5" open cell in north | Ask Mason Knowles - SPF Consultant | Spray Foam Technical Questions and Answers | SprayFoam Magazine Q&A Forums

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Matt Kenner Posted: Sep 17, 2009 11:09 AM	5" open cell in north When applying 5" of open cell in northern states (zone 5 or higher), should poly or some other vapor retarder be applied in the wall cavity along with the spray foam before putting up drywall?
mason Posted: Sep 17, 2009 11:48 AM	The vapor retarder would go on top of the foam after installation not on the substrate before installation in northern climates.
Matt Kenner Posted: Sep 18, 2009 02:13 PM	Is the poly necessary (is it standard practice)? If it is, would applying closed cell be a better idea (vapor barrier built in), thereby eliminating the need for poly?
mason Posted: Sep 18, 2009 02:30 PM	You don't have to use poly, there are some other options. such as coatings, Check with the supplier for their recommendations
jimcoler I have over 10 years of experience specifying and installing open and closed cell spray foam. I've sold my business but I'm still selling for the new owners and consulting on large and custom specific jobs. I've expanded my knowledge into t Posted: Sep 21, 2009 05:53 PM	I would not recommend using poly on any insulation - Just as Joe Lstibruk of Building Science.com doesn't recommend it. Poly as a vapor barrier has the potential to prevent moisture that gets in from getting out and drying to the inside. The IRC 2006 codes have gotten away from the term of vapor barrier al together and replaced it with class I, II,& III vapor retarders depending on the climate zone you're applying it. Depending on the type of foam you're using and the perm rating at the desired thickness, some .5lb foams don't require a moisture retarder as they are a class III vapor retarder. Check with your foam supplier for these details. Jim Coler

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Comments

Matt Kenner

Posted: Sep 17, 2009 11:09 AM

5" open cell in north

When applying 5" of open cell in northern states (zone 5 or higher), should poly or some other vapor retarder be applied in the wall cavity along with the spray foam before putting up drywall?

mason

Posted: Sep 17, 2009 11:48 AM

The vapor retarder would go on top of the foam after installation not on the substrate before installation in northern climates.

Matt Kenner

Posted: Sep 18, 2009 02:13 PM

Is the poly necessary (is it standard practice)? If it is, would applying closed cell be a better idea (vapor barrier built in), thereby eliminating the need for poly?

mason

Posted: Sep 18, 2009 02:30 PM

You don't have to use poly, there are some other options. such as coatings, Check with the supplier for their recommendations

jimcoler

I have over 10 years of experience specifying and installing open and closed cell spray foam. I've sold my business but I'm still selling for the new owners and consulting on large and custom specific jobs.

I've expanded my knowledge into t

Posted: Sep 21, 2009 05:53 PM

I would not recommend using poly on any insulation - Just as Joe Lstibruk of Building Science.com doesn't recommend it. Poly as a vapor barrier has the potential to prevent moisture that gets in from getting out and drying to the inside. The IRC 2006 codes have gotten away from the term of vapor barrier al together and replaced it with class I, II,& III vapor retarders depending on the climate zone you're applying it.

Depending on the type of foam you're using and the perm rating at the desired thickness, some .5lb foams don't require a moisture retarder as they are a class III vapor retarder.
Check with your foam supplier for these details.
Jim Coler

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