Unless you have a walk-in attic, chances are that your attic access is some sort of trap door in the ceiling, likely fitted with a set of fold-down stairs. And even if your attic is insulated (and it should be), chances are that the trap door itself is not. That’s a problem.
There’s nothing to stop that expensive climate-controlled air—heated in the winter, cooled in the summer—from escaping through the trap door. It’s like having a slow leak in your bank account.
The good news is that it’s a relatively easy fix.
The easiest hedge against a thermal leak is to cover the backside of the trap door with fiberglass insulation.
- Cut the batts to overhang the sides a bit. (You may need two pieces to cover the entire door.)
- Place the insulation against the door with the fiberglass side facing down, and staple it to the door.
- Although it’s tempting, don’t compress more than one layer onto the door— fiberglass is most efficient when its fibers aren’t compacted.
It’s also a good idea to apply adhesive-backed weatherstripping to the perimeter of the door side that closes on the framed opening. This will help keep conditioned air from leaking into the attic.
Fiberglass will help, but a more effective long-term fix is to make a box from rigid insulation that fits over the door’s framed opening (and the folded stairs, too, if you have them). Rigid insulation is more efficient than fiberglass, and the box will be more air-tight than fiberglass, too. Win-win.
You’ll want the insulation with the highest R-value (the capacity of insulation to resist the conductive flow of heat). You’ll only need one sheet to build the box.
There are three types of rigid insulation:
They’re all available in 4x8-foot sheets; if possible, buy the 2-inch-thick stock.
- Expanded polystyrene (EPS) that’s rated at R-3.8 per inch of thickness
- Extruded polystyrene (XPS) rated at R-5 per inch
- Polyisocyanurate (Polyiso), rated at R-6.5 per inch
To make the box, you’ll need:
- Measuring tape
- Knife or saw to cut the insulation
- Packing or duct tape
- Caulk gun
- Construction adhesive
- First, go into the attic. If you have fold-down stairs, pull them up into the attic. Measure the door’s framed opening and, if needed, the height of the folded stairs above the framed opening.
- Now, transfer the measurements to the sheet of rigid insulation.
- Mark out the sides of the box that will correspond to the framed opening (two long, two short), and if there are stairs, make the pieces’ width a couple of inches wider than the height of the folded stairs, so that when closed, the stairs won’t hit the box.
- Apply construction adhesive to the ends of the four pieces and form a box. Check to make sure that the box is the same size as the framed opening. Use tape to secure the corners until the adhesive dries.
- From the remaining insulation, cut a rectangle that’s the length and width of the box. Attach it to the box with adhesive and tape.
- When the adhesive has dried, the box is ready to be fit into place in the attic. Place it on top of the framed opening and close the door.
- If you favor the belt-and-suspenders approach, you can also add a strip of adhesive-backed weatherstripping to the bottom edges of the box to seal any potential leaks.
Attic Stair Insulation Alternatives: Foil and Attic Covers
Of course, there are also commercially available alternatives. Check your local hardware store or home center for attic stair insulation alternatives and you’ll find everything from readymade tents of reflective foil to fancy covers made from 2 3/4-inch-thick expanded polystyrene (EPS).
You’ll also find pre-cut kits that you can assemble yourself. Most are available in different sizes to fit varying configurations of attic doors. And don’t sweat the money—in the end, you’ll be saving more than you spend.