Attic Insulation

Summary: Home insulation done properly will save on your heating bill, but may not be as simple as you think. Read about Blanket Insulation, Rigid Insulation and Reflective Insulation to decide which is right for you.

Home insulation comes in many forms, each of which performs its own purpose depending on where you’re putting it. Blanket insulation comes in large rolls and resembles quilt batting. Blanket insulation comes in several widths to fit between wall studs and attic and floor joists – so provided your home was built by current standards, all you have to do is pick up the right size insulation and roll it out.

Blanket insulation can also be purchased with a vapor barrier in place, something you’ll need to know about later.

Rigid insulation is made of plastic or other fibers. It’s lauded for its strength and acoustic – as well as thermal – insulation. Blown in insulation is cool stuff: special fibers or pellets are pneumatically sprayed into walls, attics – just about anywhere you can’t reach. Foamed-in-place insulation gets points for being just plain cool: an insulation professional comes into your home to measure, meter, mix, and spray polyurethane foam to your home’s specifications.

Reflective insulation systems (sometimes called a “radiant barrier” depending on where in your house you use it) are comprised of aluminum foils with any number of backings. Having a reflective side makes RIS effective in only one direction, primarily reducing downward heat flow.

But proper insulation isn’t as easy as just picking a type and slapping it up (or in or on).
It’s time for some math. It’s time for R-Values.

R-values measure how well a particular insulation resists heat or cold. In theory at least, the higher the R-value, the better the insulation, which in turn will lower your indoor climate control bills. At first glance, some of the tables and charts might make you dizzy, but the US government has come to the rescue with its computer program called Zip-Code. Named for postal zip codes, this program lays out all of the variables that need to be identified in order to recommend the best insulation for your home. By entering the first three digits of your zip and where in your home you plan on insulating, ZIP-Code gives you the recommended R-Value based on regional weather and climate.

So you’re set now, right? Well, pretty much. Just keep in mind that like all things none of this is absolute. For instance, the University of Colorado School of Architecture built two identical structures with the same rated R-Value and insulated one using fiberglass, and the other using blown-in cellulose. While initial tests showed the overall effectiveness of the cellulose to be better than that of the fiberglass, its real muster was proven after three weeks when it was discovered that the building insulated with the cellulose used 26.4% less energy than the fiberglass insulated building used. So while both buildings used recommended R-Values based on the ZIP-Code system, blown-in cellulose came out the clear winner, primarily because it is air-tight.

So if you’re looking to knock some dollars off of your heating bill, or you’re just sick of sitting around reading the paper, wearing two pairs of long underwear and three sweaters, insulating your home is the most cost effective place to start.

Typical R-Values

MATERIAL R-Value
1” thick hardwood siding 0.91
Lapped wood shingles 0.87
4” thick brick 4.00
Filled core concrete block 1.93
3.5” thick fiberglass batting 10.90
6” thick fiberglass batting 18.80
1” thick fiberglass board 4.35
1” thick cellulous fiber 3.70

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