Attic hatches and folding stairs

Posted Wednesday, January 25, 2012 in Sustainable Maine

Attic hatches and folding stairs

by Paul Kando

Attic hatches and stairs are champion air leakers. The majority I have seen during energy audits were not insulated and virtually none have been weatherstripped. Hatch covers are often made of some leftover piece of sheet good casually thrown over the access hole to the attic, on the grounds that it is seldom used. Big mistake. As we discussed on numerous earlier occasions, leaks into the attic convey not only expensive heat lost from the house but also airborne moisture which can cause severe damage when it condenses.

Luckily, attic hatches, with or without folding stairs, can be easily sealed and insulated. Use your imagination and take advantage of the fact that, unlike doors, these openings are horizontally oriented. Here are a few easy-to-execute ideas, all well within the capability of any weekend carpenter.

Follow these simple rules:

(1) Use materials sturdy enough to do the job: 3/4-inch plywood is better than half-inch plywood, and forget about that piece of salvaged quarter-inch louan, sheetrock, or 7/16-inch OSB.

(2) Attic access openings must be properly insulated. Just like a cold window glass, an uninsulated hatch or stair cover is likely to be a site of condensation.

(3) When closed, the access cover must seal well, so no air can pass around it.

(4) A folding attic stair can be sealed only by adding a separate hatch cover above it. There is no room for insulation on the plywood facing of a folding stair but it won’t hurt to weatherstrip it anyway. To accommodate the folded stair, you may need to construct an insulated box sealed to the attic floor. The top of this box will serve as the hatch cover.

(5) Whether humble scuttle hole or folding stair, build the hatch cover to easily open and close. You should not need to remove a half-dozen screws to get up there. If you do, chances are the cover will not be put back properly. You went up there for some reason and will be busy with that. So you will be likely to hurriedly pull the cover over the hole, intending to come back later to screw it back in place. Likely as not you will forget to come back and do it. Even if you are more disciplined than that, why make it a royal pain to go up to the attic?

In my opinion the best material to insulate these openings is rigid foam board. It is dimensionally stable, lightweight, can be stacked in multiple layers (you can even use spray foam to hold the layers together) and, importantly,  you won’t get showered with bits of insulation every time you open the hatch. I would not consider less than 4 inches of foam board here.

Weatherstripping of attic hatches is essential but it does no good unless the cover closes tightly against it. Take advantage of the horizontal orientation of the access hole: Use soft foam weatherstripping (half-inch-thick is a good choice) and use the weight of the closed hatch cover to compress it. Don’t forget to seal around the hatch opening in the attic. Many a hatch leaks air around the outside trim because of a gap between the rough opening and the hatch frame —  another good spot for condensation, mold and mildew. This kind of leak is a frequent problem around windows and doors as well.

A self-explanatory illustration is provided to serve as inspiration. It came from a government web page. Apologies for the misspelled legend: Shopping for “ridged” foam is likely to be a frustrating experience. What you want is rigid foam board.

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