How to Build a Knee Wall in an Attic

By
Lee Wallender
Lee Wallender
Lee Wallender

Lee has over two decades of hands-on experience remodeling, fixing, and improving homes, and has been providing home improvement advice for over 13 years.

Learn more about The Spruce's Editorial Process
Updated on 11/28/22
Reviewed by
Kelly Bacon
Kelly Bacon
Reviewed by Kelly Bacon

Kelly Bacon is a licensed general contractor with over 40 years of experience in construction, home building and remodeling, and commercial building. He is a member of The Spruce Home Improvement Review Board.

Learn more about The Spruce's Review Board
View of A-frame attic in a newly-built home
northlightimages / Getty Images
Project Overview
  • Working Time: 2 - 3 hrs
  • Yield: 8-foot knee wall in attic
  • Skill Level: Intermediate
  • Estimated Cost: $50 to $100

Most homeowners want more space. People and possessions have a unique ability to quickly up a vacuum, so space is always at a premium. But it can be hard to find unused space. One typically unused area is the attic.

The attic comes with its own set of challenges: lack of easy access, obstructions, roof insulation. One challenge has to do with the triangular configuration of the attic. The triangular ceiling is usually left as-is, but what about those triangular portions off to the side? The angles are too acute to be functional.

Building a knee wall helps to enclose those acute triangular portions of your attic where the rafters meet the top plate of the wall. Doing this is just one step in finishing off an attic to make it a fully liveable space, and it helps to insulate your attic space against air infiltration from the outside. Use these instructions to build an eight-foot linear knee wall.

When to Build a Knee Wall

Build a knee wall as early in the attic renovation process as possible. A knee wall is considered part of the basic framing of an attic remodel, so it should be one of the first stages in the project.

Safety Considerations

Be careful when working with the circular saw or electric miter saw. Observe the manufacturer's safety instructions.

What You'll Need

Equipment / Tools

  • Electric miter saw or circular saw
  • Hammer
  • Scrap two-by-four, roughly 2-1/2 feet long
  • Pencil
  • Tape measure
  • Utility knife
  • Drywall square
  • Drill

Materials

  • 3 two-by-fours, 8 foot
  • one-by-four, 8 foot
  • 1 drywall, full sheet (4-foot by 8-foot)
  • Nails
  • Drywall tape
  • Joint compound
  • Drywall screws

Instructions

  1. Determine Rafter Angle

    The knee wall will be built on the floor of the attic, and then tipped into place against the rafters. One of the two-by-fours will act as the bottom of your wall, and will not be cut. Determine the angle of the rafters by setting the scrap piece of two-by-four in a vertical position against the side of a rafter.

  2. Scribe and Cut Template

    Scribe a line on your scrap piece along the angle formed by the rafter. Cut on the angle with the miter saw. This is now a template that will be used to cut the other two-by-fours.

  3. Cut Wood

    With the electric miter saw or circular saw, cut six lengths of two-by-fours, each piece 2-1/2 feet long. At this point, you are not cutting at an angle. You just need to break down the two-by-four so it will be easier to manage when cutting angles.

  4. Mark Angle

    Use the template to determine the angle on each of those six pieces of two-by-four. With the pencil, draw a line across that angle.

  5. Cut Angles

    Use a miter saw to cut each two-by-four on the angled marks. Be precise. A two-by-four that is too long or too short will throw off spacing for the rest of the two-by-fours.

  6. Attach Short Two-by-Fours

    On the long two-by-four, measure and mark every 16 inches. Nail the short two-by-fours perpendicular to the long two-by-four every 16 inches on center. Make sure that you have one two-by-four at each end.

  7. Nail One-by-Four

    Keeping the knee wall still upright, nail down the 1x4 across the top of the angled boards with the nails.

  8. Place Knee Wall

    Push the knee wall firmly into place. Nail down the sole plate (the bottom of the wall) in several places on the attic floor.

  9. Attach Knee Wall

    Do the same thing for the angled top of your knee wall, nailing it into the rafters in several places.

  10. Install Drywall on Knee Wall

    With the tape measure, measure the height and length of the knee wall. Use the utility knife and drywall square to measure these dimensions on the sheet of drywall. Lay the cut drywall against the drywall. Screw the drywall into place with drywall screws.

    For an 8-foot section, there should be no drywall seams. But if you do extend the knee wall, you'll need to install multiple, adjoining sheets of drywall and cover the seams with drywall tape and joint compound.

When to Call a Professional

A carpenter or contractor can build a knee wall for you if you unsure about your carpentry skills, ability to haul materials up to the attic, code requirements, and any other factor.