Expanding Foam On Roof Deck

The ridge would be vented.

Expanding foam on roof deck.

Spray foam really is a magical tool for household insulation. Expanding polyurethane foam sealant requires moisture to expand and cure. If you use open cell spray foam on your roof rafters you should cover the finished application with a paint or sealant that retards water vapor. Note that table r806 4 indicates the amount of insulation above the roof deck or air impermeable insulation below the roof deck required for condensation control assuming minimum required total insulation as indicated in section n1102 building thermal envelope.

This gives a 1 air space between the roof deck and the insulated area. Foam sealant won t stick well to a wet surface. The whole job looked like it was done by cans. On one project in kansas we installed 1 x 1 along both sides of the rafters and then added 3 8 plywood to them.

We then vented that space through the roof deck as was the normal practice for roofing. My plan had been to install site built baffles in order to provide a 2 airspace between the foam and underside of the roof deck. Sika postfix is a two component pre proportioned polyurethane resin. Sloped roof with cavity spray foam insulation sprayed on underside of roof deck and covered with a sprayed on thermal or ignition barrier coating over the spray polyurethane foam insulation if necessary based on the material properties of the spray polyurethane foam or as required by code source.

I just inspected a new home with expanding foam insulation sprayed into the attic along the roof deck. Suitable for all types of posts including wood steel and pvc. The damp foam can then transfer the moisture to rafters and decking materials leading to rot or leakage. There were several locations where i could see gaps.

Eric novotny an informed customer is the best customer. This section outlines the conditions for unvented attic roof assemblies. It involves adding an air chamber under the roof deck. Although fiberglass has been commonly use for insulation spray foam can actually outperform it plus with so many ways you can use expanding foam this material certainly is handy now only if it could help us out with all of those concrete problems.

If you re applying foam to dry wood or other dry surfaces or working on a day with little humidity misting the area first will help the foam expand and cure faster. I would apply sufficient rigid foam to the outside of the roof deck and create an insulated roof deck with a combination of rigid foam and some above deck venting. You want to dampen the area not wet it. That would be the best of both worlds.