Insulate your Attic stairs

The silver is the insulation

While everyone knows the importance of having insulation in your attic (you should definitely know this) some might overlook the attic stairs.  Fellow blogger Allison Bailes covered this issue on Friday in his post "Attic Stairs - A mind blowing hole in your building envelope":

If we have 1000 square feet total of ceiling area, and we put R-38 everywhere but the 10 square feet of the attic pull-down stairs, you may be surprised when you see the answer. (For ease of calculation, I'm going to ignore the effect of the framing in the attic.)

Are you with me? We've got 990 sf at R-38 and 10 sf at R-1. (I'm being generous by assuming that quarter inch of luann plywood plus the air films give it a full R-1.) When you plug those numbers into the equation for average U-value and then convert to average R-value, the answer is R-28. (See the Flat or Lumpy article for details on the math - but be careful!)

No, I am not kidding! Because of that 1% of the attic that's uninsulated, the average R-value for the whole attic drops by 27%. I told you it was amazing, didn't I?

The reason for this is that, although the attic stairs account for only 1% of the area, the rate that heat flows through them by conduction (per square foot) is 38 times higher than in the insulated part of the attic. In other words, the amount of heat that flows through the 10 sf of attic stairs is the same as what flows through 380 sf of the insulated attic. Wow!

Luckily, if you don't currently have insulation on your attic door you have a few options.  One such option is The Battic Door attic stair insulator cover.  This solution reminds me of an insulated hat that covers your stairs. There are different levels of insulation you can get that include weather stripping.

Another option is to get an insulated panel that attaches directly to the attic stair panel.  This is the option my attic stairs employ (seen in the picture at the top of the post).  What I don't seem to have is weather stripping, so I think I'm going to add that.  To build your own attic stair insulation, just go to your local hardware store and see if they have an insulated panel or buy some insulation, cut it to the shape of your attic door (making sure the stairs will fold up into it), and attach to your attic stairs.

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My attic cover is 2-3 feet thick panel when considering the insulation. Thanks for the ideas in this article. I'll replace now with a lightweight insulating panel.
I realized the problem of the attic stairway leakage about four years ago. I bought a device called an attic tent. It installs easily with a staple gun and a caulk gun. I am not sure of its payback but I have noticed when I unzip a small portion of it, I feel the conditioned air moving into the attic. It is rugged and well made and I have been happy with it.
I have interior hollow-core doors that go into my attic at three locations. It's definitely a hole in my building envelope since my attic is not sealed. I'm thinking of using foam insulation board and cutting out the shape of my door and mounting the insulation on the door, around the door frame and putting weatherstripping at the base. Any other suggestions or alternatives?
I don't have stairs, just a hatch. But it has about 18" of insulation stapled on the top and covered with Tyvek. My home inspector also suggested a hook-and-eye closure to pull the hatch down against weatherstripping and further seal leaks. Leak sealing is pretty important too; moist warm air making it up into your attic can cause serious problems with the building integrity, let alone the energy costs... :)
Thanks Chris. This is excellent. Especially the "effect of" calculations.

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