knee wall insulation and air sealing
Knee walls – often found in houses with finished attics – are vertical walls with attic space directly behind them. These walls are notoriously leaky and often uninsulated. For energy efficiency, a knee wall and the attic floor in the attic space behind it should be properly insulated and air sealed.
Insulation and air sealing techniques
When installing the insulation, you can use twine to hold batt insulation in place. The technique of adding rigid foam insulation over the framing is particularly effective. Rigid insulation can be notched to fit over the floor joists. Sealing rigid insulation to floor joists effectively blocks open floor joists.
The best approach for creating an energy-efficient knee wall is to insulate and air seal the rafter space along the sloping ceiling of the knee wall attic space:
One advantage of this approach is that any ductwork located in this space is now inside the conditioned space. Therefore, the ductwork won't require insulation.
Another approach includes the following steps:
Whatever approach you use, you'll also want to properly insulate and air seal the knee wall door.