Fine Home Building Insulating Knee Walls Roof

If you are designing or building a new cape you shouldn t have to worry about the air sealing and insu lation problems discussed here as long as you plan from day one to include an insulated sloped roof assembly that brings the attic and kneewall spaces inside the home s thermal barrier.

Fine home building insulating knee walls roof. Few building materials have been embraced by so many builders as rigid foam insulation certainly there are builders who avoid it but rigid foam can be used everywhere from beneath a basement slab to the rooftop and that versatility gets it into a lot of residential projects. Another alternative for knee walls conditions is to remove and reinstall the batt insulation to qii standards. Blown insulation in the knee wall and top attics. There are many ways to build an insulated sloped roof.

In tight attics or odd shaped wall conditions i e. An unvented assembly can perform well but it s important to get the details right to avoid sheathing rot. Added bonus the floor of this knee wall leaked too so there is a line of foam just above the floor joist. We reduced the air leakage nearly 50 on this house in shaker heights without insulating the walls.

We prefer cellulose but we use fiberglass sometimes too. Kneewalls short walls under sloped ceilings are common in story and a half homes and in bonus rooms above garages. There are several common types of rigid foam insulation each with different pros and cons. Air permeable insulation such as fiberglass batts dense packed cellulose or blown in fiberglass can t be used alone for an unvented assembly since these types of insulation can allow moist indoor air to reach the cold roof sheathing leading to condensation or moisture accumulation.

Insulating only the attic roof rafters and the walls at the end of the attic is one method some use to insulate the knee wall area underneath but carson dunlop author of principles of home. Then cover that same area with an r 8 fsk affixing it using cap nails. Thick rigid foam insulation onto the metal ties. Rake walls it s easier to handle than plywood or thermo ply and still gives you an r 19 r121 assembly.

2d extend insulation into joist space to reduce air flows. Insulating the knee wall with rigid foam keeps stone and cement which are poor insulators from conducting cold and dampness into the greenhouse.