Monday, October 4, 2010

It's Good For You, But You Can't Eat It!

We just finished applying spray foam insulation to the green home we are building at 631 James Alexander Way in Davidson.

Spray foam insulation is the bomb! I remember saying that when I was interviewed by about the first LEED-certified home we built (233 Catawba Avenue in Davidson). I got this sheepish expression on my face because I realized it sounded silly coming from a 46 year old.

But, spray foam insulation truly is the bomb. What makes it so special?

The house on Catawba was the first time I used spray foam insulation. Once it was applied, the house suddenly got quieter. And cooler, even though it was still the middle of summer. The homeowner noticed it too.

Inch for inch, spray foam (we use an open cell product called Icynene) is only marginally a better insulator than fiberglass batt insulation. The R-value (r-value being a measure of the insulating quality of a product) of spray foam is about 3.7 per inch, compared to about 3.1 per inch for fiberglass batt insulation.

What makes spray foam a superior product is that it also provides a tight air seal when it is applied. The product is applied in a thin layer, but it quickly expands to 100 times it's size. As the photo shows, spray foam complete fills the cavity in the framing. By contrast, fiberglass loosely fits into the wall, and air can easily pass through it. It's like being outside in the cold with the same jacket, but in the spray foam world there is no wind, and in the fiberglass world the wind is blowing at 30 mph. Obviously you're much more comfortable without the wind. A house insulated with spray foam is several times tighter than one with fiberglass batt insulation, and as a result it takes less energy to heat and cool the home.

Spray foam also makes it easier to insulate the underside of the roof deck, and thus to have a sealed and conditioned attic. In fact, fiberglass batts cannot be used for this application. A conditioned attic results in a much more efficient HVAC system since the ductwork and equipment that is typically found in the attic is within the conditioned envelope of the home. Instead of a typical attic where the air inside your ducts can warm up by 10 degrees by the time it gets to the room, in a conditioned attic there is no change in temperature as the cool air passes through the attic.

Another benefit of spray foam insulation is that kids love it! My two children like to take the scrap pieces of spray foam and beat each other over the head with them, and they always ask if they can eat it. It's probably better to eat than fiberglass but no, you can't eat it!

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