What Is a Knee Wall?

What is a knee wall? These short walls are most commonly found in unfinished attics. While they are not absolutely necessary, they can provide more flexibility in utilizing the attic space. However, knee walls can also pose certain challenges. Let us walk you through everything you should know about knee walls, including their definition, pros, and cons.

What Is a Knee Wall?

Knee walls get their name because they tend to be knee height. Most of them are under three feet tall and are placed under rafters to provide support to your roof. If your attic space doesn’t have knee walls, you can add them to convert the unfinished space into an additional room or build attic closets under a slanted ceiling where it’s too low for you to walk around.

Knee walls can also be used in other slanted spaces. For example, when converting under-the-stairs spaces into nooks, you may need to add a knee wall depending on the space’s size and structure to ensure the stairs can still bear regular foot traffic.

Pros and Cons of Knee Walls

Knee walls are an important part of the roof and provide additional support to your roof and rafters. They are extremely crucial to structural stability in a home with a larger attic or sharper roof pitch. However, knee walls are often overlooked when adding insulation, leaving large air pockets that reduce your home’s energy efficiency. Uninsulated space behind knee walls may be why a finished attic is not comfortable on both hot and cold days.

Knee Wall vs. Pony Wall

Sometimes the terms “knee wall” and “pony wall” are used interchangeably, although they are inherently different. A pony wall is an interior design element often used as a separator in an open floor plan, creating a stronger sense of space and transition. Knee walls are less than three feet tall, but pony walls can sometimes be taller depending on the height of the ceiling. Knee walls are load-bearing, while pony walls are for decorative purposes only.

How to Insulate a Knee Wall

Knee wall insulation is a crucial piece in attic insulation. The best insulation material to use behind a knee wall is insulation batts. They can create a tight seal that prevents outside air from entering. You can then use spray foam insulation to fill in the remaining gaps and spaces.

Be sure to leave a small airway between rafters and the insulation to keep the insulation dry and prevent mold and moisture problems. Also, when adding air barriers between rafters, you should caulk around the barrier for a stronger seal. 

If your attic is already finished, you may need to remove the drywall to reach the space behind the knee walls. Once insulation is complete, you can then reinstall the drywall.