We are finishing an attic in Atlanta GA and are looking at sprayed polyeurathane foam for the sloped ceiling, gables, and kneewalls. However, we have several unanswered questions.
Contractors would spray the foam directly on the underside of the roof deck. Should we be concerned about the roof heating (shingle damage) with no ventilation under the deck?
Contractors tell us about 3″ on the roof deck and 2″ on the vertical walls is more than adequate because of added reduction in air movement. Should we consider adding more insulation (fiber glass or cellulose) below the foam? We have a total of 8″ from roof deck to sheetrock ceiling.
We were going to use foil backed polyiso board on the backs of the kneewalls to spray the foam on. The area behind the kneewalls (actually a bit over 4′ high) will be used for storage and HVAC. Do we need to be concerned about a thermal barrier on the unconditioned side of the wall if we use the polyiso board?
This type of foam used to be known as using ozone depleting chemicals to install it. Today is an ozone alert here in Atlanta. Does anyone know if the latest generation of these spray foams still carries this concern?
Comments on these questions and any other thoughts on spray polyeurathane are welcomed.
dan
Edited 6/12/2002 8:54:11 AM ET by danlmac
Replies
Why are you not spraying all the way to the eaves? Your HVAC ducts will be more efficient if they are inside the conditioned space rather than behind the insulated knee wall. Spray first, then wall it off with drywall rather than the polyiso.
No ozone hole eaters allowed anymore, and the ozone alert is because there's too much ozone. Go figger. Joe H
Joe:
Thanks for the response.
We are spraying down to the eaves on the side where the kneewalls are short. On the high side there is a large unconditioned area and spraying all the roof is well beyond our budget. The HVAC ducts are insulated but I am considering spraying the foam over them (or wrapping with cheaper fiber glass).
Yeah the ozone puzzles me too. Glad to know the foam has resolved that problem.
dan
Ozone is hard on biological systems. That's why ozone water purifiers work and why it makes eyes and lungs burn. It also absorbs UV light. So ozone at ground level is bad, ozone in the stratosphere is good.