Spray Foam Roof over OSB SIP | Ask Mason Knowles - SPF Consultant | Spray Foam Technical Questions and Answers | SprayFoam Magazine Q&A Forums

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Posted: Nov 11, 2008 04:35 PM	Spray Foam Roof over OSB SIP Could you explain the installation process of a spray foam roof over a low pitch OSB SIP roof. Do you lay down a second layer of OSB and start from there or do you install directly on the SIP? Any other things to keep in mind?
mason Posted: Nov 12, 2008 07:39 AM	You should be able to go over the SIP panel. I would use a primer to enhance adhesion and minimize water absorption in the OSB. My only hesitation would be if there was significant movement of the SIPS panels. If you observe a lot of movement an overlay may be advisable. As always ask you supplier for their written recommendation.
Posted: Nov 13, 2008 07:36 PM	When the time comes to replace a Spray Foam Roof, is there any risk of damaging the layer of OSB that the roof is sprayed onto? In a SIP application this OSB is structural and cannot be replaced. It might be great if you guys contacted the leading SIP manufacturers such as R-Control and put out a white paper on low pitch Spray Foam Roofs over OSB SIPs. I think the two technologies are a good fit. My Gut feeling is that in a SIP application I would lean towards 1" furring strips with a second layer of OSB, with the Spray Foam roof applied on top of that. It may add around $1 a square foot for the OSB and the furring strips, but would provide a breathing space and protect the structural SIP.
mason Posted: Nov 15, 2008 09:17 AM	June, You are thinking too much on this item. The construction you suggest adds cost and complexity to a very simple design. Whenever possible, spray the foam directrly to the decking or at least to a cover board that is securely attached to the decking. Remember most leaks on a SPF roof come from improper edge flashing and through roof penetrations that have become cracked or improperly flashed. The design you propose would be more difficult to find a leak and more expense to fix. Plus, the air gap would be more likely to have a ccndensation point rather than less likely. (again around the through roof vent pipes)
mason Posted: Nov 15, 2008 09:24 AM	By the way, properly installed and maintained, you should not have to replace the foam roof. It needs to be recoated typically every 10 to 15 years depending on the type of coating and the environment.

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Posted: Nov 11, 2008 04:35 PM

Spray Foam Roof over OSB SIP

Could you explain the installation process of a spray foam roof over a low pitch OSB SIP roof.

Do you lay down a second layer of OSB and start from there or do you install directly on the SIP?

Any other things to keep in mind?

mason

Posted: Nov 12, 2008 07:39 AM

You should be able to go over the SIP panel. I would use a primer to enhance adhesion and minimize water absorption in the OSB.

My only hesitation would be if there was significant movement of the SIPS panels. If you observe a lot of movement an overlay may be advisable.
As always ask you supplier for their written recommendation.

Posted: Nov 13, 2008 07:36 PM

When the time comes to replace a Spray Foam Roof, is there any risk of damaging the layer of OSB that the roof is sprayed onto? In a SIP application this OSB is structural and cannot be replaced.

It might be great if you guys contacted the leading SIP manufacturers such as R-Control and put out a white paper on low pitch Spray Foam Roofs over OSB SIPs. I think the two technologies are a good fit.

My Gut feeling is that in a SIP application I would lean towards 1" furring strips with a second layer of OSB, with the Spray Foam roof applied on top of that. It may add around $1 a square foot for the OSB and the furring strips, but would provide a breathing space and protect the structural SIP.

mason

Posted: Nov 15, 2008 09:17 AM

June,

You are thinking too much on this item. The construction you suggest adds cost and complexity to a very simple design. Whenever possible, spray the foam directrly to the decking or at least to a cover board that is securely attached to the decking. Remember most leaks on a SPF roof come from improper edge flashing and through roof penetrations that have become cracked or improperly flashed. The design you propose would be more difficult to find a leak and more expense to fix. Plus, the air gap would be more likely to have a ccndensation point rather than less likely. (again around the through roof vent pipes)

mason

Posted: Nov 15, 2008 09:24 AM

By the way, properly installed and maintained, you should not have to replace the foam roof. It needs to be recoated typically every 10 to 15 years depending on the type of coating and the environment.

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