Construct an Attic Stairs Cover Box

Written by The U.S. Department of Energy's Office of EERE
Sat, Feb 27, 2010

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To insulate your attic stairs access, you can construct a lightweight, moveable box that will rest on the stair frame from the attic side.

Pay careful attention to inside and outside dimensions plus height requirements for the specific measurements of the attic staircase being installed. The cover box should rest squarely on top of the attic stairs frame. Shim and seal the gap between the frame and rough opening and install weatherstripping.

Materials Needed

You'll need the following materials to construct an attic stairs cover box:

4x8 foot sheet of 1/2-inch rigid foam board or fibrous ductboard insulation
Insulation batt (optional)
Duct sealing mastic or construction adhesive
1-inch roofing nails (8d or 16d)
Tape measure, sharp utility knife, and straight edge; or table/circular saw
Weatherstripping or gasket material with adhesive.

Instructions

Use the template in the illustration below to cut pieces from a single, 4X8 foot sheet of 1/2-inch rigid insulation for a box 53 1/2-inches long (51 1/2-inches inside), 24 3/4-inches (22 3/4 inches inside), and 9 inches of depth inside. The box will fit stairs with an outside framing dimension of 53 1/2 inches by 24 3/4 inches. Adjust dimensions to fit the specific stairs being installed. Carefully measure both the inside and outside dimensions to the appropriate length, width, and depth clearances to cover the box.

Template showing the following pieces cut from a 4 foot by 8 foot sheet of half-inch rigid insulation for a box 53 1/2-inches long (51 1/2-inches inside), 24 3/4-inches (22 3/4 inches inside), and 9 inches of depth inside: Two end pieces, 9 1/2 inches by 24 3/4 inches; two small end pieces, 9 inches by 23 3/4 inches; two side pieces, 9 1/2 inches by 52 1/2 inches; two small side pieces 51 1/2 inches by 2 1/2 inches; one cover piece, 52 1/2 inches by 23 3/4 inches; one brace, 23 3/4 inches by 2 1/2 inches. The caption reads: All pieces can be cut out of a 4 foot by 8 foot sheet of rigid insulation. Use a table saw for smooth, accurate cuts.

Create the box as shown in the illustration below:

Apply adhesive/mastic and use roofing nails to construct the two end and two side pieces.
Assemble the side and end pieces into a box using adhesive and longer nails.
Add the center support brace and cover piece with glue and nails.
Glue a faced insulation batt to the cover piece with adhesive applied to the paper backing (optional).

Diagram showing the construction of an attic stairs cover box using the materials cut from the template above. The larger side and end pieces form the outside of the box, and the smaller side and end pieces fit inside to form a second layer. The brace is placed in the cutouts in the smaller side pieces, and the cover drops into the top of the box. The length between the outside edges is 53 1/2 inches, and the width is 24 3/4 inches. The length between the inside edges of the outer layer of board is 52 1/2 inches, and the width is 23 3/4 inches. The length between the inside edges of the inner layer of boards is 51 1/2 inches, and the width is 22 1/2 inches. The box is secured together with one nail at each corner, one nail on each end of the brace, and three nails on each inside end board. The caption reads: Assemble side pieces, end pieces, and brace as shown. The cover piece will drop in and be attached with adhesive and nails.

Article source: The U.S. Department of Energy’s Office of Energy Efficiency and Renewable Energy (EERE). For the most up-to-date information please visit the EERE website.