Here in Phoenix we are always looking for ways to help stay cooler and reduce our homes energy costs. One area that could use improvement in many homes, especially older homes in the Phoenix area is the attic insulation. Below is a guide to help determine if it would be financially advantageous to upgrade your attic insulation. The R values are estimates, different types of insulation have different R values per inch.
If your home was built before 1979 and the insulation has not been upgraded since then, you could probably save significantly by increasing the amount of insulation in your attic. During this time energy was cheap so insulation wasn’t much of a concern. When I’m doing home inspections in Phoenix on homes this age, I typically find between 2 to 4 inches of insulation which is equal to about R-11 depending on the type of insulation installed.
If your home was built between 1979 and 1984 you could probably save moderately on your energy bill by adding insulation in your attic. Typically I find between 5 and 8 inches of insulation in the attic when doing home inspections in Phoenix on homes this age, this is equal to approximately R-19 depending on the type of insulation installed.
If your home was built after 1984, your attic insulation probably meets current standards. Adding insulation would probably not be the most cost effective way to save on your energy bill. Typically on homes of this age we see anywhere from 8 to 14 inches of insulation which is from R-30 to R-38.
Estimated R values per inch for common types of insulation:
- Blown in cellulose R-3 to R-3.8
- Blown in fiberglass R-2.5 to R-3.7
- Fiberglass batts R-3.1 to R-4.3
- Spray foam R-3 to R-7 (depending on type)
Another great source for information is the APS Energy answers publication on wall and ceiling insulation, click here to view.