Potential condensation concerns with unvented roof assembly
I had a post earlier this year about a unvented roof that I planned to have installed. I couldn’t figure out how to continue that post/system wouldnt let me reply on it. However, this post should contain most all the relevant information.
Having had this roof installed in August, The house has been very warm, and now requires very little to heat it compared to last year (much colder winter this year too), so it’s great from an insulation standpoint. However, I have what appears to be a condensation related issue.
A few things changed with the roof design. The cavities were dense packed with cellulose, and the bay’s were closed up with 1.5″ polyiso and canned foam at the top plates.. One layer of 3″ polyiso on the roof, with taped seams and good attention to tight seams and foamed penetrations.
House has 4′ overhangs. We ran the 3″ polyiso about 2.5′ past the walls. Thinking this would help with heat under the soffits, and against house during the summer. I have noticed moisture originating around the screws that hold the polyiso to the sheeting (this is past the walls in the open air soffits) Not all the screws are doing this, but some even drip moisture, and it seems to wick out from the screws. Sometimes 4-6″ out parallel to walls. But I can check a wet spot a day later and it’s almost completely dry.
The screws/areas doing this are about 1-2′ past the house walls, exposed to cold from below. It has been dry, no rain. Outside humidity around 60-70%. Outside temps have been in low to
Mid 30’s. My biggest concern, is that this could be happening within the sealed roof/building envelope?
I pulled blocking in a bay to look for moisture, seems nice and dry, but being packed with cellulose, i couldnt see any screws. I’m not happy with the blocking the insulation company did, they wedged the polyiso in fairly tight between rafters and tried to foam the edges or small gaps. I plan to closed cell spray foam to seal the existing blocking once the temps warm up enough.
It is possible that some heat escapes passed the blocking in some areas, but I don’t see this causing the moisture 1-2′ past at these screws, where they penetrate the sheeting. Is heat getting past the blocking and top plates, reaching the cold roof decking and condensing? Would this not be happening within the closed roof system also?
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