To insulate the access to the attic stairs, you need to make a lightweight box that can move and rest on the stair frames. When you measure the inside, outside and height measurements on YOUR specific staircase that YOU want to install. The important thing is that this box should rest squarely on top of the attic stairs frame.
You'll need the following materials to construct an attic stairs cover box: (Source: US Department of Energy Efficiency and Renewable Energy)
- 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. Sealing When built, don?t forget to shim and seal the gap that will be between the attic framing. Around the opening or the area where you get into the attic, you need to install weather stripping. Hardware Store Any major hardware or home related store should have at the materials you need in stock. Call ahead if your aren't sure your local store does so you don't waste the gas. If you don?t want to go to the hardware store (for some reason) go onto the internet and use the keywords attic stair cover and you will find great information about the pieces you need and where to get them. Good Luck in your efforts to Build An Attic Stair Cover. More tips on sealing attic air leaks: The US Department of Energy (USDOE) has a great step-by-step do-it-yourself guide to anyone that would be interested in building their own attic stair covers. Or try this step-by-step video on how to build an attic stair cover.