You could be losing 27%(almost a third) of the insulation's effectiveness in your attic!
There are many homeowners who may have this very condition in their attic. Both checking if you have the problem and the fix are fairly simple. When you read this information you'll also realize that it's worth it.
I know we sell HVAC systems which address a big portion of comfort and energy efficiency, but we wouldn't be telling the whole story when it comes to these important topics. It's why we include related information to help homeowners get the 'Biggest Bang for their Buck'.
So, I realize that normally you should have the recommended R-38(r-value) of insulation in your attic, however, according to the building science experts, when you have just 1% of your attic space UNINSULATED, you lose 27%(almost a third) of the effectiveness.
Here's how they explain it:
This problem shouldn't be that hard or expensive to fix. Let's look at an attic that's 99% of the space has the right amount of insulation and only 1% has little to nothing. In this case, the 1% is from the attic pull-down stairs, which typically have no insulation.
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!
Also, what I'm talking about here is just the heat that flows through the solid material, not all the extra heat that leaks through the gaps around the edge of the attic stairs. Remember, the building envelope has both insulation (to limit heat flow by conduction) and an air barrier. I'm just talking about the former here.
So, what're you going to do? Add more insulation to the rest of the attic and bring it up to R-49? Or find a way to insulate the attic stairs? The answer's obvious, isn't it?
First check to see if your attic access is over your conditioned (heated and cooled) space. Then take the steps to insulate it correctly; and start saving money.