Pull down attic stairs are super-sized attic hatches that just beg homeowners to store more stuff in your attic. Besides the issues stemming from the particularly large hole in your ceiling, it creates a storage headache. For homeowners, a storage problem usually means ‘not enough.’ For auditors, this means using space that ought to just be insulation for Timmy’s guitar, his old bike, Legos, his new bike and the unpacked remains of twelve previous moves.
This aside was by way of saying, let’s insulate and air seal that attic pulldown stairs. You won’t stop using the attic as storage, but the wicked draft of cold air around the hatch won’t be missed.
Attic Pull Down Stairs
These are exactly what they sound like: a set of foldable stairs that can be pulled down for easy attic access. They usually come pre-installed with 1″ of foam board insulation that is almost always worn though. I’m not sure if it is pre-installed that way.
The attic access ladders are horrifically leaky. It’s hard to pin down an exact figure as attic hatch air sealing is almost always a piece of a larger project. But under blower door depressurization a pulldown stairs can account for over 10% of the house’s CFM50.
It is notoriously hard to quantify how much heat loss occurs through big building envelope holes like pulldown stairs. Our main quantitative tool, the blower door, forces a very abnormal condition from which it is difficult to extrapolate ‘normal’ conditions. Best to just find the biggest holes and seal them.
How to Insulate and Air Seal Attic Pull Down Stairs
As a first thing, there are pre-fabricated foam board enclosures for pull down attic stairs available, like this guy on the left. When purchasing make sure that the length and width match those of your attic stairs.
Air Sealing the Trim – A quick confession…this is directly copied from a previous post on sealing attic hatches. But the job is identical.
The first step is air sealing the finish trim and enclosure around the attic stairs. Carefully pull down the finish trim (and like I usually note, pray the builder used staples or finish nails and not, say, ring-shank nails).
Using caulk for smaller gaps (less than 1/4″) or foam sealant for larger ones, seal the gap between the stairs framing and the rough cut drywall. (I have to be just a shade vague there, as the drywall can either butt up against the hatch frame or lap over it).
Apply a bead of caulk on the inside and outside edges of the trim, and then reattach it.
Install a Weatherstrip/Gasket – Once the trim and frame are airsealed, install either a heavy bulb weatherstrip or a sealing gasket (like on your refrigerator). The gasket/weatherstrip would be installed on the top edge of the studs framing the pulldown stairs.
The Coffin (not to sound too ominous) – After installing the gaskets, build a plywood ‘coffin’ to fit over the pulldown stairs in the attic. Measure the dimensions so that the interior perimeter is flush with the inside edge of the framing studs. Attach hinges to the box on the rear exterior (behind you as you walk up) fastened to the framing studs.
The end result should be such that you can walk up and easily open it. Some people incorporate a weight and pulley fastened to the overhead rafters to act as a counterweight. If you have a high level of blown insulation (18+ inches of loose fiberglass or cellulose, you may need to build a dam from plywood or foam board around the pulldown stair. I mean unless you enjoy big face fulls of insulation.
Insulate – Add insulation to the exterior of the plywood box. Since with attic insulation, we gun for a pretty high standard (at least R-49), the coffin insulation should match. at least 4″ of foil faced polyisocyanurate should be glued to the box though 6″ or 8″ isn’t uncommon
Pull down stairs provide very convenient access to an otherwise unusable space. Homeowners use them to store vital unpacked boxes and old books. Sealing and insulating the attic pull down will at least make this a less egregious hole through the building envelope.