How to Build a Knee Wall in an Attic

Knee wall exposed in the attic

bptakoma/Flickr/CC BY 2.0

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 a useful 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.

Difficulty: Average

Time Required: Three hours

What You Need

  • Three 2x4s
  • 15 penny nails
  • One 1x4 (eight feet long)
  • One sheet drywall
  • Miter saw
  • Hand saw
  • A piece of scrap 2x4, roughly 2 1/2 feet long
  • Carpenter's pencil

Instructions

  1. The knee wall will be built on the floor of the attic, and then tipped into place against the rafters. One of your 2x4s 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 2x4s perpendicular to your long 2x4 every 16 inches on center.
  6. Keeping the knee wall still upright, nail down the 1x4 across the top of the angled boards with the five penny nails.
  7. Push the knee wall firmly into place. Nail down the sole plate (the bottom of the wall) in three or four places into the attic floor.
  8. Do the same thing for the angled top of your knee wall, nailing it into the rafters in three or four places.
  1. Face the knee wall with the appropriate size of drywall.