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  1. #1
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    Default Frost in the Attic

    Forgive me, but we here in Seattle don't see many freezing temperatures (until this week) and I haven't seen frost buildup in the attic space. How concerned should I be about this?? The situation is a 2000 build, the North side of the sheathing (from the attic) had a layer of frost. I had adequate ventilation and adequate insulation (aside from a few areas where there were footprints). Is this "normal" for freezing temps or should I never, under any circumstances have frost buildup on the sheathing?? Thanks in advance!

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    Default Re: Frost in the Attic

    Looks to me that you have a moisture problem in the attic. Do bathroom or kitchen exhaust fans discharge into the attic?

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    John Kogel's Avatar
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    Default Re: Frost in the Attic

    Any ice is too much. There should never be that much moisture in the attic.

    Most likely, warm air is leaking up from the living space somehow. I would call for a repair, further investigation, etc.


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    Default Re: Frost in the Attic

    Pretty common to see in older houses here in MN. Additional insulation and possibly ventilation is needed in the attic.

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    Default Re: Frost in the Attic

    I have to agree that any ice is too much, BUT, you are in a very wet area, no?
    Think about your weather before the temperature dropped and how rapidly it dropped.
    If you had a 80+% humidity at say 50 degrees and the temperature drops quickly to below freezing, then the moisture is already in the attic and will plate out on the cold surfaces.
    It bears looking into, but if you did not see any evidence of moisture damage on a 9 year old house, combined with funky weather, maybe it is just an anomaly.

    Jim Luttrall
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  6. #6
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    Default Re: Frost in the Attic

    Frost in attic is caused from warm Moist air getting into attic .It is caused by stack effect.
    Look for Exhaust from bath or Kitchen vents into attic,
    they must go to the outside ( not to Roof vents or to soffit.
    You can also look to Attic door not gasketed and insulated it might need more weight to help seal the gasketed door..
    pot lights not sealed they should have a dry wall box enclosing them .
    All electric boxes in ceiling can be leaking into attic .
    There could considerable heat being lost via these vent holes .
    Insulation added still will not stop this warm moist air getting in to attic .
    Another cause could be over venting the attic with electric or air operated roof vents puling more aid from the home.
    You could have negative pressure in attic with no soffit vents .
    Roy Cooke


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    Default Re: Frost in the Attic

    I do not work as a Home Inspector, but have been reading this Forum for several weeks, and think I "belong." I think I have methods to share, in ability to produce informative reports.

    Please consult the attached pdf document, to understand a report of mold in roof sheathing of a home in Portland Oregon. At issue is whether mold would be controlled by vacuuming cellulose from accessible reaches into sloped ceilings below the upper attic.

    I seek a consensus test of my assertion that mold in a roof is always due to a roof problem. Further, I assert such problems are subtle, with periodic wetting and not with flow that would produce complaint and repair. An example, and a common issue, is improper placement of felt paper under asphalt shingles. Felt paper error might run the full length of a roof.

    Portland is really cold right now, and I imagine photos in this attic would be interesting. I imagine I will be up there again, soon.


    At March, 2010, I redirect the reader to consensus advice in this thread. Get rid of the moisture source! My customer fixed his problem, with major re-roof over a troublesome bathroom. The re-roof allowed installation of a proper through-roof bath fan. My insulation of the attic did not need any correction. A lot of insulation did aggravate the mold problem, with roof sheathing running colder. The attached file has been replaced, where viewed through the link in my second post to this thread, at an editable collection of documents on my Google Sites web page. I assert that a Google Sites web page, accepting pdf attachment, is a way for home inspectors to set up a personal report vault for each customer, viewable without download, and amenable to corrections. I face storage limit problems with my posts. I think the limit is 200 MB. I will look to free up space by not directly uploading pictures, rather referencing them at Picasa Web Albums.

    Attached Files Attached Files
    Last edited by Phillip Norman; 03-20-2010 at 07:00 AM. Reason: My naive advice might mislead the reader.

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    Default Re: Frost in the Attic

    Research Report Download

    Unvented Roof Summary Article

    by Kohta Ueno — last modified 2009/07/10


    This article was written to tie together and summarize the various papers on unvented conditioned cathedralized attics found on our website. We realize that there is a wealth of information, and much of it too detailed to understand or digest in a single sitting. Furthermore, building officials might not have the time available to carefully examine the many documents on the page; this is meant to summarize the main arguments, and provide pointers to where detailed information and measured data can be found.
    Click here to get the file
    Size 1.4 MB - File type application/pdf

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  9. #9
    Ken Rowe's Avatar
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    Default Re: Frost in the Attic

    Quote Originally Posted by Phillip Norman View Post
    I do not work as a Home Inspector, but have been reading this Forum for several weeks, and think I "belong." I think I have methods to share, in ability to produce informative reports.

    Please consult the attached pdf document, to understand a report of mold in roof sheathing of a home in Portland Oregon. At issue is whether mold would be controlled by vacuuming cellulose from accessible reaches into sloped ceilings below the upper attic.

    I seek a consensus test of my assertion that mold in a roof is always due to a roof problem. Further, I assert such problems are subtle, with periodic wetting and not with flow that would produce complaint and repair. An example, and a common issue, is improper placement of felt paper under asphalt shingles. Felt paper error might run the full length of a roof.

    Portland is really cold right now, and I imagine photos in this attic would be interesting. I imagine I will be up there again, soon.

    I don't believe your mold in the attic was caused by frost. Generally mold in the attic is caused by high humidity levels in the home. A furnace humidifier set too high for long periods of time, moisture intrusion in the basement or even excessive amounts of plants in the home. As someone stated earlier, stack effect. Humidity in the home rises to the attic and gets trapped. Another contributing factor would be the lack of proper ventilation of the attic space. Generally you'd like low and high ventilation, roof or ridge and soffit vents.

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  10. #10
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    Default Re: Frost in the Attic

    In my 34 years as an inspector in a cold climate, Twin Cities, Minnesota, I believe that nearly all frosted attics have their source of moisture from inside the house:

    1. Air leaks from the house to the attic at various penetrations: aka attic bypasses. The amount of frost depends on the indoor relative humidity, the total cross sectional area of the bypasses, and on the pressure differential between the house and the attic (stack effect). These are most common here in homes built before 1985. Since then most penetrations get sealed with sheet metal or foam caulk. Homes with damp basements often have frosted - moldy attics if bypasses are present.

    2. Unvented or poorly vented range hoods and bathroom fans. (Recently shown as a concern on an episode of "Ask this Old House".)

    3. Loose or deteriorated vents from combustion appliances. (This is the worst and will ruin the roof sheathing in one season if not corrected.) This condition will produce so much moisture that ceiling leaks will develop during periods of extreme cold when the heating plant is frequently operating and while attic temps are very cold.

    Attic ventilation RARELY solves these problems. The solution is to control indoor humidity AND eliminate the pathways for moisture to reach the attic. (seal bypasses, fix vents, etc.) Increasing attic ventilation alone simply increases the flow of moisture INTO the attic and further lowers attic temps, which actually worsens the problem.

    Last edited by Roger Hankey; 12-11-2009 at 06:39 AM.

  11. #11
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    Default Re: Frost in the Attic

    Somethings wrong. Any frost is too much. It has been 5 to 10 below here for the last week and I don't see frost in the attic. Plus it can cause mold over time. During the nigh frost forms, then when the sun hits the roof it melts and absorbs into the OSB. This cylce continues for a while, then in the spring when it warm up and the OSB is saturated. Poof, mold and mildew.


  12. #12
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    Default Re: Frost in the Attic

    Not sure of the construction style (slab, basement or crawlspace) but it is not uncommon to see frost, sometimes much more severe than your example, caused from a wet crawlspace. Physics. Water vapor rising from a damp/wet crawlspace will plate out on the cold underside of the roof deck and freeze. We have the related issue with mold growth in the attic then with the repeated wetting and drying of the roof deck.

    Bill


  13. #13
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    Default Re: Frost in the Attic

    That much water on roof sheathing is a problem, even though it is frozen water. I would report it and recommend further evaluation. What we don't know is why it is there. What we do know is that it should not be. There is a possibility that it is an anomally which may not reoccurr but as it was observed so should it be reported. There are times when we may be unable to ascertain the cause of a defect due to the time restrictions of the inspection period. Further evaluation is waranted here as this condition may have both structural and health related consequences.


  14. #14
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    Default Re: Frost in the Attic

    Reis,

    I am an inspector who operates north of Seattle. The moisture has always been present you just didn't see it. I noticed in the first picture that the a vent fan hose is disconnected and probably laying in the insulation. As other have said you need to look for the source of moisture that is coming from the living space. The mold/mildew will always show up on the north side of the roof and in advanced cases migrate to other exposures.

    Pictured is a home I inspected yesterday. Picture on left is next to gable end. I thought the roof had fire damage at first glance but mold/mildew hadn't turned into rot/fungus yet. Source of moisture was attic hatch that only partially cover hatch opening.

    Your attic looks pretty well ventilated but you may want to consider a fan hooked to a humidstat.

    //Rick

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    Last edited by Rick Bunzel; 12-11-2009 at 03:39 PM. Reason: add pics
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  15. #15
    Jerry Peck's Avatar
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    Default Re: Frost in the Attic

    Quote Originally Posted by Reis Pearson View Post
    I had adequate ventilation and adequate insulation ...
    Reis,

    Whenever you see things like in your photo, I would hesitate before stating there was "adequate" ventilation as better ventilation may well hep prevent that, which would mean that what is there is no "adequate".

    Now, if by "adequate" you mean 'the code required' amount of ventilation, then I would stay away from the term "adequate" anyway.

    Like others (or so it seems as I read the above), I suspect two things:
    - too much air exfiltration from the living space into the attic
    - the humidity may have already been in the attic and a sudden and dramatic temperature drop simply freezes the moisture in place
    - which gets back to 'too much air exfiltration from the living space into the attic'

    Which indicate inadequate ventilation (allowing air exfiltration from the living space into the attic means that more ventilation is needed to off set it. Which is not so much of a ventilation problem as much as an air exfiltration problem.

    Jerry Peck, Construction / Litigation Consultant
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    Default Re: Frost in the Attic

    ("Your attic looks pretty well ventilated but you may want to consider a fan hooked to a humidstat. //Rick ")

    I think I would be carefull in adding a fan exhaust as this could lower the pressure in the attic and cause more of a problem by drawing More warm moist air from the home .

    I expect not to far in the future we could stop venting attics ,it is done with some homes now and they did not vent homes many years ago.

    Roy Cooke


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    Default Re: Frost in the Attic

    I have moved in on this thread, with alternative discussion of a home with attic mold. I hope this is beneficial, that frost/ humidity/ mold are all the same for cause and action.

    My first, and only previous post, offered a pdf report that includes report-making methods that I am proud of. I hope the report-making will warrant a separate, new thread. I offer not only good pdf reports, but a better way to display and discuss them. Here is a link to an update of my report, and the action I recommend based on the good judgements I have observed in this thread. All inspectors might choose Google Sites web sites where their customers could view personalized reports via confidential links.

    Post to Inspection News, 12-11-2009 (Services by Phil Norman)

    I consciously do not post my conclusions here, wanting readers to follow my link. Please know, you will be able to view my new pdf without download. I hope with direct view, as with pictures in this forum, more people will bother to look.

    Phillip Norman
    Attic Access
    Portland, OR
    Home (Services by Phil Norman)

    Last edited by Phillip Norman; 12-12-2009 at 07:47 AM.

  18. #18
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    Default Re: Frost in the Attic

    Roger – as a newer inspector in Minnesota your insights are greatly appreciated. I have seen a lot of signs of moisture in attics especially in homes built in the ‘50s and ‘60s. One thing I’ve noticed in those homes is, if they have their original windows (double-hung, single pane with storms), the windows show signs of having moisture on them (or right now with how cold it is out you can see the moisture on the inside of them). Are these two issues usually related, or is it just that the windows are older and probably leaking like a sieve? Do you generally recommend that people monitor the humidity levels (turning down the humidifiers, etc.) in their homes when these issues are present? Does weather-stripping help those windows at all, or is replacement really the only way to stop the moisture build-up in the winter?

    Sorry for all the questions, but it's something i see a lot around here. Thanks.

    -Jon
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    Default Re: Frost in the Attic

    I would say that many homes are getting more air tight, this, with out removing the cause of humidity in the home can cause grief.
    I seldom see homes that now require a humidifier.
    I recommend get a recording device the shows what the humidity is in the home .
    I have a tight home and exhaust all Baths and kitchen fans to the outside on Timers .
    CMHC has Measuring Humidity in Your Home | CMHC some ideas to follow .
    My outside temp is 16° F inside 73°F and inside humidity is 40% no moisture on any windows .
    Long( to the floor ) curtains and drapes tend to have cold windows and moisture on them.
    I have a dehumidifier set at 50% setting drain hose to Laundry tub to help the high humidity if necessary.


    Roy


  20. #20
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    Default Re: Frost in the Attic

    You know that an attic is supposed to be a lot colder than the conditioned space?, and the house has to breathe without pulling too much of the air from the conditioned space into the attic and the vapor barrier is supposed to help prevent interior moisture, if any, from entering the attic. The outside of the walls from the foundition up are supposed to go up through the attic and out, this removes any moisture trapped in the walls. If you install too much insullation and cover the ends of the rafters and soffits then the attic will have a hard time venting what needs to be vented. I can not right now put a number of inches that start to no better but i am sure some one will post it, i hope. In the attic all ofthe white insulation it actually looks like too much, was there any vapor barrier at all installed in the attic? Maybe the frost is occuring fo a short time due to the roof not having the proper roofing material under the shingles and that is causing the roof to keep moisture to stay. Lots to look into.


  21. #21
    Jerry Peck's Avatar
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    Default Re: Frost in the Attic

    Quote Originally Posted by Cobra Cook View Post
    The outside of the walls from the foundition up are supposed to go up through the attic and out, this removes any moisture trapped in the walls.
    Not following what you are saying, but ... as I am understanding what you are saying (while acknowledging that I do not fully understand what you are saying) ... the exterior walls are required to be fireblocked and sealed at the floor and ceiling levels, which means there is no venting of the wall cavities.

    Please explain what you are saying better.

    Jerry Peck, Construction / Litigation Consultant
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  22. #22
    Roger Hankey's Avatar
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    Default Re: Frost in the Attic

    Quote Originally Posted by Jon Errickson View Post
    Roger – as a newer inspector in Minnesota your insights are greatly appreciated. I have seen a lot of signs of moisture in attics especially in homes built in the ‘50s and ‘60s. One thing I’ve noticed in those homes is, if they have their original windows (double-hung, single pane with storms), the windows show signs of having moisture on them (or right now with how cold it is out you can see the moisture on the inside of them). Are these two issues usually related, or is it just that the windows are older and probably leaking like a sieve?
    1.


    Do you generally recommend that people monitor the humidity levels (turning down the humidifiers, etc.) in their homes when these issues are present?
    2.

    Does weather-stripping help those windows at all, or is replacement really the only way to stop the moisture build-up in the winter?

    3. & 4.



    Sorry for all the questions, but it's something i see a lot around here.



    Thanks.

    1. Related? Yes. Indoor humidity is high and will condense on any surface colder than the dew point of the indoor air. Both the glass and the roof sheathing are below the dewpoint, or they would not be wet from the condensation.

    2. YES


    3. Weatherstripping is a good idea, but will rarely stop the condensation.

    4. Window replacement might be useful, but not necessarily cost effective.

    A low cost tool is a digital relative humidity gauge. This instrument reads the temperature of the air, its relative humidity and dewpoint. I find it useful to be able to show clients and homeowners the dewpoint of the air to help them understand why I recommend lowering the humidity in the house.


  23. #23
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    Default Re: Frost in the Attic

    Reis, Someone mentioned it earlier but I didn't see a response, can you tell us if the home is on a crawlspace or not? and if it is, is there a well sealed vapour barrier or is the dirt exposed ? I have often seen that to be the problem. Your attic may appear to be adequatly sealed and ventilated but it can simply be a matter of the ventilation being overwhelmed and not being able to "catch-up" due to the amount of humidity coming up from your crawlspace.

    Joe Klampfer RHI
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  24. #24
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    Default Re: Frost in the Attic

    Seattle huh? Geez you guys never have moister problems. But really, the frost you are seeing is most likely from a bathroom vent fan thats not exhausted correctly.


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    Default Re: Frost in the Attic

    moisture


  26. #26
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    Default Re: Frost in the Attic

    Jerry of course wall cavities are fire blocked at the top and bottom but i was referring to the outer wall between the siding or brick which have weep holes to provide an airflow to help reduce the humidity in the dead air space. this space is ususlly not air tight at the top or bottom and is vented through the soffits to the attic also


  27. #27
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    Default Re: Frost in the Attic

    What was the condition of the HVAC duct system.?


  28. #28
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    Default Re: Frost in the Attic

    Quote Originally Posted by Cobra Cook View Post
    Jerry of course wall cavities are fire blocked at the top and bottom but i was referring to the outer wall between the siding or brick which have weep holes to provide an airflow to help reduce the humidity in the dead air space. this space is ususlly not air tight at the top or bottom and is vented through the soffits to the attic also

    That air space is also supposed to be fireblocked at the top so it does not go up into the attic.

    Weep holes at the bottom - good, supposed to be there.

    Vent holes at the top - good, that helps create air flow for ventilation and drying out the air space ... good as long as the holes do not go up into the attic of soffit, that the holes vent to the exterior of the wall.

    Jerry Peck, Construction / Litigation Consultant
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  29. #29
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    Smile Re: Frost in the Attic

    The frost in the attic is a pre-curser to the developement of attic mold if left unchecked. This frost is indeed caused by moisture from within the home or building. It is however allowed to freeze on the attic sheathing due to a lack of ventilation in the attic space. Warm moisture laden air if not allowed to vent out of the attic will naturally cool within the attic. As the air cools condensation is the natural by product of the air cooling. I inspect homes in south eastern Idaho and see this condition all the time. I would suggest that in order to cure this condition that you advise additional ventilation be installed, and that indoor relative humidity be controlled by using exhuast fans when showering/ bathing, cooking, possibly installing a vapor barrier if needed in the crawl space. I have seen this condition develop when home owners used vaporizers extensively, or exhaust a clothe dryer into the home also. In my opinion the lack of ventilation is the biggest cuprit here, and ventilation definetly will not add to this problem. That opinion is definetly off base, not trying to be rude, but facts are facts.

    Ernie Tate
    TCS Home Inspections
    Idaho Falls, Idaho
    Builder for 35 years
    Full time home inspector for over 10 years


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    Default Re: Frost in the Attic

    And some Facts are not facts .
    Adding more ventilation could take more air out of the attic now with negative pressure in the attic we will get more air into the attic and much could come from the home .
    Stack effect is our problem
    This could only make the problem worse .
    Experience is a good teacher and reading will also help .
    I have both a good start is read this . Roy
    the house needs to be sealed better and close all holes to the attic.



    Measuring Humidity in Your Home | CMHC


  31. #31
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    Default Re: Frost in the Attic

    Quote Originally Posted by Roy Cooke sr View Post
    Adding more ventilation could take more air out of the attic now with negative pressure in the attic we will get more air into the attic and much could come from the home .
    I agree with this 100% (assuming we are talking about mechanical ventilation.)

    I have now read several post that mentioned the VB in the crawl space. Is it really possible for enough moister from the crawl space to cause condensation problems in the attic?


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    Default Re: Frost in the Attic

    I just helped a person who had a simular concern . He also had snow melt on the roof Finnaly he went to the spot under the snow melt pulled back insulation found a 3inch hole in the attic some one had left all the way to basement in centre of wall . Roy


  33. #33
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    Smile Re: Frost in the Attic

    In reply to Chis's question about moisture in a crawl space, and in conjucntion to Roy's reply concerning the stack effect, which is indeed a real phenomena in a home. It is my opinion that properly installed vapor barrier in a crawl space is one of the most important items in home construction. Even if for no other reason than to keep soil odors from drifting up into the home in well drained gravel area's. Not only that it keeps the home inspector cleaner after checking out the crawl space.

    As far as the ventilation goes I should have made one issue very clear, under no circumstance for moisture elimination do I suggest mechanical ventilation, as far as that goes I never suggest mechanical ventilation in an attic area, a crawl space is a totally different matter. It has been my experience that the largest percentage of power ventilation in attics never get serviced and are not operational at the time of inspection. Secondly mechanical ventilation is designed to work in the summer with their thermostatic controls and will not turn on in the winter months due to lower attic temperatures. Passive ventilation in the correct amounts is vitally important in an attic to allow moisture laden warm air which has already passed through the thermal insulation layer in conventional attics. At that point this additional heat and moisture in an attic becomes your home's worst enemy. Adequate ventilation in an attic is also the biggest factor in eliminating ice damming and related problems. This again is a proven Fact. To not install ventilation into an attic in a colder heating climate such as Minnesota, Idaho and Washington is a serious mistake. Roofing material life has proven to be extended with proper ventilation. One item not accounted for in modern building codes in the installation of black roofing shingles. It is not uncommon for me to encounter truss chord temperatures in the summer of as high as 165 degrees F. A lack of ventilation only makes this worse and a roof will constantly expand and contract which also breaks the sealing of shingle tab's and allows for higher rates of shingle blow off primarily with three tab shingles.

    It's a free world advise your clients as you wish, I so choose to advise mine in a manner which will help them maintain a home in good condition.

    TCS HOME NSPECTIONS
    Knowledgeable and Thorough

    PS: If properly installed combustion air,and or ventilation makeup air is installed in a home, and air leakage is controlled from within the conditioned area of a home this stack effect, if present should be minimal.


  34. #34
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    Default Re: Frost in the Attic

    With the increased amount of "tight" homes being built,,combustion air is the single most cause of air infiltration. Without proper introduction of combustion air to any fuel burning equipment ,the risk is there for infiltration from unwanted areas.


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    Default Re: Frost in the Attic

    Great group good discusion . Big help to many and many thoughts traded . Thanks to all... Roy


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    Default Re: Frost in the Attic

    Quote Originally Posted by Roy Cooke sr View Post
    ("Your attic looks pretty well ventilated but you may want to consider a fan hooked to a humidstat. //Rick ")

    I think I would be carefull in adding a fan exhaust as this could lower the pressure in the attic and cause more of a problem by drawing More warm moist air from the home .

    I expect not to far in the future we could stop venting attics ,it is done with some homes now and they did not vent homes many years ago.

    Roy Cooke
    Is there a way to mechanically vent attic space by adding air instead of exhausting air? A fan in the soffit maybe? Maybe this has not been done for good reason; I just can't think of that reason now. If the attic is sealed from the living space this won't be necessary of course but older houses that were insulated without being able install a vapour barrier might benefit.
    Any thoughts on that?
    Thanks.


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    Default Re: Frost in the Attic

    Pressurizing your attic will only make things worse,,to exhaust attic air will supply new air thru soffits or ridge vent or gable vents, Air changes in attic space are critical to moisture removal


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    Default Re: Frost in the Attic

    Quote Originally Posted by David Bell View Post
    Pressurizing your attic will only make things worse,,to exhaust attic air will supply new air thru soffits or ridge vent or gable vents, Air changes in attic space are critical to moisture removal
    Either way will exhaust attic air. The one way by creating a negative pressure which will "suck" air through places like the soffit and exhaust them through the fan. The other way by creating a positive pressure by pushing air in through the soffit and exhausting it through the roof, gable, or the other soffit vents. The advantage I can see with the positive pressure is that the moist house air will not get forced into the attic.


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    Smile Re: Frost in the Attic

    Quote Originally Posted by Bert de Haan View Post
    Either way will exhaust attic air. The one way by creating a negative pressure which will "suck" air through places like the soffit and exhaust them through the fan. The other way by creating a positive pressure by pushing air in through the soffit and exhausting it through the roof, gable, or the other soffit vents. The advantage I can see with the positive pressure is that the moist house air will not get forced into the attic.
    Be careful with fans in the attic area especially the size of fan. If the living spaces are not air sealed properly, can lights, cantilevers, penetrations, etc you can very well depressurize the attic and living area cause backdrafting, decrease energy efficiency. Just my thought/theory.

    What about the idea of consulting an energy rater to test the home?

    Michael Carson
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    Default Re: Frost in the Attic

    Quote Originally Posted by Bert de Haan View Post
    The advantage I can see with the positive pressure is that the moist house air will not get forced into the attic.

    Correct, but the outdoor air will now be forced down into the living space, taking all of its moisture, cold, etc., with it.

    The LAST THING you want to do is to pressurize the attic, right next to that is to de-pressurize the attic with an exhaust fan (that will have other unintended consequences, such as sucking the conditioned air out of the house) ... you want the attic to be relatively neutral and as close to outdoor pressure as can be, and for the house to be slightly (but not even that noticeably so) ... ... pressurized in relation to the outdoors (and thus the attic).

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    Default Re: Frost in the Attic

    Quote Originally Posted by Michael Carson
    Be careful with fans in the attic area especially the size of fan. If the living spaces are not air sealed properly, can lights, cantilevers, penetrations, etc you can very well depressurize the attic and living area cause backdrafting, decrease energy efficiency.
    I understand but I am asking about fans blowing air INTO the attic. This would pressurize rather than depressurize the attic. It could force some cold (and dry) air into the living area but that is not as big a deal as sucking warm (and moist) air into the attic. Both ways is a decrease in energy efficiency though.

    Quote Originally Posted by Jerry Peck View Post
    Correct, but the outdoor air will now be forced down into the living space, taking all of its moisture, cold, etc., with it.
    Up here in the great white North there is very little moisture in the air during the winter so theoretically having a positive pressure in the attic would be less harmful than having a negative pressure. Air from the house interior leaking into the attic will add moisture to the attic.
    I'm not trying to be argumentative but I am just trying to learn.
    Thanks


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    Default Re: Frost in the Attic

    A correctly vented attic is almost always in a negative pressure due to winds and the natural draft effect,,to pressurize it is to keep it from doing what it is meant to do.


  43. #43
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    Smile Re: Frost in the Attic

    Hello Bert

    Great question, but I believe David was right on the money with the air exchanges being the key idea in attic ventilation. To fully understand attic ventilation is to understand the reason's for venting an attic. Seasonal needs will basically change the reason for venting an attic. Eliminating unwanted heat in an attic in the summer to supplement a cooling system is as important as venting super heated air prior to producing condensation in the attic in the winter months.

    To more fully answer your question about mechanically venting an attic by inducing air into the soffit. This method of ventilation would not accomplish any more than having a mechanical roof top ventilator with no soffit ventilation. This is the reason that the building codes are specific as to where and how much ventilation needs to be installed in soffits, and upper elevations of the roof decks.

    I had the opportunity this past year to inspect a LEED certified home in Sun Valley which had an air to air ventilation system installed, with the heat exchanger unit installed in the attic. The builder had used a full closed cell foam insulation system blown onto the roof deck and upper truss chords (7 inches thick). The upper floor system was a singular truss system which included the floor deck, upper floor exterior and interior wall, and roof frame. The entire outer shell of the structure was sealed and insulated with this closed cell foam. The air exhchanger unit circulated the air for the entire attic space, upper floor, and main floor living area. In this manner the air exchanges for the entire home, and the indoor air pressures were strictly regulated. This is fairly easy to do in new construction, and with the correct understanding of indoor air pressures, and needed air exchanges in a home, with enough work and ingenuity you can somewhat accomplish the same idea with nearly any home. The first step in my opinion would be have a duct blaster test of your forced air system (assuming that is the case), and secondly have a quality blower door test of the home. You can't fix what you do not understand. If a crawl space is involved I would also suggest having the foundation perimeter walls and rim joist area sealed with a closed cell foam, a quality vapor barrier installed, and topped off with a proper conditioned crawl space ventilation system. These are in my opinion the foundation steps to controlling/ understanding indoor air pressures in home/ structure.

    I am sure I have not answered a single question but possibly I have allowed you to expand the horizon of what a simple attic ventilation question can possibly lead to. My favorite expression is that "it is easy to criticize that which you do not fully understand". Really of no relevance in this discussion, but some times it can be bent to enter any conversation.

    Air movement in a home is indeed a science, one that admittedly I have not mastered but I enjoy trying. The photos above are taken in the attic area of the home in Sun Valley I referenced.

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    Default Re: Frost in the Attic

    Quote Originally Posted by David Bell View Post
    A correctly vented attic is almost always in a negative pressure due to winds and the natural draft effect, ...
    Due to the natural draft effect and the winds, an attic is ... basically neutral as one area has a higher pressure (the windward side) and another has a lower pressure (the leeward side), making the interior of the attic have varying degrees of pressure, but overall on, on balance, it should be (if one could average the pressures out) at the same pressure as the outdoors (where the pressures are changing anyway).

    ... to pressurize it is to keep it from doing what it is meant to do.
    Agree with that 100%.

    To depressurize the attic does the same thing.

    Yes, one can pressurize, or depressurize, the attic and *MAKE* it vent, but there are consequences to those actions which one probably would not like in a modern, insulated, and somewhat sealed house.

    Jerry Peck, Construction / Litigation Consultant
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    Default Re: Frost in the Attic

    I just saw this in a house about a week ago. The soffit vents in the attic were blocked with insulation. The roof had soffit vents and gables. I told the buyer he needed to pull the insulation about a foot away from the the soffit and should upgrade to a ridge vent.

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    Default Re: Frost in the Attic

    Thanks a lot guys! Very helpful.


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    Unhappy Re: Heavy frost in the Attic

    Hi Everyone,

    I need your help! I have just discovered massive frost in my attic. RH in the home is around 28-40% depending on the day (with occasional spikes to 50) at a temperature of approx. 70 to 77 degrees C. This is a townhome/condo end unit. Insulation is fiberglass pink and there appears to be a vapour barrier beneath.

    You can see from the photos the frost is thick throughout the roof area.

    My questions are as follows - what should I do about the frost there now? It's going to melt and then what?

    What is causing it? Looking around the attic I can see the bathroom vent goes out through the roof. The furnace (natural gas) and hot water tank share the another vent out the roof. I can see a rectangular hole in the roof that may lead to a vent but an unable to see light there. There is soffitt around the outside of the roof (I will check to see if it's blocked). There is a reverse flow furnace in the house(hot air leaves via the bottom) with the cold air runs above it and a vent that seems to pull air from the attic into the run (is this normal?).

    What should be my first step in this?

    Thanks,

    Gerry

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    Default Re: Frost in the Attic

    I do not think you have enough frost to be concirned about the water from it.
    Yes it is not a good thing .
    I do think it is very cold in your area at this time .
    I expect you have warm home air getting into the attic .
    Is the access door Properly insulated & gasketed and is and is the door heavy enough to stop air from the house getting up there .
    A simple quick fix this time of the year is to get some stripable caulking and caulk the door if this is where air is getting to the attic.
    Next warm season strip the gasket and fix the attic entrance properly .

    Roy Cooke Royshomeinspection.com

    Attic Venting, Attic Moisture and Ice Dams | CMHC

    Last edited by Roy Cooke sr; 01-01-2010 at 05:50 PM.

  49. #49
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    Smile Re: Frost in the Attic

    Hello Jerry

    There is enough moisture/ frost in that attic to cause a black mold problem. Ventilation in a adequate amount is needed to allow the warm moist air to escap from the attic. As mentioned earlier a couple of times in this discussion on attic frost "any warm air when cooled in an attic will condense". As the warm air cools it will condense and deposit the condensation onto the attic sheathing as it is the coldest portion of the attic. Note in your photos that this frost extends fully to the peak of the attic. Normally this condition will begin at the lower portions of a roof slope and work its way up. The installed insulation is a fiberglass bat, and will allow for heat loss from the conditioned space. This warm air will condense as it cools. A normal family of five will deposit up to 5 quarts of moisture into the air every day from bathing, breathing, cooking, etc. Spill 5 quarts of water onto your floor and get a visual of how much moisture is involved. Without venting this warm moisture laden air out of your attic where else does the moisture have to go. At this point you have a moisture source, a wood cellulose sheathing, and an attic temperature which will support mold growth (not to mention the billions of mold cells common to all air sources. I suggest you control indoor moisture sources as well as possible, your 25 to 45 % RH is not considered high. I suggest that you properly vent the soffits and ridge line of the attic space. Additional insulation tightly installed to an R-38 or more will also make some difference. A good test will check your window surfaces in the home. If you are not showing excessive frost buildup in the windows or aluminum sliding door or window frames, this is simply a lack of ventilation in the attics in a normal home.

    Prior to becoming a home inspector my father in Law and I operated an insulation company, and I have personally insulated hundreds of attics, and as a home inspector have been in thousands of attics. This attic is simply under ventilated. Ideally you want the interior attic temperature above the thermal insulation level to be the same temperature as the exterior. With heat loss from the conditioned space this obviously will never occur. Hope this helps.


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    Default Re: Frost in the Attic

    Sorry! I ment to address the last post to Gerry.


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    Default Re: Frost in the Attic

    Being Calgary and it is cold I do not think you need to worry about Black mould.
    Stopping the warm moist home air to the attic is what you need to do .
    Adding more ventilation can just increase the air from the house.
    The first warm sunny day will get the frost gone from the sheating.
    Go to some of the CMHC places I have posted and see.
    I can send you more information if you want.
    Look for elect boxes or flush ceiling lights that could be leaking air .
    Stop the air leaks and concirns will be gone .
    Roy Cooke ... Royshomeinspection.com


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    Default Re: Frost in the Attic

    I've read in the past, but no longer can find that information or link to it, that Minnesota had testing done which showed that fiberglass insulation, especially loose fill, but fiberglass batt to a lesser degree also, suffered a loss of R-value of up to 50% in extreme cold climates such as the winter temperatures in Minnesota.

    I imagine that Canada would be a similar, and possibly worse, environment as to cold temperatures.

    That R-value loss could be coming into play with frost in the attics as it allows for a greater air attic air temperature in the attic air which is closer to the ceiling, with the temperature falling more rapidly the closer to the sheathing you get.

    That means the air in the attic could contain more moisture escaping from within the living space below, then condensing out (which causes the frost) on the colder sheathing.

    Regardless, though, the cause is the moisture in the air, and the most likely source for that moisture is from inside the living area, and the reason that moisture is in the attic is excess leakage - air exfiltration - from the living space into the attic.

    The first solution I would recommend would be to have a contractor go into the attic and move the insulation away from all the wall top plates, ceiling lights, etc., anything which penetrates into the attic from below, sealing up ALL gaps and spaces around EVERYTHING, then moving the insulation back into place. That would be the first step in reducing the moisture load in the attic, which may well bring the condition under control, but this will still solve and reduce many other problems, and save energy as every gap and space sealed is one less gap or space where conditioned air - which costs money to condition - can escape to the attic and be lost as wasted energy.

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    Default Re: Frost in the Attic

    Quote Originally Posted by Roy Cooke sr View Post
    Being Calgary and it is cold I do not think you need to worry about Black mould.

    Some people always jump onto that mould wagon as the first thing to worry about, when there really is no, or very little, to worry about with regards to mould in the house, especially when in the attic.

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    Default Re: Frost in the Attic

    Quote Originally Posted by Jerry Peck View Post
    Some people always jump onto that mould wagon as the first thing to worry about, when there really is no, or very little, to worry about with regards to mould in the house, especially when in the attic.
    Thanks Jerry .
    Exactly every home has Mould . I just removed some pudding from my Fridge and it had some on top.
    Fiberglass is just a big filter

    Some interesting reading below ... Roy

    http://www.buildingscience.com/documents/reports/rr-0209-mold-testing/view?searchterm=mold

    http://www.cdc.gov/mold/dampness_facts.htm

    http://www.epa.gov/mold/moldguide.html


  55. #55
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    Default Re: Frost in the Attic

    Put in a ridge vent, make sure there are no exhaust fans exhausting into the attic, make sure the attic floor is fully insulated with a vapor barrier facing the sheet rock on the attic floor not on the outside, other than that not much more you can do. If the humidity is high outside and the temp is below freezing what do you expect the moisture in the air to do, it is just like when it frosts in your yard, no difference


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    Default Re: Frost in the Attic

    Quote Originally Posted by Cobra Cook View Post
    Put in a ridge vent, make sure there are no exhaust fans exhausting into the attic, make sure the attic floor is fully insulated with a vapor barrier facing the sheet rock on the attic floor not on the outside, other than that not much more you can do. If the humidity is high outside and the temp is below freezing what do you expect the moisture in the air to do, it is just like when it frosts in your yard, no difference
    0°F here this morning No way do I want to put in a ridge vent now.
    Vapour Barrier is code now .
    Old home I would not be to concerned as two or more coats of paint do the job . My attic has no frost this morning but my car is covered .
    I do not think outside humidity effects the attic much .
    We had big fog yesterday morning .
    I am also of the feeling to much attic ventilation is not a good thing.
    Royshomeinspection.com


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    Default Re: Frost in the Attic

    I saw no obvious venting at all,,if ridge vent is not possible at least cut in some high gable louvers on opposite sides


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    Default Re: Frost in the Attic

    Quote Originally Posted by Jerry Peck View Post
    I've read in the past, but no longer can find that information or link to it, that Minnesota had testing done which showed that fiberglass insulation, especially loose fill, but fiberglass batt to a lesser degree also, suffered a loss of R-value of up to 50% in extreme cold climates such as the winter temperatures in Minnesota.
    Do you mean because of air infiltration because of windwashing or some thing that just applies to Fiberglass?


  59. #59
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    Default Re: Frost in the Attic

    This thread makes a pretty good argument for the sealed, insulated, spray foam (directly to the roof deck) attics.


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    Default Re: Frost in the Attic

    Quote Originally Posted by chris mcintyre View Post
    This thread makes a pretty good argument for the sealed, insulated, spray foam (directly to the roof deck) attics.
    I was asked to assess some relatively minor repairs to be made to a roof structure. (Not as HI but as contractor.) This was in a livestock housing facility so moisture is more of an issue than in attics.
    Anyways, the -minor repair- turned into -not worth repairing.-
    Everything from the foam insulation on up was rotten, sometime so badly rotten that all there would be left of the purlins spanning the trusses was a small pc stuck on a nail or something. Every thing below the insulation was still fine.
    Obviously the foam absorbed the moisture and the wood work stayed moist continuously. Sealed, closed-cell shouldn't do this but it scared the bejeebies out of me. I have seen foam insulation around windows that had enough water in it, it could be squeezed out so some foams do absorb moisture.


  61. #61
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    Default Re: Frost in the Attic

    ....that all there would be left of the purlins spanning the trusses....
    I'm assuming this was a metal roof. On a roof with OSB and fiberglass shingles where the foam is sprayed against the roof deck at least 8" deep(with open cell) and the felt and shingles are on the other side, I would think that without an irrigation system installed in the attic that it would be nearly impossible to get enough moisture in the attic to rot the sheathing. Just my opinion.


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    Default Re: Frost in the Attic

    Quote Originally Posted by Bert de Haan View Post
    I
    Anyways, the -minor repair- turned into -not worth repairing.-
    Everything from the foam insulation on up was rotten, sometime so badly rotten that all there would be left of the purlins spanning the trusses was a small pc stuck on a nail or something. Every thing below the insulation was still fine.
    Obviously the foam absorbed the moisture and the wood work stayed moist continuously. Sealed, closed-cell shouldn't do this but it scared the bejeebies out of me. I have seen foam insulation around windows that had enough water in it, it could be squeezed out so some foams do absorb moisture.
    I do not know I would say obviously ,
    I have seen foam under the sheating and every thing was fine I have also seen Rotten sheating where there was no foam .
    It to me might have been worn out shingles alowing water to penetrate and the foam stopped the water from getting into the space under the roof.
    Roy Cooke


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    Default Re: Frost in the Attic

    Quote Originally Posted by chris mcintyre View Post
    I'm assuming this was a metal roof.
    Yes it was.
    Quote Originally Posted by chris mcintyre View Post
    On a roof with OSB and fiberglass shingles where the foam is sprayed against the roof deck at least 8" deep(with open cell) and the felt and shingles are on the other side, I would think that without an irrigation system installed in the attic that it would be nearly impossible to get enough moisture in the attic to rot the sheathing. Just my opinion.
    You may be right.
    Quote Originally Posted by Roy Cooke sr
    I do not know I would say obviously ,
    I have seen foam under the sheating and every thing was fine I have also seen Rotten sheating where there was no foam .
    It to me might have been worn out shingles alowing water to penetrate and the foam stopped the water from getting into the space under the roof.
    Roy Cooke
    The roof covering wasn't in good shape but it wasn't in such bad shape to have this effect over the whole roof. Maybe I'm being a little quick with my -obviously- conclusion but it did scare me off enough to not put spray foam in my attic just yet.


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    Default Re: Frost in the Attic

    Quote Originally Posted by Bert de Haan View Post
    Do you mean because of air infiltration because of windwashing or some thing that just applies to Fiberglass?
    Because the cold air settles down into the insulation, slowly, but it does, and as it does settle down into the effective insulation thickness is reduced, which results in a respectively lower R-value.

    In climates which are not as cold (and not for as long) the temperature of the air in the attic and in the insulation has a chance to be re-warmed, which delays the settlement of the cold air.

    This effect is most pronounced in the much looser packed fiberglass of loose fill, however, fiberglass batt still allows for that process due to the air spaces between the fibers.

    Cellulose and other more dense insulation does not suffer from that same condition, or if they do the effect is negligible.

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  65. #65
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    Smile Re: Frost in the Attic

    Roy and Jerry

    With all due respect to your knowledge. I have read you posts for several months now and I do have respect for most of your opinions. This frost in the attic thing and your apparent lack of acknowledging the importance of attic ventilation in a cold heating climate is absurd. Yes moisture in the attic is coming from within the conditioned area's of the home. Yes a home owner should vent bathroom, kitchen and clothe dryer exhauststs fully to the exterior of the home. We went through a period of construction in the 70's and early 80's where builders were told the tighter you can seal up a home the better off you will be. Well it didn't work then either. Air exchanges in a home are important (don't confuse that statement with thinking I mean sealing ceiling light boxes and attic access's is not important, because it is).

    There is no difference in the mold on your pudding and the mold that is going to grow in Gerry's attic if it is not properly vented. It's easy to throw the pudding away. What's your answer for his attic when he goes to sell and Mr. Home Inspector comes along and says " gee what a nice home, with the exception of the black attic mold". It's time to either get off the high horse about not installing ventilation in an attic, or explain why it's just the rest of the world that is wrong. Mold propagation in an attic needs three things (just like your refrigerator) food source, moisture and the correct temperature. All three are present in an attic. The mold cells floating in the attic are simply waiting for a reason to propogate.

    You guys can run around with your caulking guns and tell everybody things will be fine. Personally I am going to wait for that special day and install some attic ventilation in my homes.

    Nobody else has denied that moisture comes from within the home, and that it can be some what controlled (but not 100%). Insulation R values are resistance to heat loss, which is greatest through a ceiling. Even R 60 insulation will eventually allow warm moisture laden air into an attic.

    Lets give these guys reading these posts the benefit of our combined experience and recognize the value of ventilation for what it really is.


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