Closed cell foam pulling away from roof sheathing
sean1918
| Posted in General Questions on
Hi, I was curious if anyone has heard of issues of closed cell foam sprayed to the underside of roof sheathing (unvented low slope 1:12 roof) pulling away from the sheatihng over time which would result in moisture issues. I was thinking of doing 4.5″ closed cell and 9″ dense packed cellulose.
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Replies
This can happen in two cases that I'm aware of:
1- Sometimes the cured spray foam shrinks over time and pulls away from the framing. This is pretty rare. In my experience, this usually happens pretty soon after installation, and you can "fix" it by just filling the gap with canned foam.
2- When it's very cold or the wood structure is damp (very high moisture content, or surface wetness), the foam doesn't always adhere well and can seperate or "slump" during installation. This is why it is very important to do the application above freezing, and ideally above about 50*F. You want the structure to be reasonably dry too, and you absolutely do NOT want any surface dampness (i.e. the wood should be dry to the touch). It's also important that the spray foam chemical mix be at the correct temperature, but that's really more the responsibility of the spray foam contractor than the owner or GC at the site.
Bill
Thats good to know regarding the rare issue you have seen and it happening soon after installation. If thats the case then I would be able to see the issues if apparent enough and I appreciate the knowledge of making sure strucuture is dry and not cold (below 50) or damp. I will make sure to delay any insulation till spring/summer/early fall for insulation.