but they may have used gable vents and that was it, my guess being they figured they would have air movement, or enough to not worry about it. My parentís old home only had gable vents and it never had a problem in the attic.

    In some of the old farm homes around here they had nothing, no vents or insulation, in the winter all the snow melted off the roof, didnít have to worry about ice dams, unless it was super cold, then throw more wood/coal in the burner. In the summer you didnít have A/C so need to worry about cooling costs, and you left everything open to try to keep the home as cool as possible. You didnít see any issues with the structure or problems in the attic.

    I think you have a good plan, but I think I would wait until you can do it all at once, might cause more problems it you do one long step at a time. I would pull back some of your insulation and check for any issues and if all is good leave it as is. In the spring, fall, at a time of high humidity (summer), and middle of winter check for issues in random spots and if things look fine just wait.


  44. #44
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    Default Re: From gable vents to Ridge & Gable Vents

    The Secrete to good Attic Ventilation is balance, High and Low*. There are a lot of factors to consider but a big mistake I see with especially with the newer homes in my area are no soffit vents or a lack of ventilation at the lower end. If you have more vents (or heaven forbid an attic Fan) you will be stealing conditioned air out of the house as the make-up air for the high vents. Very few homes have the air sealing to an extent to stop or even minimize this "Stack effect". the best air sealing, is a good layer of Cellulose insulation in the attic. (Not Fiberglass)

    I'll lay money down that only 1 in 20 homes in my area even come close to the 1 sf./300 sf. of attic space, vent recommendation. In my area we don't normally have to worry about moisture, but hot attics.

    *In my opinion it is better to have slightly more vents at the low end than overdoing it at the top. This minimizes the chance of the stack effect and pulling conditioned air from the home.


  45. #45
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    Default Re: From gable vents to Ridge & Gable Vents

    We're thinking you might have a point about scoping out the situation first. We're thinking with a flash light and mirror we can gently remove some insulation and then look up and down the empty space between the insulation and roof decking, much the same way we check the chimney from the clean out below. And, if it's not bad, leave well enough alone until it's time for the roof to be done and then take care of venting it properly then. We are now leaning toward doing this as it makes the most sense.

    On a side note, as a kid, the space behind the knee wall was the best hiding place ever. I had a couple of weddings to attend this past weekend and started reminiscing with my siblings. They reminded me of how we used to crawl to either end of the space, peek down to the outside through small louvered vents, and make odd noises out them much to the confusion of our puzzled neighbor. It was great fun. Also, none of us remember any insulation. In the summer we always had all the windows open; we had no AC. Nobody had AC. If it got too hot, we'd create "tents" and slept outside.

    So in hindsight, there were high gable vents for the space above our attic bedroom ceilings, we remember those, and there were those low gable vents in the crawl spaces we peeked out. So I guess this is how my dad vented. There would have been air in from those low vents, up the empty slanted attic ceiling rafter space, and air out the top gable vents. And, your right, I don't remember there every being any sort of rot or funny smells up there because it all could breathe.

    Have you come across old houses with low gable vents for the knee wall crawl space with high gable vents at the top? Or, was this something unique to my dad, he was a bit of a "Rube Goldberg". Maybe this was unusual as we don't remember any of our friend's houses having these peek outs.


  46. #46
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    Default Re: From gable vents to Ridge & Gable Vents

    Quote Originally Posted by Scott Patterson View Post
    If the home does not have soffit vents and you block the gable vents then the ridge vent will not do anything. You must have two sources of air.

    You are correct that the gable vents should be covered, but that is only if a lower air supply source is added. Like soffit vents, but if the design of the home does not allow for this the gable vents and ridge vent combo are better than nothing.
    This is interesting and helpful. I have been helping my Mother-In-Law renovate a house she bought...built in the late 1930s. There is no "easy" way to install soffit vents....the attic is closed off down to the soffits, and the eaves have "non-perforated" aluminum. To do it right, I'd need to drill holes in the eaves, add perforated soffits, and somehow drill/cut a path for that air into the attic...not a job I'm willing to take on.

    In her case, there were two gable vents...so we just added a ridge vent as the next easiest method to get "some" airflow...even if not ideal. I'm wondering, though...could I block off the current gable vents, which are located up high on the gable...and instead install similar gable vents closer to the floor of the attic? This would be relatively easy to do....just wondering if it would help with airflow.


  47. #47
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    Default Re: From gable vents to Ridge & Gable Vents

    I havenít seen homes with the low vents behind the knee walls, but it makes sense, maybe your dad was on to somethingÖ

    Adding lower gable vents might help as some lower air flow is better than none. Iíve seen a few homes that have the gable vents still in place after a ridge vent was installed, and I donít know of any issues. I don't see any harm in adding some type of lower level venting.


  48. #48
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    Default Re: From gable vents to Ridge & Gable Vents

    My dad was a bit of an out of the box thinker. He installed seat belts in our old 1957 Chrysler Station Wagon with rear facing third bench seat well before they became standard in cars. He took nine sets of airplane seat belts and bolted them to the car floor and feed them up between the seat backs and bench seat cushions. Most people didn't know what they were because most had never seen anything thing like them.

    My dad was in the Army Air Corps (previously known as the Air Service and the ancestor of what is currently the Air Force, for those unfamiliar) and that is where he was exposed to seat belts. Our seat belts didn't match the car's interior, as they were green, but who cared; we were safe and we thought they were cool. So like you say, maybe he was on to something. I'm glad to hear that what my dad did to vent the crawl space behind the knee walls was not far fetched and without merit.

    This gives me some food for thought and perhaps an option for us that could extend the life of our current problem-free roof, should we find the roofing deck is okay. We've always liked the idea of 'finishing' off the attic space, as in giving it some sort of knee wall and collar beam ceiling. We could protect the foil side of the insulation with a combo of sheet rock and/or acoustical ceiling panels. Our current insulation has been punctured and duct taped in several places, due to our moving some things around over the years.

    Perhaps we could put in true knee walls, as in the height of one's knees, and create an unconditioned tunnel behind them and vent this space with low gable vents in the low triangular gable walls of these spaces. We could also creating a collar beam ceiling with unconditioned tunnel above it being vented by high gable vents in the upper triangular gable walls. The combination of these lower and upper vented spaces, could end up giving our rafters the extra air circulation it needs. So in theory, it could extend the life of the roof, provided of course we find it not be be damaged.

    In addition, by putting in the really short knee walls, they would be set far enough back such that any first floor lighting fixture wiring would still be within the conditioned space of the attic and not a leak problem. The only break in the insulation would end up being our plumbing vent where it makes its way up and out the roof. Here we would be sure to maintain a good seal.

    Well, we have lots to mull over. Of course if I've just made some sort of blunder in my thought process, please feel free to tell me I'm not operating with a full deck. Otherwise, thanks for everyone's help and input.

    Enjoy the long weekend and the last hurrah of summer!


  49. #49
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    Default Re: From gable vents to Ridge & Gable Vents

    WowÖ rear facing car seatsÖ forgot all about those things, now I remember the people looking back at you driving down the roadÖ

    I think you found a solution that will work for you with the knee walls and ceiling, and guessing you will find things in good shape.

    Last hurrah of summerÖ going to be 98+ today and 90ís into the weekend, us up North can do without it, we were hoping summer was over after our record heat wavesÖ


  50. #50
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    Default Re: From gable vents to Ridge & Gable Vents

    If the knee walls go to the underside of the rafters, and if the rafter bays are filled with insulation, there will not be any benefit for trying to ventilate the knee wall space as there will not be any significant area to even ventilate.

    Jerry Peck, Construction / Litigation Consultant
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  51. #51
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    Default Re: From gable vents to Ridge & Gable Vents

    We thought those rear facing seats were the best as kids and of course, we had to take turns. It was a big deal to get back there because we enjoyed either waving at people or making funny faces at them. Heck, sometimes we held up signs we'd made. May fond memories.

    Meanwhile, in reply to Jerry, if we decided to go this route because we found the roof deck to be okay, I figured we would insulate the slated part of the attic ceiling in the same way we had years ago by leaving a space between the insulation and the decking. Of course, this would be made easier now a days, as there are those rafter baffles now available. So if we did this...

    The idea is to insulation floor of the small triangular space behind the short knee walls, then up the backside of these knee walls, then continue up the slope of the rafters (as mentioned above), then across the upper side of the collar ties, and then back down the other side in the same manner.

    Since my house doesn't have soffits nor would I have any sort of drip edge roof venting system at this point in life, I wasn't thinking of packing this small space behind the short knee walls with insulation. Just line it as mentioned above.

    This is why I was thinking of using simple gable vents to vent the small triangular space behind the short knee walls (like my dad did many years ago) in combination with the rafter baffles and upper vents above the collar beam ceiling.

    I was hoping this would give low 'air-in' venting which would travel up the rafter baffle of the slanted section of ceiling into to the 'air-out' venting of the top tunnel space.

    In the beginning, the high venting would be our existing ridge vent. Then, hopefully, years down the line, when the roof does become too old, we could make up our mind about whether to leave the ridge vent or close it up and use high gable vent instead.

    Does this make sense? Or did I misunderstand you?


  52. #52
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    Default Re: From gable vents to Ridge & Gable Vents

    Attached is a drawing of what I think you want to do, and from what you remember as a kid. I threw in the "SmartVent" as an option, but with just gable vents I would skip it. I didn't draw it, but the existing ridge vent would be fine with the low gable vents.

    You will also want to keep the insulation from falling out of the knee walls, such as stapling strings along the open backside of the studs, I never trusted the paper faced stuff as I've seen the insulation fall away from the paper in attic spaces, for example around skylights.


    Attached Files Attached Files
    Last edited by Mike Kleisch; 08-30-2012 at 11:12 AM.

  53. #53
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    Default Re: From gable vents to Ridge & Gable Vents

    Yes, that is exactly what I'm thinking we could do, if we find the roof decking is fine. The only difference would be to depict the ridge vent as an initial option to the plan. As we could continue to use the existing ridge vent until the roof become too old.

    At that time, we could decide to either leave the ridge vent or close it and use the high gable vents as you show in your drawing. We could also decide, at that time, to have smart vents put in along the drip edge of the roof.

    The knee walls would be very short. This would keep the top side wiring of the central ceiling fixture of each of the first floor rooms within the conditioned attic space.

    Thanks for adding a visual aid to illustrate what I was thinking off.


  54. #54
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    Default Re: From gable vents to Ridge & Gable Vents

    Quote Originally Posted by Mike Kleisch View Post
    Attached is a drawing of what I think you want to do, and from what you remember as a kid.
    That would work if the rafters were of sufficient depth to allow for the full insulation depth plus the air vent depth as shown - compression insulation reduces its effectiveness, so that must be considered before doing as illustrated.

    Jerry Peck, Construction / Litigation Consultant
    Construction Litigation Consultants, LLC ( www.ConstructionLitigationConsultants.com )
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  55. #55
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    Default Re: From gable vents to Ridge & Gable Vents

    We have 2x8 rafters. So I think they are probably deep enough to accommodate both the rafter baffle and insulation without compressing or squishing the batts. Correct?


  56. #56
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    Default Re: From gable vents to Ridge & Gable Vents

    Quote Originally Posted by zippet View Post
    We have 2x8 rafters. So I think they are probably deep enough to accommodate both the rafter baffle and insulation without compressing or squishing the batts. Correct?
    2x8s are 7-1/4"

    R-30 batts are typically 9-1/2" give or take (depending on manufacturer)

    7-1/4" less 1-1/2" for ventilation = 5-7/8"

    9-1/2" R-30 compressed to 5-7/8" = approximately a 40% compression

    9-1/2" thick R-30 installed in a 5-1/2" cavity reduces the R-value to R-21, so your 5-7/8" cavity may give an R-22, maybe.

    So, no, if you are going to do what I think you are, you will not get your R-30 you probably need.

    Jerry Peck, Construction / Litigation Consultant
    Construction Litigation Consultants, LLC ( www.ConstructionLitigationConsultants.com )
    www.AskCodeMan.com

  57. #57
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    Default Re: From gable vents to Ridge & Gable Vents

    This has become a conversation with zippet. I have thoughts to express. First, I want to know about those 2x8 rafters. I see 2x8 floor joists above a bungalow first floor. 2x6 floor joists for most attics. 2x4 roof joists/ rafters. 2x6 roof joists rarely. Do you really have 2x8 supporting roof sheathing? At what spacing?


  58. #58
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    Default Re: From gable vents to Ridge & Gable Vents

    Sorry, for the delay. We were enjoying the weekend with my brother and his family in PA. You made me doubt my memory, so when we got home, I pushed a small edge of the insulation aside and slid a very flat ruler in until it came in contact with the underside of the roof decking. Sure enough, it was 7-1/4"; the rafters are definitely 2x8's and they are 16" on center. If you are interested, the floor joist are 2x6's and 16" on center. The collar ties are 2x4's, 32" on center.

    In addition, the roof decking and attic floor is tongue and groove planks. The house is also sheath in these planks which run on a diagonal from the side mid-line of the house - downward and outward. The ridge runs side to side, the full width of 25', with the rafters running perpendicular to the ridge in which they meet in the middle over the supporting wall. The house is 30' front to back; so we have a footprint of 25'x30'. The bottom of the ridge is 7-1/2' to the top of the tongue and groove attic floor planks and we have an approximate roof pitch of 7:12.

    The attic stairs is centrally located, running parallel with the pitch of the roof, back to front. The stairwell comes up into the attic between two joist in which the middle one has been partly removed and boxed out reinforced sistering and headers at both ends of the opening. I guess they don't make things the way they used to 72 years ago. Phil, I hope this helps with what you were wondering about.

    Meanwhile, in response to Jerry pointing out that R-30 rolled batts are 9-1/2" thick, makes us realize we are going to have to think a bit more on how we plan to replace the 28 year old stuff that's up there now. This new realization has us puzzled in particular because of Phil questioned whether or not we really did have 2x8 rafters. So, if most people have smaller rafters, what the heck do they do, if they want to use their attic for a conditioned storage space?


  59. #59
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    Default Re: From gable vents to Ridge & Gable Vents

    Hey, just wondering, given the issue with R-30 insulation batts not fitting in 2x8s rafters properly, we are starting to think perhaps, when the time comes, it might just be easier to revert back to unconditioned attic storage as was the case when we first moved in 31 years ago. If we re-install the insulation to between the floor/ceiling joist, what is the required R-value needed in this case?


  60. #60
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    Default Re: From gable vents to Ridge & Gable Vents

    Hello Zippet,

    I think a roof is going to last longer where it is floating in the outdoor environment, not an energy and moisture engine of the house shell.

    I accept most of what Joe Lstiburek says here:

    My alternative view of attic venting is that a solar powered roof fan makes sense if in Summer, there are very large gable openings, as in an opened window. This can cost less, and will avoid regrettable slotting and weakening of roof sheathing. Keep the roof simple.

    I build thick attic floors, almost fully decked, with as much insulation as space allows, minimum R38.


  61. #61
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    Default Re: From gable vents to Ridge & Gable Vents

    The more we are thinking about it, the more we are thinking it might be best to just revert the attic back and not use it for storage. We should probably get rid of most of our junk anyway. What's the expression - Keep It Simple Stupid!

    Speaking of which, and this might be really dumb to ask, but is it possible to achieve the required R-Value by combining the resulting R-Effects of insulating the 2x8 attic rafters and 2x6 joist?

    I know there would be a big dead air pocket between the two sets of insulation, but it would allow us to work with the lumber sizes we have and end up with a combined R-Value of 30+ above our living space. Does this work?


  62. #62
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    Default Re: From gable vents to Ridge & Gable Vents

    Insulation in roof joists is wasted and a nuisance, in a vented attic.

    Here is an example of attic floor insulation with ample decking.

    Last edited by Phillip Norman; 09-07-2012 at 10:34 AM.

  63. #63
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    Default Re: From gable vents to Ridge & Gable Vents

    Interesting and clever idea. So, basically you filled the existing floor joist and then built an egg crate atop of these joist to accommodate the additional height needed to fill with the remaining insulation required to meet the R-Value. Couldn't this additional lumber put too much extra weight on the joist and cause possible stress fractures to our plaster ceilings below?


  64. #64
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    Default Re: From gable vents to Ridge & Gable Vents

    We have moved beyond the thread topic. I will carry this further, with anyone who contacts me. It may not be a topic for this forum. The result is: a tight thermal and air barrier over the home heated spaces. Much more sure of achievement than some contraption above the attic floor. I am dealing with a simple attic, but the thread has been open to bungalow or whatever, other construction is called. I rarely know what to do with such other construction. For example, I opened up soffits to breathing space over a cathedral ceiling. Now the insulation is wind-washed. Was the customer better off with inactive soffit vents? It's only a matter of slight impact on lifespan of associated shingles.

    My contact info.

    Last edited by Phillip Norman; 09-07-2012 at 12:27 PM.

  65. #65
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    Wink Re: From gable vents to Ridge & Gable Vents

    We have studied and researched the gable vent with ridge vent theory and believe that with the proper materials offered by DCI Products, this concept will be the acceptable norm soon.

    Using the patented DCI SmartRidge I ridge vent combined with existing gable vents covered with DCI Gable Vent Sno-Screen, will create the perfect air chamber for exhaust in all four seasons. You see, the fabric weather screen controls the flow of air in both directions and is controlled so not too much air can enter at any one time.The two rafter end bays will not have the slit cutout at the ridge (about 16" each gable end). This gable vent will act as the exhaust for that area of the roof. There will not be any short circuiting because the Sno-Screen and SR I are compatible with each other as the winds increase. The combined NFA is about 18 NFA including the gable vents and the SR I. Mathematically it works and in the field it works.

    The SR I will be installed completely across the roof, gable end to gable end. The no-lift side will be installed on the front of the house so no lift up is visible. If soffit vents are not present or not adequate, use of the DCI SmartVent will be required as intake. The NFA for the ridge vent is about 12 NFA (but is 100% efficient) and the gable vents add up to the remaining amount of NFA required for the exhaust (usually about 18 NFA). The gable vents can be sized correctly but need the protective fabric which allows air flow but curtails high winds, rain, sleet or snow from entering the attic. This system will allow for the required air exhaust in heavy snow areas in the winter because much less air flow is required in the winter due to the cold, low pressure air. Summer is warm and high pressure which requires much more movement of air. Without keeping the gable vent open during the winter, the snow will choke off the air flow out the ridge vent at least until the peak snow melts. Why even take that chance when a system eliminates any choking of the exhaust venting.

    Solar roof fans can be used successfully with our passive SR I attic ventilation system to extract additional warm air if a homeowner requests it. The placement of the fan is critical. It must be equal vertical distance from the soffit and the ridge and equally spaced horizontally with the gable ends of the roof. This will draw additional air out from the center of the attic when running and will act as intake/exhaust when it is off since it is equal distance from soffit to ridge.

    In another thread I can discuss our concepts on one sided and two sided ridge vents as well as the SmartBaffle insulation blocker that can be installed to protect the soffit insulation from cutting off the air flow.

    Check out Leading Manufacturers of Attic Ventilation Building Products and Gutter Protection to see the SmartRidge I ridge vent solution.

    Please let me know your feed back and questions.


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