How Do You Insulate Knee Walls In An Attic

The traditional approach is to insulate the kneewall and the attic floor behind the kneewall.

How do you insulate knee walls in an attic.

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. If your attic has knee walls install insulation only in the rafters above the knee wall. A better approach is to insulate the roof slope above the attic. If you go back and view the illustration above you ll notice there s an enclosed area behind the knee wall.

In this case the area behind the knee wall will be uncomfortably hot or cold. The higher the knee wall the greater the amount of useful wall space you create in your finished attic. Rake walls it s easier to handle than plywood or thermo ply and still gives you an r 19 r121 assembly depending on the original batt insulation installed. If only the living space will be insulated wrap the insulation around the room s walls and ceiling and then continue along the floor of the non living space.

A knee wall is a short vertical wall roughly two or three feet high that blocks in that useless triangular space. But you do so at the expense of floor space. There are two basic ways to insulate a finished attic. The ceiling and knee wall drywall will act as your air barrier.

In finished attic rooms with or without dormer insulate 2a between the studs of knee walls 2b between the studs and rafters of exterior walls and roof 2c and ceilings with cold spaces above. A house wrap like tyvek or a perforated with pinprick holes radiant barrier are good covers for fiberglass in knee walls. If you choose to insulate along the horizontal and vertical walls you have four key air sealing points. Behind the knee wall install batts between the ceiling joists taking care not to block soffit vents and.

There are two ways to insulate triangular attics behind kneewalls. Assuming styrofoam vent chutes are installed rough cut a foam block to fit between the rafters. 2d extend insulation into joist space to reduce air flows. Don t use the usual radiant barriers sold at home depot and lowe s they are not perforated.

Then cover that same area with an r 8 fsk affixing it using cap nails. This method can be made to work but the necessary air sealing details are demanding and fussy. Another alternative for knee walls conditions is to remove and reinstall the batt insulation to qii standards. Knee walls also provide pockets for additional insulation in the attic.

The first point is sealing the soffit venting.