Spray Foam Insulation On Roof Deck

Unvented roofs with spray foam applied to the underside of the roof deck have been used since the mid 1990s.

Spray foam insulation on roof deck.

Rigid foam board is just above the roof deck or an exterior insulation option. Both open cell and closed cell spray foam insulation adhears extremely well to the underside of roof decks and the rafters surrounding them when installed correctly. Unlike solid insulation products that require careful measurement cutting and fitting spray foam can cover even the most uneven surface instantly. Polyurethane or polystyrene spray foams can provide thorough coverage to roof rafters and attic walls in much less time than is needed for other materials.

Murmurs and hearsay about open cell spray foam insulation have been gaining traction for a while. The code allows for insulation directly to the underside of the structural roof sheathing providing the unvented attic is contained completely within the. I have not heard of any evidence to support your theory. As air impermeable insulation spray foam insulation can be used in such applications.

In the northwest where foam has been sprayed directly to the underside of roof decks for over a decade the building officials interpret the code to require removal of existing insulation. Spray foam insulation applied on the underside of the roof deck in cold climate commercial buildings allows for a significant reduction in condensation potential particularly compared to interior air permeable batt systems. The previous four options are all used beneath the roof. Bare foam board one sided sheathing board or double sided which is also reference as structural insulated panels.

This should not be a concern when applying foam to the underside of a roof deck. But spray foam insulation used at the underside of the roof deck would need to be covered by a thermal barrier and intumescent coatings are commonly used. This is a great question. The movement of air into indirect conditioning of an unvented attic is a slow gradual process that will not be noticeable by occupants and typically will not put any strain on the hvac system.

Not long ago someone even told me that in florida roofing companies won t let their workers go up on roofs with open cell spray foam because the roofs are so spongy the guys fall right through. 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.