Rigid Foam Attic Knee Wall

A knee wall is a short vertical wall roughly two or three feet high that blocks in that useless triangular space.

Rigid foam attic knee wall. Blown insulation in the knee wall and top attics. This method of insulation won t work if the triangular attic includes ducts or plumbing pipes. Here are the three keys to sheathing an attic kneewall properly. First you will want to add traditional insulation between the studs this can be batt insulation spray foam or even rigid foam insulation.

Both can be done poorly of course and i ve seen both done poorly. I d prefer to see a rigid material on attic kneewalls. Rigid foam insulation is the solution. The disadvantage is that it would be very very hard to reach the desired r value from r 49 to r 60 depending on climate for attic insulation.

How to insulate knee walls. An insulated kneewall is effectively an exterior wall so you ll need a layer of rigid foam drywall osb or thermoply on the back side of the kneewall to prevent cold air from degrading the performance of the insulation. I think the rigid material will do a better job with air sealing and will stay intact longer. Install a continuous air barrier on the exterior side of the attic knee wall framing with a rigid air barrier or other supporting material to prevent the knee wall cavity insulation from sagging and to create a continuous thermal barrier.

Rigid air barrier material could include rigid foam insulation drywall plywood or osb among others. The higher the knee wall the greater the amount of useful wall space you create in your finished attic. Rigid foam insulation is innovative eye pleasing and super effective. The advantage here is that your knee wall is probably already insulated this way so it s just a matter of buying some foam so cheap.

It easily expands with graphite infused right into the foam while we air seal the edges to provide the full maximum insulation. Knee walls that share space with a conditioned room in your home should have a combination of both traditional insulation and foil radiant barrier insulation. We prefer cellulose but we use fiberglass sometimes too. Wondering how you can make your knee wall space insulated correctly.

In this case after insulating the stud cavities with fiberglass batts use 1 inch minimum rigid foam insulation to cover the back of the knee wall which will prevent attic air from circulating around and through the insulation. Cover the whole wall. Added bonus the floor of this knee wall leaked too so there is a line of foam just above the floor joist.