My aunt just had a house built in northern MN with full spray foam. 2x6 walls filled with foam, hot roof with no rigid foam like you described. The HVAC contractor forgot to turn on the air exchanger when they left so the interior humidity was about 50% in Jan when I visited. Really hoping she is able to avoid the cracking and off-gassing problems described here. I'm building my own high efficiency house with zero spray foam.

Very Interesting

If we know spray foam offgasses harmful, odorless chemicals long after installation, what situations would you ever want to use it?

@ASIRIDesigns

5 ай бұрын

Encapsulated underneath a slab or installed on the exterior of a low-sloped roof assembly in a complex re-roofing application are both examples where spray foam can make sense, essentially disconnected from the conditioned space.

@TommyShlong

5 ай бұрын

@@ASIRIDesigns And yet most applications are within the conditioned space. Not good for inhabitants. Are there any types/brands of closed cell foam that aren't toxic and perform as well as the toxic ones?

If the construction has already been done (14 year old build) a vapor barrier would be difficult to put in. In this case, would spray foam be the only other option to deal with condensation?

Is there any concern with sandwiching that OSB roof sheathing between the interior conditioned space spray foam and outboard insulation without an air gap?

@jmo7407

4 ай бұрын

This is what I was wondering. Just run a two inch gap all the way up from the rafters to the ridge so the roof layer is still unconditioned and you have your foam and ridged insulation below that. with 2x8 or 2x10 rafters you have plenty of room although you still get thermal bridging on the actual roof supporting members. A final layer of ridged foam before wallboard to break that gap might be sufficient.