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MHMHM Posted: Oct 24, 2016 02:08 AM	Spray foam thickness variation I've got a new construction house in upstate NY with a vented crawl space. It's supposed to have R30 open cell spray foam insulation in the 1st floor floor joists. Upon inspection I noticed that there were a few areas where it was slightly over the 8.33" required to achieve R30 and a lot of areas where it's significantly below. Like 2 to 4" in many places and probably like 5" or more in some places. The GC had the foam installer come back. At first the foam installer tried to argue that it's the average that counts but then agreed to come back and apply more. They came back with a closed cell kit and filled in some of the low spots but still left a lot of low spots. What amount of variation below the minimum thickness is acceptable? I'm willing to accept some variation but many large spots 25 to 50% below seems like too much. Thanks
mason Posted: Oct 24, 2016 12:24 PM	SPFA's Consultant Committee addressed the topic in an article that is too long for this forum. Email me masonknowles@aol.com to obtain a copy. This is a common dispute that is hard to resolve after the application. Ideally, how to measure the foam should be addressed before the application. The contractor should have in their proposal how the foam will be measured. Just saying a specific thickness doesn't provide a guideline on how to measure the foam. The best specifications have an average thickness with a minimum and a maximum tolerance, plus the size of area that would constitute a defect. For example a 1 inch square of low thickness would not normally be considered a defect unless it would create a condensation issue. My opinion is that an average of 8.3 inches of open cell SPF would be sufficient to provide a R value of 30. However, I would not expect more than a 4 inch variance in thickness. If there are areas where the foam is 6 inches and other areas equal in size and number that are 10 inches then you should have the same performance and I would accept the application. But, if there are areas with less than 6 inches of foam than I would recommend more foam be added. Another thing to consider is how much foam is needed to minimize the potential for condensation. Crawl spaces are typically high humidity areas and open cell foam has a higher permeance than closed cell foam. You require a minimum thickness to control condensation on the underside of the first floor. Check out SPFA's Moisture Transmission Paper at sprayfoam.org to calculate the thickness needed. Also, In your region you require a vapor retarder coating over the open cell foam to minimize the water vapor drive into the foam. Make sure the contractor has this included in his bid.

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MHMHM

Posted: Oct 24, 2016 02:08 AM

Spray foam thickness variation

I've got a new construction house in upstate NY with a vented crawl space. It's supposed to have R30 open cell spray foam insulation in the 1st floor floor joists. Upon inspection I noticed that there were a few areas where it was slightly over the 8.33" required to achieve R30 and a lot of areas where it's significantly below. Like 2 to 4" in many places and probably like 5" or more in some places. The GC had the foam installer come back. At first the foam installer tried to argue that it's the average that counts but then agreed to come back and apply more. They came back with a closed cell kit and filled in some of the low spots but still left a lot of low spots.
What amount of variation below the minimum thickness is acceptable? I'm willing to accept some variation but many large spots 25 to 50% below seems like too much.
Thanks

mason

Posted: Oct 24, 2016 12:24 PM

SPFA's Consultant Committee addressed the topic in an article that is too long for this forum.
Email me masonknowles@aol.com to obtain a copy.

This is a common dispute that is hard to resolve after the application. Ideally, how to measure the foam should be addressed before the application. The contractor should have in their proposal how the foam will be measured.

Just saying a specific thickness doesn't provide a guideline on how to measure the foam. The best specifications have an average thickness with a minimum and a maximum tolerance, plus the size of area that would constitute a defect. For example a 1 inch square of low thickness would not normally be considered a defect unless it would create a condensation issue.

My opinion is that an average of 8.3 inches of open cell SPF would be sufficient to provide a R value of 30. However, I would not expect more than a 4 inch variance in thickness. If there are areas where the foam is 6 inches and other areas equal in size and number that are 10 inches then you should have the same performance and I would accept the application. But, if there are areas with less than 6 inches of foam than I would recommend more foam be added.

Another thing to consider is how much foam is needed to minimize the potential for condensation. Crawl spaces are typically high humidity areas and open cell foam has a higher permeance than closed cell foam. You require a minimum thickness to control condensation on the underside of the first floor. Check out SPFA's Moisture Transmission Paper at sprayfoam.org to calculate the thickness needed.

Also, In your region you require a vapor retarder coating over the open cell foam to minimize the water vapor drive into the foam. Make sure the contractor has this included in his bid.

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