Air Seal Attic Knee Wall

Insulating air sealing attic knee walls.

Air seal attic knee wall.

There are arguments about shingle life over a hot roof vs vented but shingle color is more significant and as already stated one can install ventilation chutes. Knee walls have r 13 fiberglass rolls also called batts in them covered with stapled on reflective insulation. Despite all the bad publicity reflective insulation is getting lately i like to use it quite a bit on knee walls. Knee walls are among the biggest air leakage and heat loss sources in home in part because they are such a pain in the rear to insulate and air seal properly.

I recently had an energy audit done and the auditor gave me a quote for air sealing the attic sealing top plates and any wire plumbing and lighting penetrations. Cover the insulation with a sheet material drywall or rigid foam insulation that is caulked where it meets the plywood floor sheathing which is extended to the outside wall. Anytime i conduct an energy audit of a cape cod or 3 story colonial or a salt box i know that a good chunk of the homeowner conversation and audit report will deal with the knee walls. An attic access that is perpendicular to the floor.

Installing batt insulation that extends into the attic past the 2 4 studs making sure it doesn t flop over into the attic by adding some kind of bracing and then adding a 2 piece of rigid board insulation on the non attic side of kneewall. Insulation air sealing. This will help reduce the wind damage on the insulation to keep it in. But then for the knee wall it s important to air seal the wall with tyvek or foamboard.

Continue the insulation along the roofline to the roof edge figure 1. Video done by arlington home energy efficiency team during a weatherization barnraising in march 2010. How to air seal a knee wall in a cape. From the inside of the attic a knee wall looks like the image to the left.

The shortest distance from the top of the knee wall to the top of the outside wall beneath is still along the roof line and you avoid having to insulate the floor behind the knee wall. How to air seal knee walls along the roofline. A job we finished last week dropped from 4060 to 2150 cfm50 just with knee wall air sealing we were able to get 8 of one wall that had no top plate. Properly sealing and insulating attic knee walls can significantly reduce air leakage and heat loss between the conditioned space and the unfinished attic.

It is important to choose an air barrier and insulation material that will reduce the air leakage and heat loss as much as possible. I call this tin foil on steroids because that s what it is. Air sealing an attic kneewall the approach used in the video is opposite to what i am thinking of doing. The main purpose of this material is to seal the fiberglass batts.

1000 2000 cfm50 reductions are fairly common with this method. The blue wall in the picture below is the knee wall.