Dripping outside
10 year old home, north central Mn. vaulted ceiling. We had trouble with inside dripping due to improper venting in the small attic space. We removed all the car siding from the ceiling and removed the over stuffed fiberglass. We sealed up all ventilation and spray foamed the ceiling with closed cell foam making a hot roof. Now this winter we have dripping on the outside of the house. We removed car siding from the interior walls and cut out a piece of OSB out so we can see into the soffit. It was full of frost! We also found frost on the inside of the OSB. All construction looks proper, tight and sealed. From inside to outside – Knotty Pine, vapor barrier, 6″ fiberglass, OSB sheathing, Tyvek wrap, vinyl siding.
if we have an air and vapor leak, we can’t find it! we are running our exhaust fans and lowering the interior humidity level. We’ll see if that helps. Any other ideas?
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The problem is likely the vapor barrier. It is blocking vapor just fine, but it is very hard to get the detailing right to make it an effective air barrier. If interior air flows into the cavity, the moisture it carries will condense and freeze on the sheathing.
Given that there have been no major changes in the wall assembly, this has probably been happening every winter. If there are no signs of water damage, then you can probably ignore the issue. When it warms up, the water is drying quickly and leaving the assembly.
If you do want to fix it, you have two options. The first is spray foam, much like you did with the roof. Make sure you meet the minimum thickness requirements for your region. The alternative is to remove your siding and add exterior rigid board over your sheathing (again, at the right thickness).
Dave,
Almost every home that uses boards as the interior finished surface (instead of drywall) has this problem. Your wall lacks an air barrier.
Air barriers aren't optional!
Once everything dries out, the solution is to install taped drywall as your interior air barrier, and then install boards on the interior side of drywall (assuming you aren't so angry at your boards that you don't just prefer drywall).
HI Dave -
Until I actually SAW the air leaks in what I thought were well insulated and sealed building assemblies, I simply did not believe they were not airtight. You see the leaks during a blower door test, especially one augmented with an IR camera.
Get a blower door test done on your home; that will be proof positive.
Peter