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Discussion Starter · #1 ·
Hi, Erwin- new to this forum.
have decades of construction knowledge, but I have tried everything for 10 years on my house. Garage, new construction, I used open cell spray foam on underside of Zip sheathing- been great
house was fiberglas- Cape with shingle roof. Ice backup many times. Ripped entire roof clean to 9/16 plywood- installed brand new metal after ice and water shielding. 5 years ago, I spray foamed- closed cell sprayed entire under side after I proper vented
just found another leak and saw water on underside of roof while renovating my upstairs bathroom
WHAT AM I DOING WRONG- THANKS
 

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Can't speak to your situation exactly not having seen it firsthand. But in the 30 yrs I've been doing residential re-roofs every single home that had foam (panels or spray) tight to the underside of the roof sheathing had issues with sweating (condensation), form just a bit of dampness to full blown rotted sheathing and rafters. Those homes the had good postive ventilation of the sheathing underside had little or no issues.
 

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Discussion Starter · #3 ·
Can't speak to your situation exactly not having seen it firsthand. But in the 30 yrs I've been doing residential re-roofs every single home that had foam (panels or spray) tight to the underside of the roof sheathing had issues with sweating (condensation), form just a bit of dampness to full blown rotted sheathing and rafters. Those homes the had good postive ventilation of the sheathing underside had little or no issues.
thanks- keep hearing fine to sandwich sheeting with ice/water out and closed cell in, but….
 

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From what I've gathered by reading about this on here and other forums, it has something to do with the amount of r value. Not enough and the temp differential between outside and in gets you condensation. Take this with a grain of salt, I'm not an expert.
 

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From what I've gathered by reading about this on here and other forums, it has something to do with the amount of r value. Not enough and the temp differential between outside and in gets you condensation. Take this with a grain of salt, I'm not an expert.
Got it, thanks
 

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Can't speak to your situation exactly not having seen it firsthand. But in the 30 yrs I've been doing residential re-roofs every single home that had foam (panels or spray) tight to the underside of the roof sheathing had issues with sweating (condensation), form just a bit of dampness to full blown rotted sheathing and rafters. Those homes the had good postive ventilation of the sheathing underside had little or no issues.
Hello-We're in Minneapolis MN and had a 'hot roof' polyfoam install done directly onto deck in the attic & knee walls. No one told us there should be ventilation somewhere. Where would the ventilation have been? We were told no ventilation needed-& to remove the 'bird' vents that are now there-they fill those holes w/ plywood, then roof felt, then shingles w/ ice & water shield around perforationns & up 6' at eaves & valley. But no one talked about ventilatiion for foam job. Help. We need a new roof now & not sure how to deal with roof rot at tear-off time, & how to repair damaged foam if we need to. We'll be using class 4 GAF shingles. Also not sure how to write this into the contract wo we're protected-any thoughts here?
 

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It's to my understanding that when a roof is insulated at the actual roof rafters and not the ceiling joists you have a closed system and do not want ventilation.
 

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It's to my understanding that when a roof is insulated at the actual roof rafters and not the ceiling joists you have a closed system and do not want ventilation.
That's correct per my research, & manufacturers. I wonder about underlayment before tthe singles-maybe a good idea to putt down ice & water shield over the whole roof just to be on the safe side, instead of only 6' up the eaves, & around penetrations; just cover the entire roof, then shingle it?
 
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