How To Insulate Attic Drop-Down Access Stairs

Even if your attic is well-insulated, the folding stairs you use to access it can be a significant source of heat loss. They’re often poorly sealed and provide only a thin piece of plywood to stop warm air. Cooler air from your air conditioner can also seep through gaps around the door.

Sealing and insulating your attic’s access stairs can improve comfort and lower utility costs. One way to accomplish this is to buy a premade cover, like the Attic Tent, that you can install in minutes. However, you can save money and build your insulation box with just a few supplies and 1–2 hours of your time.

Materials and Tools

You’ll need these materials and tools for the project:

• ¾” x 4′ x 8′ sheet of rigid foam board
• 2″ x 30′ roll of foil tape
• Two ¾” x 17′ rolls of foam tape weatherstripping
• Tube of caulk (optional)
• Tape measure
• Utility knife
• Framing square

When you’re at the store, look specifically for foil tape. Regular duct tape or painter’s tape won’t hold up to the heat in the attic.

Sealing the Attic Stair Opening

Start by checking to see if the attic stairs close tightly. If you see visible gaps when the stairs are closed, you may need to make some adjustments to achieve a snug fit.

Then, except on the hinge end, apply the foam tape weatherstripping around the perimeter where the plywood door meets the frame. The weatherstripping creates a tight seal between the attic door and frame.

Building the Insulating Foam Box

Once you’ve sealed the opening, you’re ready to build the foam box. You’ll make the shape from the foam boards, then seal it with foil tape.

Measuring and Cutting the Foam Board

Next, verify how much you need to cut from the foam board. Use a tape measure to verify these two measurements:

• The dimensions of the attic stair opening
• The height of the stairs protruding over the attic floor

Using your utility knife and framing square, cut strips from the board that are 1–2 inches wider than the stairs and extend above the floor. 

Use a new blade for the cleanest, most precise cut. Finish the cuts by bending the foam and cutting from the other side. The two-sided cut helps keep the edges straight, making for tighter seams.

Finally, cut a piece of foam the size of the exterior box dimensions. This piece will be the insulating box’s “lid.”

Assembling the Box Frame

Once you’ve cut all the pieces, you’re good to assemble the box frame.

Join the corners of the foam strips with foil tape to form the box shape. Run a bead of caulk along the joints for an extra-tight seal if desired.

Installing the Insulating Box

With the frame constructed, it’s time to install it over the attic stairs. You’ll also attach the lid in this step to complete the box.

Preparing the Installation Area

Before installing the box, sweep the attic floor around the stair opening so the tape and caulk adhere properly. Attach foam weatherstripping tape to the bottom edge of the box where it will meet the attic floor.

Positioning and Sealing the Box

Position the box squarely over the attic stair opening. Press firmly to guarantee good contact between the weatherstripping and the attic floor. Then, run strips of foil tape around the edges to seal the box to the floor.

Caulk around the inside attic stair framing can be an extra sealant layer. You should also use caulk to patch gaps in the frame.

Finally, attach the lid to the box. Use a piece of foil tape along one side, but leave the other sides free to open it like a hinge. 

Maintaining the Insulation Box

After you’ve installed your DIY insulation box, periodically check to see that it hasn’t shifted or come loose. Refasten any loose foil tape, and replace worn or damaged weatherstripping.

Whenever you access the attic through the box, close the lid. To make the job easier, you can attach a long enough cord or rope to the underside of the lid.