Rigid Foam Under Roof Deck

Where rigid insulation is installed above the roof deck or air impermeable spray foam insulation is installed under the roof deck condensing surface temperatures are said to be controlled.

Rigid foam under roof deck.

At r 4 it also has the lowest r value per inch. If you want to install rigid foam above your roof sheathing in climate zone 3 then 1 2 inch of rigid foam board is not ideal this rigid foam layer needs a minimum r value of r 5 and that s impossible with 1 2 inch of foam. Rigid insulation layers exterior to existing roof sheathing must provide sufficient thermal insulation r value to control condensation risk see climate specific guidance. That way you get an air space and an additional r 2 or r 3 for the assembly not a lot but something.

Nailbase must be vented in high snow load areas. Install roofing underlayment flashing and cladding as per best practices. Moisture generated indoors or that infiltrates into the home is responsible for the bulk of the moisture in an attic insulated with spray foam on the underside of the roof sheathing. They had to look original.

Eps is the most vapor permeable of the three types. When installing a foil faced foam board insulation. The 6 inches of rigid insulation added to the top of the existing roof deck needed to be done in a manner that was invisible. Install nailbase for cladding.

The trim the frieze boards the fascia and the overhangs all had to look like they belonged. In addition to installing the foam board on the underside of the roof deck you can attach it to the bottom edges of the. 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. Lstiburek takes blame for bad language.

Most unvented attics incorporate spray polyurethane foam spf on the underside of the roof deck and attic walls. When installing rigid insulation in an attic to be finished as a living space you must provide a route by which hot air. No air space no benefit. Rigid foam under roof sheathing alaskan andy is right.