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TOPIC: Underlayment

roof sweating

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So I am putting on a new copper standing seam roof. 2x6 sleepers over the existing roof, then filled with foam insulation, then plywood, hi temp underlayment. Still to come will be slip sheet, then the copper, but since the self stick underlayment was installed we are experiencing sweating. The insulation contractor assured us this wouldn't happen. There are no roof vents, and it is a gable. Any remedies?
joe cccaa

5/6/2010
By foam insulation you mean a rigid foam? What part of CA are you in? Pictures? Where is it sweating?
Eric Novotny
An informed customer is the Best Customer!

5/8/2010
sprayed in foam; hardens like concrete. Central california, right on the water. Its sweating in the light cans, but on the upper side of them. I think it may be coming from the inside, as they are laying tile, & it is quite humid inside. No pics yet but i'll see what I can do.
Guest User

5/8/2010
Spray foaming the roof has nothing to do with the light cans as they are connected to the attic. If you have high indoor humidity and a cold attic (at leas as cold as outside) which you do not because of the insulation on the roof deck and lack of transferred heat from the sun, you will have condensation where warm moist air meets cold. If anything, this is showing that your insulation and new roof is doing a good job of keeping the heat out of the attic and now your attic is cold. Are there any vents in the gable ends? Do you have attic access? The long and short is that the attic probably needs to be air sealed and some enclosures around the can lights to bring them back into the building envelope.
Eric Novotny
An informed customer is the Best Customer!

5/9/2010
I'm sorry I didn't make this more clear; there is no attic space. It is a vaulted wood ceiling, with sleepers added on top for the insulation. Therefore the light cans are within 1/4" of the plywood on top. The insulators then sprayed in foam between the sleeper rafters, & up to and around the sides of the light cans. The cans are approx. 12" square. We were thinking the 1/4" gap may have had adverse effects so we hole sawed in center of one & added more foam.
Guest User

5/9/2010
If the indoor humidity is not out of whack, then you have unconditioned air entering the interstitial space between rafters (framing). You have a good thermal break as a result of the foam that is now keeping the rafter air space much cooler. Warm moist air is migrating from the living space and is contacting that cool air. Result...condensation. Ideally, the area around the lights could have been cut on the roof deck and enclosure built around them at that point. Other option to to just seal everything (eaves, ridge, etc) in the old roof deck that you can get to.
Eric Novotny
An informed customer is the Best Customer!

5/9/2010