I recently went to visit a spray foam(open cell) install. It did not look to me like the house was ready for foam. There were large gaps between the top of the wall plate and the roof deck without any backer. The installer sprayed to the underside of the roof deck…it expanded…he pulled on it with his glove and then continued to spray.
my question..is there a limit to the size of a gap that can be filled without any backer? The Build America details always show rigid foam or some type of backer.
Replies
Greetings homedesign,
That's a good question.
This post, in response to your question, will bump the thread through the 'recent discussion' listing again which will increase it's viewing.
Perhaps it will catch someone's attention that can help you with advice.
Cheers
"In any weather, at any hour of the day or night, I have been anxious to improve the nick of time, and notch it on my stick too; to stand on the meeting of two eternities, the past and future, which is precisely the present moment; to toe that line."
-Thoreau
My guy won't spray if I don't have all the backing in place.
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Your description is not clear to me. Weren't there rafter blocks or bird blocks? Seems like those would have to be there on top of the wall plates. Maybe the job in question was a hack, where they figure they can save money by skipping the blocking altogether.
Never heard of spray foam used in an attic. This is a little confusing. Cellulose is so inexpensive and the attic large enough to get high R-values w/out the expense of foam. That aside, you need to maintain air circulation from the eave vents to the gable end, rigde vents, or whatever.
Mark Williams, HR,OR
"Never heard of spray foam used in an attic."He did not say that it was used in an attic. He said the bottom of the roof decking. IE, conditioned attic space.and according to his profile he is in texas.Often have HVAC in the attic and with a normal vented attic that can cause lots and lots of loses..
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A-holes. Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.
HVAC in the attic? Then this guy should read the PIER research completed a few years ago related to enclosing attics w/in the heated space. This is a California Energy Commission (CEC) research project that actually took residences built by large builders and tried several strategies to mitigate problems associated w/ HVAC in attics (historically unconditioned).
Still normally would have venting under the roof deck wouldn't we? If so, continuous vent baffles would have to be installed for foam insulation up against it. Am I still missing it? Not sure what was trying to be said about the guy pulling down some of the foam?
Mark Williams HR,OR
"Still normally would have venting under the roof deck wouldn't we?"If it is conditioned space, then NO..
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A-holes. Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.
uhhh, not sure, but even the conditioned attic option vents the roof deck above the conditioned envelope, I would think. While there is such a thing as an unvented roof deck, some jurisdictions may not allow it and some shingle mfg may not allow it, either. Even when you occupy a vaulted attic space, you tend to vent under the roof deck and above the insulation. If it is in fact unvented, then he could fill the area above the plate fully w/ insulation. Put a cardboard baffle in so he doesn't waste money filling up the eaves and he should be good to go.
Mr Energy, here is a link to an example see page 58
http://www.buildingscienceconsulting.com/resources/presentations/Pettit-Integrating_Systems_for_Green_Design.pdf
Some major shingle companies (Elk for one) and jurisdictions allow the practice
The installation I saw did not have any backer or blocking material above the top plate..the installer sprayed foam onto the roof deck..waited for the foam to expand and then took some of that foam and sort-of pulled it into the void with his glove. I agree with piffin I think there should have been backer.
Mr Energy,
Bill H is correct, the home in question will have a conditioned attic or cathedralized ceiling.
<Cellulose is so inexpensive and the attic large enough to get high R-values w/out the expense of foam>
Mark, the advantage of the foam is not the r value it is the superior air sealing.
John