Many people wonder how much it costs to add additional insulation in their attic, and also wonder how much they need in order to bring their attic to a good R-value. The first place to start is to understand what R-value means to begin with.

What is R-value?

R-value is a measure of resistance to heat flow throughing a specific material. Say what?! English please! Basically the thicker and deeper your insulation is, the higher the R-value. However, it’s important to understand that recommended R-values are based on climate zones. 

What is a Climate Zone? 

There are seven climate zones in the United States that Building Codes are based on in order to achieve maximum energy efficiency and savings when building a home. 

The Phoenix Metropolitain area is in Climate Zone 2. For Climate Zone 2, the recommended R-value is R-38. If you exceed this R-value for our Arizona climate, you get to a point of diminishing returns, negligible savings, and not much added benefit for comfort. 

So How Much Insulation Do I Need to Add in My Attic?

There are a few easy steps you can take in order to figure out how much insulation is in your attic or to figure out what your existing attic R-value is. 

  1. Grab yourself a headlamp, tape measure, respirator mask and get in your attic!
  2. Make sure to only step on the 2X4s (don’t step on your drywall and go through your ceiling)!
  3. Determine what kind of insulation is in your attic. Don’t know? Here’s a quick guide. 
  4. Measure how many inches of insulation you have in your attic. If it looks really uneven with high mounds in certain areas, and lower levels in others, take an average depth measurement.
  5. Determine R-value. To do this simply follow the chart below!
TypeAverage R-Value / Inch
Blown Fiberglass2.5
Blown Cellulose3.4
Fiberglass Batts1.25