From gable vents to Ridge & Gable Vents

[Mike Kleisch]

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?

I think you are starting to suffer from information overload. First, decide what you want to do with the space. Then, decide which method of insulation you want to use. And finally, decide on how you are going to vent it. Personally, I think the gable end vents like the way it used to be is fine, and in your case probably the best option. I would consider adding the lower end gable vents that were discussed before, if you use the attic space with the knee walls.

If you want to use it as conditioned storage space you will have to insulate the rafters. I’m not sure how much space you want, but you can always insulate between the rafters, leaving a 1-1/2 inch air gap and then install foam board to get your required insulation value, and yes, you would have to rock over the foam.

If the attic will be attic space, no storage or conditioned space, then you need to remove all the insulation from the rafters and insulate the attic floor, since you would not be putting anything in the attic you could just blow the attic floor with insulation until the needed R value is reached.

I would not insulate the rafter area and the ceiling area like you asked, one or the other.

[Jerry Peck]

I would not insulate the rafter area and the ceiling area like you asked, one or the other.

But ... *IF* you do insulate the rafter areas, take into account all that has been mentioned, including the depth of the rafters, the thickness of the insulation, and that any knee walls and gable ends will also need to be insulated and all that included area needs to be sealed from the outdoors ... otherwise there is no need to even insulate between the rafters.

[zippet]

Yeah, you're right, there is a lot to digest, but it's all good and greatly appreciated. We now have a good understanding of the major dos and don'ts. Our gut tells us we'll probably find we got lucky. However, even if this is the case, we don't want to push the envelope going forward. Given this, our main goal is to get the roof vented correctly and not end up with our vents being too close. Whether or not we end up with storage, although nice, does not take priority.

We are relieved to learn, if we end up reverting back to the original gable vented unconditioned attic space, this will still work. We are also, equally, relieved to find, if we put in short knee walls, the low gable vents combined with upper vents will also give us the proper venting needed via a 1-1/2" minimum gap left in the rafters. Both methods will allow the roof to breathe and allow us to correct the problem of our plumbing vent being too close to the ridge vent.

So, after all is said, it the choice between these two venting options seems to boil down to which method of insulation would work best in our case. Filling the attic floor with the proper amount of insulation seems simple enough, but then we are left wonder how to seal off our full-size stairwell opening which has an attic door and enclosing walls at the top. Alternatively, we can leave the stairwell and most of the attic space within our conditioned air space by using knee walls and insulation to the outer side of any first floor intrusions, which would eliminate the need to seal these points.

So, taking all mentioned into account, the questions become:
-If we used loose fill, how deep do you need to go to obtain R-30+?
-If we didn't want to get involved with using a blower, can you roll insulation between the joist and then roll another perpendicular layer on top of the first layer to obtain R-30+?
-If we went with layering the rafter batts with foam board, given the batts are pressure fit against the sides of the rafters, do you need to seal the rigid board seams? If so, how is this done? And, why do you need to rock rigid foam board if the attic is just an attic and not habitable space?
-Given all of the above, which method is more likely for us to be able to accomplish on our own?
-And, is one method less fraught with possible error and mishap and less likely for us to screw up?

And, as a side note, I get why it would be better to use one or the other method above, but out of curiosity, is it technically possible to use a combined effort of the two methods to obtain a functional sum result of R-30+?

[Mike Kleisch]

Loose fill insulation R-value is determined by the manufacturer and can range from 2-4 per inch, with 3 being about average. Foam board insulation R-value hits around 4-6 per inch with 5 being average, but is determined by the manufacturer too. I really should say tested to determine the R-value.

Yup, you can use roll or batt insulation, try to keep joints snug and overlap each layer so joints are staggered.

If you insulate between the rafters with batt insulation and cover with foam, be sure to maintain the 1-1/2 inch air gap between the roof decking and batt insulation. You do not need to seal the foam board joints (case pending manufacturer), but I do recommend using all weather tape on the joints.

I mentioned the need to rock if you were to use the area as conditioned space, as exposed foam is not allowed inside the building envelope. If you were to close the attic off, you might be able to get away from the need to rock, but with the door and full staircase, not so sure, check with the AHJ.

I would go with insulating the rafters and gable end walls as this sounds like a handy storage area with the full staircase to it, or a possible room down the road. I can’t say what the best option is for you, as I have no idea of your comfort level or skill set.

Jerry mentioned R-30 for your area, in mine it’s R-38. One reason you can’t combine the two areas to create the R-30 is if you have a layer of R-19 batt insulation and install a layer of R-19 right on top of it you have close to R-38, but you loose some R-value due to joints and gaps in the insulation, not enough to worry about, unless it's real sloppy work. If you install these two layers apart, as in your case, you would have R-19 at the ceiling, and then a big cold air space with R-19 above it (rafters), you might only have, as a guess, an effective total R-value of 25, maybe more, or maybe no gain, all kinds of factors to consider.

[Phillip Norman]

I still think discussion of insulation tactics belongs in another thread, and invite zippet or anyone to contact me for direct advice. Insulation in rafters of a ventilated attic is not additive to floor insulation.

I believe in diligent attic floor sealing, gable vents, not caring much about inlet distribution around soffits, and wanting very large operable gable inlet, as in an open window, to serve any (solar) powered fan). If you want a cool attic in summer, rely on a powered fan. Don't wish for effectiveness in static vents.

Much of the hand-wringing is over guarding lifetime of composition shingles. I don't believe more can be achieved in ventilation, than can be achieved by choosing lighter colors.

Moss is the enemy in most places. Control that. Maybe install decorative copper ridges and cupolas.

Don't do crazy things hacking up a roof with lots of can vents or sheathing slots, not bothering to rebuild code-required sheathing strength. If a portion of a roof is soft underfoot, there likely will be caused leakage. Isn't slotted sheathing much more likely to zip off in a wind event?

Isn't this typical of what hack roofers or weatherization jerks do to cut in a can vent?

Don't codes say something about that? Here is a matter where home inspectors should care.

[zippet]

We were partial to fixing our venting problems with the short knee wall method, since it would eliminate issues relating to our staircase leading to the attic. However, the necessary foam board is very expensive and we are now wondering if the space is worth this extra expense. You see, our attic can never be anything other than non-habitable storage for multiple reasons.

Given this, we are starting to lean toward the other venting solution of reverting back to it's original unconditioned state by cross layering batts between and a top the floor joist which would allow the entire space to breathe. If we did this, it would mean we'd have to address how to handle our staircase.

Since the current ceiling of the staircase runs the ridge, this is obviously a venting and insulating issue and would need to be removed. Therefore, it would make sense to closed the staircase off at the bottom and create some sort of insulated hinged hatch at the top. Ironically, we were the ones that sacrificed two side by side closets to put the stairs in as a replacement to the pull down ladder that was there.

Funny enough, my grandparent's house had a 'secret' stairs to the attic. It was in the back of a clothes closet in which you pushed aside the hanging clothes in order to go up to the attic. We made up many stories about those stairs and it was always a question of who was going to be the bravest to venture through. It was our very own "Chronicles of Narnia."

Anyway, this is obviously going to take a lot thought and we will have to weigh out of all the related issues on how best to fix our venting problems as it relates to which method of insulation we should use. To think, I only discovered our problem when I happened to stumbled over the gable to ridge vent discussion and realized we'd screwed up all those years ago.

Ahhh...ignorance can be bliss! So, what's a few more grey hairs! Meanwhile, we would like to, once again, thank everyone for their input, suggestions, and pearls of wisdom. Thanks a bunch!

[J Cowles]

I have this type of soffit vent currently. These are original to the house including three gable vents.



They are highly insufficient for intake vents with the new ridge vent installed with my new roof. What I'm wondering...are there vent solutions out there for people who have small soffit vents? Are there concerns with opening up this type of covering? Will it just turn into a mess and have to be completely redone anyway or can I remove individual panels and cut holes through here to install more vents?

On the sides of the house there are windows. Is there a Window vent solution that would work? It would need to be something to keep rain and snow out in Minnesota. Or isn't that going to be low enough? I'm just not sure I can get enough ventilation with my skinny soffits without some sort of intricate and costly facia system. I got a quote on the Cobra FasciaFlow system, but it was $2,000. Still recovering from the cost of redoing the roof.



The attic is not finished and I don't plan to ever finish it, so everything is fairly accessible. The home was built in 1950. Any advice would be appreciative.

[Scott Patterson]

I have this type of soffit vent currently. These are original to the house including three gable vents.



They are highly insufficient for intake vents with the new ridge vent installed with my new roof. What I'm wondering...are there vent solutions out there for people who have small soffit vents? Are there concerns with opening up this type of covering? Will it just turn into a mess and have to be completely redone anyway or can I remove individual panels and cut holes through here to install more vents?

On the sides of the house there are windows. Is there a Window vent solution that would work? It would need to be something to keep rain and snow out in Minnesota. Or isn't that going to be low enough? I'm just not sure I can get enough ventilation with my skinny soffits without some sort of intricate and costly facia system. I got a quote on the Cobra FasciaFlow system, but it was $2,000. Still recovering from the cost of redoing the roof.



The attic is not finished and I don't plan to ever finish it, so everything is fairly accessible. The home was built in 1950. Any advice would be appreciative.

What is making you think that you do not have enough attic ventilation?

[J Cowles]

I was under the impression that the intake needed to be greater than the exhaust.

I am still in preliminary thinking on this. I need to ride out the winter and see if ice damns are still a problem. I also had issues with frost build up on all of the nails, but all of this was before the new ridge vent. So the intake > exhaust is my primary thoughts on why I should start planning for this.

[Jerry Peck]

The continuous soffit vents should have the net free vent area (in square inches per linear foot of soffit vent) marked on it somewhere.

If you cannot find the marking showing the net free vent area, and if this soffit material is still made by the manufacturer, then go to the manufacturer's web site and their web site should have that information listed. If that material is no longer made or if you cannot find any information on it, then measure the size of the holes, mark off one linear foot of the soffit, count the number of holes, multiply the number of holes by the area (in square inches) of the hole - that will give you the net free vent area per linear foot, then multiply that number by the total linear feet of soffit vent you have.

I suspect you may be surprised (good or bad ) of the total net free vent area you have.

Then calculate the net free vent area of the gable vent you have compare the two to see how their net free vent areas compare. Unless louvers are marked with the net free vent area, calculate metal louvers out at 70% of the vent area (30% of the vent area is blocked by the louvers) and calculate wood louvers out at 25% of the vent area (75% of the vent area is blocked by the louvers).

Typically, (there may be reason for having this, but I can't think of any) there is no reason to have gable vents and ridge vents, and especially there is no reason to have gable vents or ridge vents without soffit vents as the air needs to move from the lower soffit area to a higher area for proper attic ventilation.

[zippet]

Good news! Due to Hurricane Sandy we had to have our roof done sooner than we had planned; she ripped our 20 year old roof off. The tarpaper held up, so we had no damage inside. Anyway, we found out our roof deck was in excellent shape and discovered there was a 1/2 inch vent slot cut at the top of the fascia board above the gutters and below the bit of roofing shingles that overhand the roof line.

So as it turns out, all our rafters have been vented correctly all these years. We were so relieved. We also borrowed a wire USB camera from a friend, snaked it up into the space between the underside of the deck and topside of the insulation and found all was good, fluffy, and clean. Interestingly enough, the new ridge vent doesn't look anything like the old aluminum one. It looks like a roll of one inch thick black scruffy Brillo pad.

I have attached a photo I took with my cellphone of the 1/2 inch horizontal slot we found that had been cut all those years ago. The brown edge is the back wall of the gutter. I had to carefully lift the low edge of the shingles to hold the phone under them from within the gutter to snap, the picture, for all those who might be interested. Oh, yeah, we left the plumbing vent alone. The roofers would have gladly moved it, but we found out it was fine were it was. So we left well enough alone.

Thanks once again for everyone's pearls of wisdom.

[Phillip Norman]

Hello zippet,

I don't understand the vent provision in the fascia board from your one blurry photo. How is lumber protected against wetting and rot? Is there any screening, or absent that, have you found wasp nests and such? I like the idea of better invention in fascia boards. I still think slotting of roof sheathing invites trouble, whether for high or for low continuous vents.

[Charles Schiller]

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

Great article. Understanding attic ventilation is very important and in different areas of the country on why it is important for proper attic ventilation.

[zippet]

Sorry for the quality of the picture, but it was the best I could do with my freebie, non-smart cellphone. I don't know what to say, other then this horizontal slot was cut over 28 years ago and everything is rock solid and in excellent shape.

Also, I'm not sure if I used the correct term, by using the term fascia board as to what I believe is the 'end cap' to our rafters which are sticking out one, or at the most, two inches beyond the old diagonal tongue and grove planks that sheath our house, to which the original siding is attached and we insulated and vinyl sided on top of this old siding; the gutter ends up flat mounted through our sidings and I guess into this wood, as it is very solidly fastened.

The slot is not exposed. I had to gently lift the overhanging shingles and duck under look to take the picture of the 1/2 inch horizontal slot that was cut at the top of this board. Because the slot is under the overhang of the low edge roof line and shingles, the rain water or snow melt runs off this edge into the gutter missing the slot like an awning protects an open window.

Our house is the typical old style basic cape with no structural overhang or soffits. I originally posted because we feared our ridge vent was not installed correctly almost 29 years ago after we read something last year that made us start to think this. At that time, we were unaware of this low slot, and so thought we had no air drawing up the rafters.

When the roof was stripped clean, due to Sandy, before redone, we got to inspect the edge clearly with the roofers and that's when we discovered the low end air slot. Our roofers were old school, no pneumatic nailers, doing the roof using good old hammers. They were amazing and a pleasure to watch. In fact, we had old time neighbors come out to watch these true craftsman work.

Anyway, they said they have seen this before and the roof decks are usually in great shape, which ours was. The wood was all very solid throughout. I guess technically speaking if the gutter became completely filled and somehow the water level became higher than its outer edge and the water couldn't spill over this outer edge, there is a risk it could backup and get in.

However, in almost, now 29 years, through many hurricanes, nor'easters, and blizzards it has never happen. This includes the blizzard of last week that dumped three feet of snow. We have never shown any signs of water damage and the wood is clean, dry, and solid. We also didn't notice any wasp nest, perhaps we are lucky on that one.

We have actually discussed whether or not maybe, now that we know this slot exist, we should perhaps figure out a way to screen the slot. But then we wrap back around to the age old adage of "don't mess with success, if it ain't broke, don't fix." if it has work well all these years, maybe we should leave it alone.

Inside we have insulation snugged up between the joist (foil side down) squeezed in just under the insulation that runs from bottom to top between the rafters in which there is at least a two inch gap between the fluffy side of the insulation and the underside of the roof deck. I guess this piece of insulation at the bottom has acted much the way steal wool can be used to block holes from rodents. We have a trailer in the woods and we successfully do this around all plumbing cuts.

I hope this helps explain what it is we discovered we had that evidently has worked so well over the years. Let me know.

[Mike Kleisch]

I’m confused too, was this photo taken after the new roof was installed? If so, you have some issues to deal with. The brown discoloring you see is where, I think, the old drip edge extended down into the gutter, and would have covered the gap, but that is a guess. In your photo, there is no drip edge or any ice and water shield that I can see.

The exposed plywood troubles me. You should not be able to lift shingles up that easy to see exposed plywood. Drip edge should be installed first, followed by, at a minimum, roofing felt, or if required (also good practice) ice and water shield. Then, there should be a shingle starter roll along the bottom edge followed by the first course of shingles. If this was all done there is no way you are lifting up a piece of shingle and seeing plywood.

If that gap edge is exposed w/o screening insects will move in and possibly bats.

This diagram pretty much sums it up:

[Scott Patterson]

What that gap/cut is for is called "drip edge venting". It is not very common and requires a specialized piece that acts as flashing and also venting screen for the soffit under the area.

This is a link to various types of roof venting you might see....
Roof vents | NRCA National Roofing Contractors Association

[ted kidd]

I accept most of what Joe Lstiburek says here:

Yep, go to buildingscience.com or healthyheating.com for buildingscience related questions.

Jerry Peck seems to have some building science experience, litigation consulting, that should give others pause.

To the OP John Mackay; when changing the pressure envelope of a home it's a good idea to perform "worst case" combustion appliance testing before and after to determine if you've caused a change to the pressures experienced in the combustion appliance zone, particularly if appliances are natural draft.

I know of one case where a ridge vent was added and burning a fire in the fireplace would cause backdrafting of the water heater. This condition was only apparent because the two chimneys were adjacent, so the basement would fill with wood smoke.

If not for the wood smoke this dangerous condition would have gone unnoticed, possibly making people sick or worse...

[zippet]

The photo was taken after the new roof. This, good or bad, is what I know/see:
- I did not see, what is being called a metal drip edge in the picture provided above, along the edge of the old roof nor this new roof.
- There was an ice shield rolled out and installed along all edges of house and garage before the roofing felt and then architectural shingles.
- The gritty dark stuff, seen in the photo, is the edge of the ice shield adhered to the top of the roof deck, and I can only see this by peeking under the overhanging edge of shingles; I didn't lift the shingle by much, just enough so I could see under the overhanging shingle edge when I tilted my head while holding the cellphone under such and in the gutter, otherwise the slot is not visible; we clean out our gutters a few times a year and have never noticed the slot in over 28 years. Granted we are up on a ladder looking down on the gutter and we never thought of looking under, up, and back.
- The overhang of shingles beyond the edge of the roof deck is about two inches, which was the case with the old roof.
- The wood seen in the photo is the edge of our tongue and groove roof deck planks, not the cut edge of the slot; the photo is not very good.
- Our house was built pre-plywood, so there is no plywood; it is entirely sheathed in cedar tongue and groove, then our original siding, then exterior rigid insulation, then the final layer of vinyl siding.
- The cut for the slot is not visible in the photo as it is just behind the brown aluminum trim seen in the photo; the back wall of the gutter is up against this brown aluminum trim with the top back edge of the gutter about one inch down from the top edge of this brown aluminum trim.
- The top edge of the brown aluminum trim is approximately the bottom edge of the cut slot.
- The gutter attachments go through all and bites into the underlying wood.
- When we used the wired USB camera we borrowed, to inspect each of the rafter spaces, we also used it to peek in through the slot and we could make out the back edge of that insulation piece we use as a 'plug' at the bottom; all looked clean in there too.

I'm also thinking now, that I agree about perhaps it being a good idea to figure out how to screen up the vent slot. Maybe we could slide the bottom edge of a screen strip behind that brown aluminum trim and staple the top edge to that edge of tongue and groove roof deck.

Anyway, I hope this further helps detail what it is we have.