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stan greenwood Posted: May 16, 2009 02:17 PM	Shingling, cathedral ceiling, spray foam and venting. I can't seem to get the same answer out of two peeps on this question. I want to reshingle my old roof which will turn out to be a cathedral ceiling. I'm worried about the shingles being able to breath after I spray foam between the rafters and want to know the right method to proceed with venting, or if I need to vent at all if I can provide an air tight situation. I plan to use 2 lb closed cell foam and the roof sheathing is actually 1" boards, the shingles will be a 30 - 40 year asphalt shingle product. The actual rafters are also rough 2x4's so I should get 4"s of foam up there. The only thing I need to extend through the roof will be an abs plumbing stack. I'm also worried about the spacing that is present between these boards and if I need to be concerned with foam pushing up the shingles. This house is in Toronto, where we can suffer severe snow in the winter and blistering heat in the summer.
mason Posted: May 16, 2009 04:40 PM	Venting the cathedral ceiling or attic space reduces the benefits of the sprayfoam. Research and field history has demonstrated that installing foam to the underside of the roof deck does not add significantly to the temperature of the shingles or lead to premature deterioration. However, a few shingle manufacturers have warranties that do not allow unvented attics and foam installed to the underside of the roof deck without ventilation. Find a shingle manufacturer (such as GAF/ELK or Certainteed) that allows the use of this very beneficial approach to insulating attics and cathedral ceilings.
stan greenwood Posted: May 16, 2009 06:10 PM	Hi Mason, thank you for the reply, the only other thing that might concern me now is whether the foam, may push up the shingles from between the boards. If this could be a problem might their be a simple fix without sheathing the whole roof with plywood.
Roger Morrison Posted: May 17, 2009 02:50 PM	You are correct to be concerned. SPF can expand out crevasses and warp the shingles. Forget about any shingle warranty if this happens. How much space is between the boards?
Posted: May 19, 2009 06:34 AM	i have done this application in the past,,with no untoward results,,,i would prefer not to do this app this way,,and i inform the customer that it is a compromised app...informed decisions rule!! obviously the foam will bond with whatever is bridging the gaps in the planking,,roof felt,,shingles,,,whatever,,,i have not seen it warp shingles with even as much as a 1" gap... foam will follow the "path of least resistance" in its rise,,,and if you spray the way you should,,an 1" pass or so your chance of pushing these shingles up are reduced,,,if you spray directly to them you are hosed on your warranty,,,no doubt about it,,,life is full of choices,,,some right,,some wrong,,but this is an existing old shingle roof so there is no warranty to worry about here,,and you mention you plan to re-shingle the roof,,,why not strip and sheet it and shingle and then foam,,as it should be done??? or,,, put a piece of tape across the gap and spray away if your freaked out about spraying into the gap..or stuff em with filerglass,,,makes a great block out,,,or this could be a perfect application for a froth pak,, like they try to sell for sidewalls,,you know the swelling foam that adds r value but does little to expand into the cracks and creaveses to create a true air barrier,,,caulk the gaps,,,neccessity is the mother of invention,,, hope this helps,, 'dude
stan greenwood Posted: May 19, 2009 09:19 AM	Gentlemen, big thank you for your comments, I definitely learned what I need to know to go ahead and get this job done properly!!!

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Comments

stan greenwood

Posted: May 16, 2009 02:17 PM

Shingling, cathedral ceiling, spray foam and venting.

I can't seem to get the same answer out of two peeps on this question. I want to reshingle my old roof which will turn out to be a cathedral ceiling. I'm worried about the shingles being able to breath after I spray foam between the rafters and want to know the right method to proceed with venting, or if I need to vent at all if I can provide an air tight situation. I plan to use 2 lb closed cell foam and the roof sheathing is actually 1" boards, the shingles will be a 30 - 40 year asphalt shingle product. The actual rafters are also rough 2x4's so I should get 4"s of foam up there. The only thing I need to extend through the roof will be an abs plumbing stack. I'm also worried about the spacing that is present between these boards and if I need to be concerned with foam pushing up the shingles. This house is in Toronto, where we can suffer severe snow in the winter and blistering heat in the summer.

mason

Posted: May 16, 2009 04:40 PM

Venting the cathedral ceiling or attic space reduces the benefits of the sprayfoam. Research and field history has demonstrated that installing foam to the underside of the roof deck does not add significantly to the temperature of the shingles or lead to premature deterioration. However, a few shingle manufacturers have warranties that do not allow unvented attics and foam installed to the underside of the roof deck without ventilation.

Find a shingle manufacturer (such as GAF/ELK or Certainteed) that allows the use of this very beneficial approach to insulating attics and cathedral ceilings.

stan greenwood

Posted: May 16, 2009 06:10 PM

Hi Mason, thank you for the reply, the only other thing that might concern me now is whether the foam, may push up the shingles from between the boards. If this could be a problem might their be a simple fix without sheathing the whole roof with plywood.

Roger Morrison

Posted: May 17, 2009 02:50 PM

You are correct to be concerned. SPF can expand out crevasses and warp the shingles. Forget about any shingle warranty if this happens. How much space is between the boards?

Posted: May 19, 2009 06:34 AM

i have done this application in the past,,with no untoward results,,,i would prefer not to do this app this way,,and i inform the customer that it is a compromised app...informed decisions rule!!
obviously the foam will bond with whatever is bridging the gaps in the planking,,roof felt,,shingles,,,whatever,,,i have not seen it warp shingles with even as much as a 1" gap...
foam will follow the "path of least resistance" in its rise,,,and if you spray the way you should,,an 1" pass or so your chance of pushing these shingles up are reduced,,,if you spray directly to them you are hosed on your warranty,,,no doubt about it,,,life is full of choices,,,some right,,some wrong,,but this is an existing old shingle roof so there is no warranty to worry about here,,and
you mention you plan to re-shingle the roof,,,why not strip and sheet it and shingle and then foam,,as it should be done??? or,,,
put a piece of tape across the gap and spray away if your freaked out about spraying into the gap..or stuff em with filerglass,,,makes a great block out,,,or this could be a perfect application for a froth pak,, like they try to sell for sidewalls,,you know the swelling foam that adds r value but does little to expand into the cracks and creaveses to create a true air barrier,,,caulk the gaps,,,neccessity is the mother of invention,,,
hope this helps,,
'dude

stan greenwood

Posted: May 19, 2009 09:19 AM

Gentlemen, big thank you for your comments, I definitely learned what I need to know to go ahead and get this job done properly!!!

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