My wife and I are planning an addition to our ranch adding a second
floor and garage. The majority of the ceilings are
designed to be cathedral ceilings. We plan to use a spray foam product
in the ceilings. We have found a lot of conflicting information on
whether or not to ventilate the ceiling. Can someone provide the most up to
date “best practice” for this situation?
Replies
My wife and I are planning an addition to our ranch adding a second
floor and garage. The majority of the ceilings are
designed to be cathedral ceilings. We plan to use a spray foam product
in the ceilings. We have found a lot of conflicting information on
whether or not to ventilate the ceiling. Can someone provide the most up to
date "best practice" for this situation?
This is better
Life is not a journey to the grave with the intention of arriving safely in a pretty and well preserved body, but rather to skid in broadside, thoroughly used up, totally worn out, and loudly proclaiming
WOW!!! What a Ride!
Forget the primal scream, just ROAR!!!
No vents, spray the foam.
Joe H
That depends a bit on where you are. I favor unvented roofs, but would avoid open cell foam, such as icynene, in areas where there's a strong winter vapor drive. That means, if it gets cold where you are, use closed cell foam.
If you're in a cooling climate - say, Texas, it might behoove you to sheathe the roof with a low-e plywood such as LP's TechShield. That stuff is said to re-emit only 5% of the heat from the roof above, but it needs an airspace below or the heat simply transfers through conduction. (Note - TechShield is not a radiant reflector, but a low emissivity sheathing - Don't confuse it with the radiant barrier films whose performance is sketchy). I'd still foam the cavities there, and would be comfortable with open cell foam, but would be sure to create 1 in. airspace between it and the sheathing (not for ventilation, just to enable the low-e sheathing).
And, if you're in a heating climate, look at GAF's 3M heat reflective shingles.
Andy
"Never try to teach a pig to sing. It wastes your time and annoys the pig." Robert A. Heinlein
"Get off your dead #### and on your dying feet." Mom
AndyI only use Icynene in such ceilings up here. (Western MA) .. but I am wondering if there is easy way to explain the difference between this 'open cell'spray foam insulation versus the 'closed cell and what is a common brandname around here for the 'closed cell' spray foam insulation. thanksArthurhttp://www.thesmallbuildingcompany.com
Interesting. Icynene does not, as I understand it, comply with the CT code for use in unvented roofs. It's an open cell foam, and the CT code allows only closed cell.
Don't have other brand names, but polyurethane foams are generally closed cell.Andy
"Never try to teach a pig to sing. It wastes your time and annoys the pig." Robert A. Heinlein
"Get off your dead #### and on your dying feet." Mom