Walk-in attic moisture problem
My 50+ year old house has a walk-in attic that we use for storage. There is moisture on the roof decking and some mold in the winter. The soffits are vented, there are 2 gable vents and a roof fan. The mold is mostly on the side that faces north and is more toward the roof line than the peak. I have weather stripping on the door and have glued 1″ insulating foam board to the door in hopes of reducing heat entering the attic via the door. I have tried to seal off as many source of heat entering the attic that I can find. There is about 6 inches of insulation, not sure of the R value. I have tried running the attic in the winter and still see condensation.
Could the gable vents be functioning as intake and thus short circuiting the soffit vents?
I cannot abandon using the attic. It is not living space but we go up there daily to get stuff.
I am concerned that the moisture will ruin the roof decking over time.
What sort of contractor should I look for to help with this?
Suggestions?
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Replies
You should look for a home performance contractor... someone who can do a blower door test and air sealing work. The problem you have is most likely air leakage into the attic. Insulating the door is an understandable instinct, but the warmer the attic is, the less condensation will occur. Making the attic colder without reducing the air leakage can worsen the problem.
Morris,
David is right: this problem has nothing to do with insufficient insulation. The problem is air leakage from the heated area of your home into the attic. Common leakage areas include cracks near chimneys, duct penetrations, plumbing vent pipes, and bath exhaust fans. It's also important to seal the crack between the drywall and partition top plates.
Don't run your attic fan. It won't help solve the problem, and it may make your problem worse (by pulling more heated air through cracks in your ceiling). It also wastes electricity.
A few followup questions:
1. What about improving the ventilation in the attic? Should I seal the gable and roof fan and go with a ridge vent? Does ventilation play a role?
2. What about spray foam insulation underneath the sheathing?
3. I did not notice a problem until I got a new roof. My old roof had two layers of shingles, could the extra layer have provided some insulation in some way?
Morris,
The fundamental problem you need to address is air leakage. If you can address this problem, you will not only solve your attic moisture problem, you will save energy.
If, on the other hand, you try to solve your problem by increasing the ventilation rate, then (a) you will be spending money on a measure that won't save you any energy, and (b) the increased ventilation rate could even make your problem worse and your energy bills higher.
To learn more about attic ventilation, see the following articles:
Lstiburek’s Rules for Venting Roofs
Creating a Conditioned Attic
Are Solar-Powered Attic Ventilators Green?
Makes sense and I will find someone to do a leakage audit at least for the attic.
Any thoughts on why I did not notice this with the old roof that had 2 layers of shingles and no soffit vents but with the new roof with one layer of shingles and soffit vents added?
Morris,
Q. "Any thoughts on why I did not notice this with the old roof that had 2 layers of shingles and no soffit vents but with the new roof with one layer of shingles and soffit vents added?"
A. No, I don't know why you are noticing the problem now -- unless you have increased the indoor humidity in your home (for example, by running a humidifier) or unless you have altered your ceiling in a way that makes it leakier (for example, by installing new recessed can lights).