Wednesday, October 14, 2009

How Much Attic Insulation is Enough?

I wondered exactly how much insulation I had in the attic. It’s a good thing to know because the proper amount of insulation improves your home's energy efficiency, it’s environmentally friendly because good insulation allows you to use less energy from the power plant to heat and cool your home, and it also saves you money.

And I’m all about saving energy and saving money even after I completed the 20% Energy Reduction Challenge Project.

I grabbed a flashlight and a yardstick and climbed into the attic. My plan was to stick the yardstick next to the insulation and find out how many inches deep it is. Then I can determine the insulation’s R-value. R-value is a rating that indicates how effective the insulation is. The larger the number the more effective the insulation.

Turns out I didn’t have to go to all that trouble. My builder had a yardstick of sorts stapled to a rafter. It was easy to see that I have 13 inches of loose fill insulation in my attic.

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But what is the R-value of the insulation in my attic?



If I had loose batt insulation (it generally comes on a roll) the R-value is usually printed somewhere on the insulation. Since mine is blown insulation, I have to determine the R-value by number of inches of insulation.

Fortunately the builder also stapled a chart showing me how many inches of loose fill insulation determines it’s R-value. The blown insulation in my attic is 13” thick which means it has an R-value of 38.

But how much insulation should I have in my attic? Is the insulation I already have in my attic enough?

I did a lot of research. Determining how much insulation you need depends upon four things:
  • Where you live — colder climates need a higher R-value than warmer climates (obviously)
  • The age of your home — the older the home, the less likely it is to be insulated 
  • How your home is built — the type of materials used, if it is built on a concrete slab or has a basement, how many stories, etc. 
  • How you currently heat and cool your home — if you use natural gas, electricity, or propane heat,  have a central air conditioner, etc.
The US Department of Energy has a state by state map that shows the recommended R-value levels for new wood-framed buildings. According to this map I should have insulation with an R-value of R30 - R60 in my attic. Personally I think that’s a lot of wiggle room. I don’t want to under insulate, but I don’t want to overbuy insulation if I don’t have to (Hi Recession!)

I already have insulation with an R-value of 38 in my attic. Which is the minimum code requirement. But as I do more and more home improvement projects I find that Mike Holmes philosophy on minimum code requirements is almost always true:

Do you buy a car that has minimum tires, minimum engine, minimum seat belts? No we don't, we want to buy better. I think the issue with new homes and older homes is not knowing if the minimum code is enough. Well I've proved it over and over again that it's not.”

So I have to wonder if R38 of insulation in my attic is really enough.
To get the specifics I used the U.S. Department of Energy's Zip-Code Insulation Program to tell me what the recommended amount of insulation is for maximum energy efficiency for homes in my zip code. I entered my zip code, type of furnace I have (natural gas), and some other basic information about my home into the on line form.

It recommended that for maximum energy efficiency, the insulation in my attic should have an R-value of 49.

Looks like I inadvertently added another thing to my Do It Yourself Honey list.


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