Sealing in savings
This shows the assembled Battic Door cardboard box over the attic entrance opening. When the stairs are unfolded and you are entering the attic, just lift off the box and place it to the side.
Builders don't always insulate and seal attic access opening covers. Most often, just a piece of plywood or drywall is cut somewhat close to the correct size and placed in the opening, resting on a strip of molding. That type of cover's insulation value is less than R-1 and it leaks air like a sieve. But because the attic access is often in the ceiling of a bedroom closet or a hallway, the air leakage and heat loss/gain are seldom noticeable.
The simplest fix is to attach both insulation to the cover's top and weatherstripping underneath where it rests on the opening's lip. Measure the cover to make sure it fits the opening, with the cover overlapping the molding lip so the weatherstripping seals well. If you have to make a new one, a piece of ½-inch drywall works well and is fire resistant.
The insulation on the cover's top should be up to the recommended code ceiling R-value for your area (check yours at ornl.gov/~roofs/Zip/ZipHome.html). Going above this level will not help appreciably.
Before you add weatherstripping to the molding lip, place the cover over it and check whether it's even (for a good seal). The lip often consists of pieces nailed to the sides of the opening and aren't level.
In my own house, I first nailed a piece of ½-inch drywall to the plywood cover to give it additional weight. Next, I glued a few layers of ¾-inch polyurethane foam sheets on top of it. I added four layers to get three inches of foam insulation. I used foil-faced insulation so it would reflect the heat from the hot roof back up during the summer.
The next step: attach adhesive-backed foam weatherstripping to the top edge of the lip around the opening. Use as thick a foam as you can find to accommodate any out-of-level edges. The weight of the plywood and drywall should compress the foam weatherstripping.
If you want to install pull-down stairs or a ladder — or if your attic currently has one — buy a special insulated cover for the attic access opening. You could attempt to make one yourself, but its weight may be hazardous to open and manage when you are on the stairs.
One of the least expensive options on the market is basically a three-sided heavy duty cardboard box. It's easy to open and assemble, and then you attach your own insulation to the top and sides. It's easy to lift and handle on the attic stairs.
An efficient option is a lightweight, large, rigid-foam domed device that covers the folded stairs or ladder from above. It's strong, and the foam provides adequate insulation. Another design uses a flexible zippered insulated cover that is permanently attached to the attic floor for a good, airtight seal. The zipper provides a large opening for easy access to the attic.
For videos on this subject, visit energysavings.togetherwesave.com/watch-and-learn and click on the Sealing & Insulation tab, then scroll down to find how-to videos on insulating attic hatches and attic pull-down stairs. (If their click-on boxes aren't visible, move your mouse over and down past the first few video boxes until the attic ones appear.)