Heating and cooling makes up more than half of a typical home utility bill. A high-impact, low-cost way of making cool air last longer is through insulation. A well-insulated home’s utility bills can be 30% lower than those without. Most homes aren’t well-insulated — 80% of those built before 1980 have less than the recommended level of insulation, according to the U.S. Department of Energy. Here in Texas where the sun beats down on the roof and elevates attic temperatures, making sure the attic is well-insulated has a great impact on A/C usage.
How much insulation should I have?
It depends on where you live. Insulation is rated in R-values, which is a measure of heat transfer. The higher the better. Check out this map and chart from the DOE:
Where I live I’m supposed to have R49 in the attic.
How do I know the level of attic insulation I have now?
If you have an unfinished attic with an access door you can pop up into, take a ruler and a flashlight and make note of what you see. Here’s a link to a chart that you can check to find out what you have in your attic.
I have about 5 inches of blown-in fiberglass insulation, which equals about R15. An interesting rule of thumb is that to get to R38, which is recommended for a lot of people, it would take 10-15 inches of insulation, depending on the type.
What do I need to add?
Subtract the R-value you determined you have from your recommended R-value, and that will give you the amount it would make sense for you to consider adding.
There are several approaches to adding insulation. You can hire someone to do it, which will cost from 25 cents to $1 or so per square foot installed, depending on the amount and type added, or you can do it yourself. Home centers sell the blow-in cellulose kind for $6-7 per bag. The R-value you get out of a bag depends on how thickly you blow it in. At R13 thickness, one bag covers 40 square feet. Thus, for my 2000 square foot home, adding R13 insulation would require 50 bags. When you buy more than 20 bags, the home center will rent you the blower for free.