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Old 01-29-2012, 12:22 PM   #1
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excessive moisture in attic crawl space


Yesterday I went and helped my buddy put a ceiling fan in. While crawling through his attic crawl space. I noticed excessive moisture. Everything seemed to be wet. The plywood on the roof and the insulation. Not wet that it stained the sheetrock below. Just "moisture". We went up on the roof and I couldn't find any issues. While it did look like he'd need new shingles in a few years, they weren't totally shot. I'd estimate he needs new shingles 5 years down the road, but I'm no expert. When on the roof we saw dark areas that seemed to coincide with the wet areas I saw below. But the dark areas were only on one side of the roof. I checked his attic ventilation and while it seemed to be low it wasn't ridiculous. I think it was 3 vents by the peak, continuous soffit vents and one gable vent. I left his house confused with no good explaination for him. With time to think about it, I thought it might be his exhaust vents for the dryer and bath fans. He ruled out the dryer exhaust. He's supposed to check the bath fans exhausts. Are there any other good explanations for a lot of moisture that I could have him check?

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Old 01-29-2012, 01:14 PM   #2
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excessive moisture in attic crawl space


Is this a finshed attic?
Was there insulation laying out over the soffit vents?
Was there room for air flow over the top of the kneewalls.

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Old 01-30-2012, 08:02 AM   #3
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excessive moisture in attic crawl space


+1 to Joe's questions.

Questions
  1. Ventilation
  2. Bathroom fans and moisture control
  3. Crawl space condition and set up
  4. Insulation depth and type
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Old 02-06-2012, 12:05 AM   #4
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excessive moisture in attic crawl space


Going from memory here. There was not insulation over the soffit vents. It is not a finished space, it is a crawl space. I remember thinking the insulation was on the low side. Maybe somewhere around 8" thick. Fiberglass batts. Ambient temperature this time of year ranges anywhere from 30 to 50 degrees. I Have told him multiple times to check his bath fans exhaust, but he didn't understand, i guess. Or he didn't believe me, hes not mechanically inclined. He took my advice and stuck 3 large box fans up there and he said the moisture is "much better, but it hasn't been raining" He is still convinced its coming through his roof, even though there is no drips or obvious leaks.


After thinking about this, the only logical thing i can think is his bath ran exhaust. If every time he showered it was blowing all the steam up there, it would make a ton of moisture. I can't come up with any other logical scenarios. Im not talking about a little bit of moisture here..........
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Old 02-06-2012, 12:12 AM   #5
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excessive moisture in attic crawl space


If there is no free air flow over those knee walls, soffit vents that are not blocked up and a ridge vent on the peak of the roof then there's going to be a moisture build up.
And also a way for that bathroom vent to vent out the roof.
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Old 02-06-2012, 12:32 AM   #6
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It could easily be the bath fan exhaust. If not, check the walls below the 3 really wet spots for air leaks under the fiberglass. Moisture is coming up : through a vent/drain plumbing pipe over-sized hole, or a large wiring/HVAC hole possibly from the furnace room or even connected to the basement/crawlspace. With the "stack effect"-- either mechanically or natural: http://www.wag-aic.org/1999/WAG_99_baker.pdf

The moisture rises through the insulation and collects on the closest "condensing surface"-- the roof sheathing; http://www.buildingscience.com/docum...bout-diffusion

Check the wetness of the insulation there. Also look at the color of the f.g. for air-leakage signs: http://www.finehomebuilding.com/PDF/Free/021105092.pdf

The attic may need air sealing; http://www.familyhandyman.com/DIY-Pr...s/Step-By-Step

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Old 02-06-2012, 12:35 AM   #7
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Quote:
Originally Posted by joecaption View Post
If there is no free air flow over those knee walls, soffit vents that are not blocked up and a ridge vent on the peak of the roof then there's going to be a moisture build up.
And also a way for that bathroom vent to vent out the roof.

i have no idea what you just said........ The soffit vents had air flow to them. There are vents on the peak............ What knee wall?
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Old 02-06-2012, 01:04 AM   #8
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excessive moisture in attic crawl space


You keep saying crawl space. A crawl space is the area under the house when there's not a full basement.
The short walls in an attic are called knee walls. I'm not even sure the area behind them even has a name but it's not crawl space.
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Old 02-06-2012, 01:31 AM   #9
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Quote:
Originally Posted by joecaption View Post
You keep saying crawl space. A crawl space is the area under the house when there's not a full basement.
The short walls in an attic are called knee walls. I'm not even sure the area behind them even has a name but it's not crawl space.

oh, sorry for the confusion. When i said crawl space, i meant it is not a finished room and it has low headroom. Im 100% only talking about his attic. I didn't go under his house at all..... .I know what a knee wall is, i was just confused about why you were talking about them. Im just talking about standard trusses here with nothing breaking it up. I know it can be hard to follow without any pictures or anything. So i just drew you guys a doodle. Its not to scale There is a chimney that breaks up a good portion of the two sides. My hypothesis is that the bathrooms vent is causing moisture on the one side, and the chimney is keeping the two sides somewhat separated
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Old 02-06-2012, 01:46 AM   #10
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excessive moisture in attic crawl space


Not even close to enough venting out of that roof.
There needs to be ridge want across that whole roof to within a 12" of the ends.
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Old 02-06-2012, 06:48 AM   #11
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excessive moisture in attic crawl space


Needs more venting and you have to get the bathroom moisture through the roof deck.
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Old 02-19-2012, 03:46 AM   #12
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finally had a day off and went in my buddys attic. I found that all 3 bath fans very hoakily rigged and one vent was completly disconnected. Im 100% sure that was his problem. I didn't have time to fix it for him so hopefully he gets it taken care of. I have a feeling he might be intimidated so he won't tackle it. Oh well, ive done my share. The good news is that with his access hole, from the garage, left open and fans going, it was dry as a bone up there

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