Expert: Ted Barnhill (Principal, Design45 LLC) - 5/10/2011

Question
Hi Ted,
I have a house built in 1978 with a 1.25 in 12 pitch roof with soffit venting at the peak. The joists are 2x10" with 6 inches of fiberglass insulation leaving an air channel above the insulation for the venting. If I replace the fiberglass with urethane foam insulation would I still need the vent channel.

Thanks in advance.

Walt Ford

Answer
Walt,

According to current code, you can remove the venting and go to what is known as a "hot" roof, if your foam is installed in a certain way.  Whether this is the best solution for you, long term, depends on several factors.  For complicate roof forms, a hot roof can be a great solution.  Personally, for roofs where venting exists or can be properly installed, I am a proponent of closed cell foam with venting.

You might want to look at adding vent "chutes" that will be 1" or so thick, rather than 3"+ of air.  This should provide you adequate venting and give you something to spray foam against (and leave 8" or so for foam, which is more than enough).

Ted Barnhill
Design 45 LLC