Sprayfoam attic of condo | Ask Mason Knowles - SPF Consultant | Spray Foam Technical Questions and Answers | SprayFoam Magazine Q&A Forums

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Judy Ottley Posted: Jul 14, 2008 06:54 PM	Sprayfoam attic of condo I live in a condo in western Maine. Our Condo board is concerned regarding the breathability if I sprayfoam the eaves and sides making the attic space airtight. One louver vent will need to be sealed. I also have bathroom fans that will need to be vented to the outside. Is there anything I need to know regarding moisture build-up in my condo if I do this? Also how many inches would you recommend for maximum efficiency. The area to cover is approx. 1350 sq ft. Thank you, From Maine
mason Posted: Jul 15, 2008 11:18 AM	Your bathroom vents should already be vented to the outside. If they are vented into your attic, bad things can happen. Way too much moisture that your vented attic cannot handle. Please read my articles on R value and insulation efficiency at masonknowles.com. Check out my blogs as well. You will find that you have to design thickness of SPF based on 3 different factors. 1. Building code requirements 2. Minimum thickness to prevent condensation 3. Maximum insulation efficiency. You will find that ICC building code prescriptive tables will want R 49 in Maine,(way more than what is needed with sprayfoam). The minimum thickness to prevent condensation will be around 2.5 - 3 inches of closed cell foam. The amount needed for maximum insulation efficiency (cost vs effective insulation performance) would be around 4-5 inches of closed cell foam and 8 to 10 inches of low density foam. (Note with the low density foam you will need another vapor retarder element in the design) Hope this helps.
Eric Smith Posted: Oct 07, 2008 11:15 PM	Mason, Where would that Vapor barrier be require to be placed when utilizing an open cell/low density foam. In cold environments, I assume that it would be the last layer prior to sheetrock.
mason Posted: Oct 09, 2008 09:10 PM	Correct, in many cases a coating can be used. Contact the supplier for their recommendations.

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Comments

Judy Ottley

Posted: Jul 14, 2008 06:54 PM

Sprayfoam attic of condo

I live in a condo in western Maine. Our Condo board is concerned regarding the breathability if I sprayfoam the eaves and sides making the attic space airtight. One louver vent will need to be sealed. I also have bathroom fans that will need to be vented to the outside. Is there anything I need to know regarding moisture build-up in my condo if I do this? Also how many inches would you recommend for maximum efficiency. The area to cover is approx. 1350 sq ft.

Thank you,
From Maine

mason

Posted: Jul 15, 2008 11:18 AM

Your bathroom vents should already be vented to the outside. If they are vented into your attic, bad things can happen. Way too much moisture that your vented attic cannot handle.

Please read my articles on R value and insulation efficiency at masonknowles.com. Check out my blogs as well. You will find that you have to design thickness of SPF based on 3 different factors.
1. Building code requirements
2. Minimum thickness to prevent condensation
3. Maximum insulation efficiency.

You will find that ICC building code prescriptive tables will want R 49 in Maine,(way more than what is needed with sprayfoam). The minimum thickness to prevent condensation will be around 2.5 - 3 inches of closed cell foam. The amount needed for maximum insulation efficiency (cost vs effective insulation performance) would be around 4-5 inches of closed cell foam and 8 to 10 inches of low density foam. (Note with the low density foam you will need another vapor retarder element in the design)

Hope this helps.

Eric Smith

Posted: Oct 07, 2008 11:15 PM

Mason,

Where would that Vapor barrier be require to be placed when utilizing an open cell/low density foam. In cold environments, I assume that it would be the last layer prior to sheetrock.

mason

Posted: Oct 09, 2008 09:10 PM

Correct, in many cases a coating can be used. Contact the supplier for their recommendations.

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