Damp underside of roof


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Old 03-27-06, 02:43 PM
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Damp underside of roof

A few weekends ago I was in my attic running some wiring for a project I was working on. When I was in the attic I noticed one side of the roof underside was completely damp.
I live in a 100 year old house in minnesota. The roof is a 45 degree pitch with one side facing north and the other facing south. It had snowed quite a bit the week earlier but it was fairly warm outside so much of that was melting.
The dampness was only on one side of the roof and extended over the entire undersurface. What is going on here? What should I do to fix the problem?

The roof is new as of 3 years ago. Except for a vent cap that was damaged in a nasty storm last year we have not had any problems with the roof whatsoever.

Thanks
 
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Old 03-27-06, 07:18 PM
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Sounds like improper or no attic space venting...... What you are seeing is condensation much like a tea glass "sweats" in the summer when warm moist air hits cold air....... I am betting you have very little attic venting.......
 
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Old 03-27-06, 09:31 PM
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I have a few 10x10 vent caps and one large 10x20 vent on the side of the house. How many should I have. I think the roof is about 12 square.
 
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Old 03-28-06, 10:24 AM
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Learn more about attic ventilation on this website at http://doityourself.com/attic/properventilation.htm

Make sure bathroom and kitchen vents, dryer vents, or any other type of appliance vent is vented directly into attic. Make sure vapor retarder was installed beneath insulation to prevent warm, moist air from passing into attic from the heated area below. Make sure you have stopped all air leaks from below.
 
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Old 03-28-06, 11:02 AM
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"Make sure bathroom and kitchen vents, dryer vents, or any other type of appliance vent is vented directly into attic."

Shouldnt this say are NOT vented directly to attic??

The minimum venting is figuered as the SQUARE footage of your attic are divided by 150. Example: your house is a 30' x 30' square. 30 x 30 = 900 square feet. Divided by 150 = 6 square feet of venting. Ideally you should use 300 as a divider instead to get good venting. In my example above then you would need 12 square feet of venting. You mention vents but not sizes or function. The 10" x 20" will only provide about 1.3 square feet of "free air" venting. My guess is you need more vents.
 
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Old 04-02-06, 08:47 PM
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I'm having a similar problem and was also told it was a venting issue. Our roof has two enclosed attic sections. The entire roof was done 12 years ago. One section is doing well, but the other is shot. I had a roofer (not the one who did the install) come out and asked him to determine the cause. He told me that the roofers put in an adequate number of roof vents, but they failed to close off the existing gable vents (on the attic ends), and this caused all the vents to be ineffective. As he put it, "they cancel each other out" so that little venting was actually taking place. The result being condensation and the plywood rotting.

I have no reason to disbelieve the guy, but I'm also too ignorant to know if what he's saying is even possible. Does his explanation make sense? Would having gable vents and roof vents both cause a venting problem?

Thanks in advance for your assistance.

Sidney
 
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Old 04-03-06, 11:05 PM
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I have never heard of vents "canceling each other". You may want to contact an HVAC expert. They are really up on venting requirements. H eating V enting A ir C onditioning
 
 

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