How Do You Insulate Knee Walls In An 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.

How do you insulate knee walls in an attic.

A knee wall is a short vertical wall roughly two or three feet high that blocks in that useless triangular space. If you choose to insulate along the horizontal and vertical walls you have four key air sealing points. Another alternative for knee walls conditions is to remove and reinstall the batt insulation to qii standards. A house wrap like tyvek or a perforated with pinprick holes radiant barrier are good covers for fiberglass in knee walls.

There are two ways to insulate triangular attics behind kneewalls. Don t use the usual radiant barriers sold at home depot and lowe s they are not perforated. The key is whatever material you use must allow water vapor through it. A better approach is to insulate the roof slope above the attic.

Knee walls also provide pockets for additional insulation in the attic. 2d extend insulation into joist space to reduce air flows. Assuming styrofoam vent chutes are installed rough cut a foam block to fit between the rafters. In tight attics or odd shaped wall conditions i e.

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. The traditional approach is to insulate the kneewall and the attic floor behind the kneewall. Rather than leaving this space empty homeowners can fill it with insulation for additional thermal protection. 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.

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. The first point is sealing the soffit venting. In this case the area behind the knee wall will be uncomfortably hot or cold.

But you do so at the expense of floor space. The higher the knee wall the greater the amount of useful wall space you create in your finished attic. Then cover that same area with an r 8 fsk affixing it using cap nails. If your attic has knee walls install insulation only in the rafters above the knee wall.

This method can be made to work but the necessary air sealing details are demanding and fussy.