Rigid Foam Under Roof Deck

At r 4 it also has the lowest r value per inch.

Rigid foam under roof deck.

After the roof deck is prepared the rigid foam boards need to be cut to size to fit snugly together on your roof. All three types of rigid foam insulation expanded polystyrene eps extruded polystyrene xps and polyisocyanurate are suitable for use on the exterior of walls and roofs though they do not perform equally. Attach to deck board. Install nailbase for cladding.

Nailbase must be vented in high snow load areas. Rigid insulation layers exterior to existing roof sheathing must provide sufficient thermal insulation r value to control condensation risk see climate specific guidance. The purpose of the requirement that rigid foam installed above roof sheathing meet certain minimum r values is to ensure that the roof sheathing stays warm enough during the winter to avoid moisture accumulation and possible sheathing rot. Unvented attics that are insulated on the underside of the roof deck with blown spray foam.

And vented or unvented attics that are insulated above the roof deck with rigid foam. Rigid foam is produced in various size panels 4 ft x 8 ft 4ft x 4ft etc. Install roofing underlayment flashing and cladding as per best practices. Eps is the most vapor permeable of the three types.

High efficiency attic insulation helps provide added thermal protection lessens wasted energy and increases enhanced comfort and quiet.