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Old 02-10-2009, 10:24 AM   #1
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Frost in Attic


I have such high humidity readings in my attic in the winter time. 68%, 73%, 70%...If it is a really cold night, 8 - 20 degrees, I will check the attic in the morning and their is frost all over the nails and sheathing.

I thought I solved the problem when I put a whole new roof system in. Ridge Vent, and extended my roof line to put in 12 inch soffits to get perfect soffit to ridge venting. (I closed up my gable vents - I have done a ton of research on this) But it still is not working.

Why am I getting so much humidity in my attic. Could it be that my insulation is poor and there is that much heat loss. If so, why is the heat not escaping through the ridge. I live in a 2 story colonial built in 1967 in Long Island, NY. All new siding and anderson windows etc. Any ideas?


Last edited by Ed the Roofer; 02-11-2009 at 05:44 PM. Reason: I couldn't read the micro-sized small font.
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Old 02-10-2009, 02:56 PM   #2
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Frost in Attic


Quote:
(I closed up my gable vents - I have done a ton of research on this)
Not quite enough research:
http://roofingcontractorreview.com/R...cuit-Myth.html

That said, there could be a few reasons.

Is there enough soffit/ridge vent net free area for the size of the attic?
Is the ridge vent installed properly?
Are the soffits blocked? http://roofingcontractorreview.com/S...ntilation.html

Hard to say without being there. Pictures?

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Old 02-11-2009, 05:46 PM   #3
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Frost in Attic


How much humidity do you create inside of your home?

Is there any bathroom or kitchen fans that are exhausting directly into the attic?

What R-Value and how old is the current insulation?

Could be several reasons, but something is creating the excess RH content. That is too uch for a natural ventilated condition.

Ed
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Old 02-12-2009, 09:08 AM   #4
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Frost in Attic


....all the different theories on soffit to ridge venting with or with out gable venting can be a bit confusing. The theory by removing the gable vents FORCES the cold air through the soffit to the ridge and out the ridge. (But I know you guys have heard all the theories in the world) what to believe? I do not know anymore. However, I did see an improvement in the frost when I did close the gable vents. I have tried it both ways. Nothing is blocking the soffits, I can see the light of day on each bay. The actual soffit consist of vinly with many, many holes in it with no plywood above it, so it should be breathing well. I did think my roofers may have hammered down the ridge vent too much. They used that strip of "SOS brillo" pad material and than hammered in the ridge roofing material on top. I felt that the ridge vent material was so smooshed down it was not breathing right, so I took my wonder bar out and lifted the nails a 1/4 inch or so just to raise it up a bit. As for the insulation, it is very old looking, the first layer of insulation has that very thin vapor barrier material on both sides and when I touch it, it just falls apart. Prior owner than must of had other insulation put down on top of the old stuff, with no paper on either side of it, just pure insulation. Can insulation really go bad? Is it worth it for me to have someone remove all the insulation and than put down new? Attic is 20 X 40 and about 4.5' at the peak. Wife does run 2 humidfiers per night in the kids room, however the rh in the rooms still read about 30%. I have had readings of 10 degrees outside at 30% rh, 31 degrees in attic w/ 71% rh and 30% rh inside. I have been working on this problem for over 6 years and I am ready to move.
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Old 02-12-2009, 08:28 PM   #5
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Frost in Attic


I, too, re-did my ventilation similar to yours. I have a circa 1963-64 built colonial house with a gable roof. However, I do not have soffit overhang, so I installed SmartVents at the eaves instead. Also have a continuous ridge vent. It is the Cobra mesh type. I think that I will be changing that out to a baffled vent since they are suppose to work much better.

I boarded up and sided over my old gable vents.

Prior to doing this, I had frost underneath all of my sheathing and nails. This year, the frost was virtually eliminated except in a few areas.

What I also did do was removed the old mineral wool insulation that was in the attic, air sealed as many penetrations that I could reach with spray foam and caulk. It was impossilbe to reach toward the eaves to seal, so the exterior wall top plates aren't sealed. I then installed all new insulation up to a value of R-49. R-19 between the joists and R-30 perpendicular with rafter baffles installed.

I am still getting light condensation/frost along 1 gable wall, but that is also where my pull-down attic stairs are located, so I think that humidity is sneaking in that way, although I've sealed the stairs and framing up as best as I could.

I try to keep the house around 30% humidity during the winter.

I've been up and down the attic several times this winter. I know each time dumps more warm humid air into it.

There are times that I had high RH readings like you --- 60-70%, but that matched my outdoor readings. There were instances when the outdoors was close to 0F with 80-90% RH! In addition, there was a heavy snowfall on the roof which completely covered and blocked my ridge vent.

In your case, if the attic RH is high, but the outdoors is much lower, I'd start by looking to seal up bypass leaks in the attic -- ie -- electrical bypasses, plumbing stack, HVAC, tops of wall plates, etc. From what I've researched, a lot of warm humid air can sneak in via these bypasses regardless of how much insulation is installed. There is a wealth of info on the internet regarding air sealing the attic space. Of course, with proper ventilation, the humid air "should" escape.

Just my opinion.

Last edited by cougar01; 02-12-2009 at 08:31 PM.
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Old 02-13-2009, 01:21 PM   #6
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Frost in Attic


Also look for natural sources of humidity like untarped dirt in a basement crawlspace.
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Old 02-17-2009, 09:50 AM   #7
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Frost in Attic


Thanks for your feedback cougar01. Interesting that so many people have similar problems. I wonder how many other people that do NOT venture into their attic have a major problem and do not even know about it. This frost will than lead to mold. It is awful. I have a guy in my neighborhood, that has the same house as mine, w/ no soffits, no ridge vent and no gable vents. I would like to know what the hell is going on up in that attic. I also wonder if I have a problem because of how my house sits. I have a lower property than my neighbor to my left and right. I also have a big 8 - 10 foot retaining wall in my back yard that backs up to a sump. So my property sits so low, does that affect air flow...?? Just more things to think about. Thanks for the tip on sealing up all the leaks in the attic...especially around the pipes. I will get that can of yellow crap and spray in in there and see what happens. I also want to look into that baffle type ridge vent too!
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Old 02-17-2009, 11:18 AM   #8
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Frost in Attic


Quote:
Originally Posted by jlflynn1 View Post
I also wonder if I have a problem because of how my house sits. I have a lower property than my neighbor to my left and right. I also have a big 8 - 10 foot retaining wall in my back yard that backs up to a sump. So my property sits so low, does that affect air flow...??
And you don't have any uncovered crawlspaces in your basement? If your house is lower than the surrounding houses, the dirt your house is on is likely to contain more moisture than that under other houses.

Ultimately the humidity has to be coming from a source. It could be coming from the bathroom and the kitchen but an uncovered unvented crawlspace will transmit humidity into the house from the ground 24 hours a day. The best way to prevent condensation and frost problems in a house is to get rid of the source of the moisture if possible.

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