Expanding Foam On Roof Deck

Foam sealant won t stick well to a wet surface.

Expanding foam on roof deck.

It is mixed in the bag to produce expanding foam for supporting and backfilling fence mail box gate and signage posts. I just inspected a new home with expanding foam insulation sprayed into the attic along the roof deck. 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. Expanding polyurethane foam sealant requires moisture to expand and cure.

The whole job looked like it was done by cans. Sika postfix is a two component pre proportioned polyurethane resin. 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. This gives a 1 air space between the roof deck and the insulated area.

This section outlines the conditions for unvented attic roof assemblies. It involves adding an air chamber under the roof deck. Eric novotny an informed customer is the best customer. 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.

Rafter tails are exposed no fascia and soffit and the vents originate where the siding meet the roof deck and the vents dump into the short attic space. We then vented that space through the roof deck as was the normal practice for roofing. 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. There were several locations where i could see gaps.

The last i saw a video on this type of insulation it was sprayed with a special wand that filled the cavity between studs and then they scraped off the excess along the face of the studs. 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. You want to dampen the area not wet it. The damp foam can then transfer the moisture to rafters and decking materials leading to rot or leakage.

On one project in kansas we installed 1 x 1 along both sides of the rafters and then added 3 8 plywood to them. 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. The ridge would be vented. 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.