Attic access points can be a mind-blowing thermal liability. If you don’t believe me, open the pulldown stairs or scuttle hole and go into an attic on a cold day. Then turn around and look down through the hole. You’ll most likely feel a strong whoosh of warm air from the house hitting you in the face. That blast of expensive air being lost is courtesy of the stack effect. Air sealing an attic access is one critical part of reducing that thermal liability. The other critical part is insulating the attic access, which I’ll cover in a separate article.
The Building America Solutions Center has a helpful guide on air sealing an attic access, and the image below comes from that site. (I’ve listed two more great resources at the bottom of the article.) Note the locations they indicate for sealing. They use the word weatherstripping, but it could also caulk, spray foam, or a gasket.But you have to be careful. The photo below shows a door for pulldown stairs that have weatherstripping around the perimeter, but there’s still a big hole. The problem here is that builder-grade pulldown stairs sometimes can’t take weatherstripping. If you put it on the hinge side—and you should—there’s not enough space for it and it prevents the door from closing. If you have pulldown stairs like that, you need to do something different.
The best solution to that problem is to put some kind of cover above the pulldown stairs. The photo below shows one called the Attic Tent, which is one of many commercially available attic access covers. Tamarack has two types: the E-Z Hatch and the Battic Door.
In my contracting days, I installed a lot of these. They go in easily with staples and caulk, have a zipper around the edge, and provide a pretty airtight attic access. I also liked them because I could insulate an attic and use that cover to keep the cellulose dust out of the house. The biggest downside to the Attic Tent is that it’s only about R-6.6.
One popular method I’m not fond of is making a box out of rigid foam board to go over the opening. These are often too lightweight to provide a good seal around the edges. You can see a gap around the right side of the foam board box in the photo below. Another problem with this method is that people who use them set them aside and sometimes leave them there because they’re inconvenient.
Building a box out of wood can solve that problem. The photo below shows a well-built wooden box that’s air sealed and heavy enough to keep the top pressed firmly against the sides. I didn’t get a picture of it, but this one also had a latch to make it even more secure.
You air seal a scuttle hole the same way you do pulldown stairs and the comments I made above apply here as well. The Building America diagram below shows the details.The scuttle hole cover below is made of wood with three layers of rigid foam board above. When dropped into the hole, it presses against the weatherstripping applied to the upper side of the trim boards. Wood or drywall can work well here because of their weight. Still, everything has to be cut properly to make a good fit.
Not all attic access points are in the ceiling. Some attic spaces are behind attic kneewalls. When you put a door in those kneewalls, it needs to be weatherstripped to make a good air seal. In the photo here, you can see the black weatherstripping around the full perimeter of the door.
Keys to air sealing any type of attic access
Here are some of the key points to consider when air sealing an attic access:
- Make sure you have a door or cover that can close securely with weatherstripping.
- If the main access doesn’t do that, install a secondary one. These are usually on the attic side, but I’ve also seen them on the conditioned space side.
- One that helps make attic access points more airtight is to have some kind of latch to pull the cover tightly against the weatherstripping.
- Inspect the attic access carefully to find any air leakage pathways that need to be sealed. For house plans, use the pen test.
- Make it easy for occupants to use, including returning it to the sealed position.
Attics can be as cold as the outdoor air in winter and much hotter than outdoor air in summer. Everyone knows about insulating the attic, but many don’t understand how even a small part of the whole ceiling or kneewall can be a tremendous thermal liability. Air sealing an attic access properly is critical to having a robust air barrier.
Building America Solutions Center Air Sealing Attic Access – part of the US Dept. of Energy and one of many helpful pages on this site
Building Science Corporation Attic Air Sealing Guide & Details – Scroll down and look for the pdf download at bottom right.
Southface Air Barrier & Insulation Installation Component Guide – made for the Georgia energy code
Allison A. Bailes III, PhD is a speaker, writer, building science consultant, and the founder of Energy Vanguard in Decatur, Georgia. He has a doctorate in physics and writes the Energy Vanguard Blog. He also has a book on building science coming out in the summer of 2022. You can follow him on Twitter at @EnergyVanguard.
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