How to Build a Knee Wall in Attic

Knee Wall Exposed In Attic
CC-Licensed; Flickr User bptakoma

A knee wall is a quick way 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 useful space, and it helps to insulate your attic space against air infiltration from the outside. Instructions will build an eight-foot linear knee wall.

Difficulty: Average

Time Required: 3 hours

Here's How

  1. Knee wall will be built on the floor of the attic, and then tipped into place against the rafters. One of your 2x4's will act as the bottom of your wall, and will not be cut. Determine the angle of rafters by setting the scrap piece of 2x4 in a vertical position against the side of a rafter. Scribe a line on your scrap piece along the angle formed by the rafter. Cut on the angle with your miter saw. This is now a template.
  2. Cut six lengths of 2x4, each 2 1/2 feet long.
  3. Use a template to determine the angle on each of those six pieces of 2x4; draw a line across that angle.
  4. Use a miter saw to cut each 2x4 on that angle.
  5. Nail those short 2x4's perpendicular to your long 2x4 every sixteen inches on center.
  6. Keeping the knee wall still upright, nail down the 1x4 across the top of the angled boards with the 5 penny nails.
  7. Push knee wall firmly into place. Nail down the sole plate (the bottom of the wall) in 3 or 4 places into the attic floor.
  8. Do the same thing for the angled top of your knee wall, nailing it into the rafters in 3 or 4 places.
  1. Face knee wall with the appropriate size of drywall.

What You Need

  • Three 2x4's
  • Ten-Penny Nails
  • One 1x4 (8' long)
  • One Sheet Drywall
  • Miter Saw
  • Hand Saw
  • A piece of scrap 2x4, roughly 2 1/2 feet long
  • Carpenter's pencil
  • Five-Penny Nails