Evaluating Your Home Insulation

Dori Wittrig April 5, 2021

When you own a home in the Sonoran Desert, one thought frequently runs through your mind: How can I keep my home cool and my electric bill down?
But before you spend money on adding insulation, there are a few things you should consider. Let’s begin with the R-Value. The R-value is a measure of how well building insulation can prevent the flow of heat in and out of a home. A higher R-value indicates greater insulation performance which results in more energy savings for you but can also mean a higher price point at checkout.
The R-value is given per inch of thickness. In addition to thickness, it also takes into consideration the type and density of the material.
However, your home does not necessarily need the highest R-value insulation. In the Sonoran Desert, Home Depot recommends the following:
  • Attics: R30 to R60
  • 2×4 Walls: R13 to R15
  • 2×6 Walls: R19 to R21
  • Floors: R13
  • Crawlspaces: R13 to R19
Many homeowners think adding insulation to their attic will be the magic solution to lowering their electric bill. This would be true if you have a home that was built before 1984. But newer homes in the Sonoran Desert are insulted to ratings of R30 to R38 already. To increase your attic ceiling above that will not provide a good return on your investment.
Only 15% of your air conditioning costs depend on what is in your attic. An overkill of insulation materials is expensive and offers few added benefits.
If you are considering a radiant barrier, they can benefit an attic that has very poor insulation if installed properly. These barriers are expensive and can take decades to pay for themselves. Radiant barriers are not rated by R-values.
Some homeowners think they can keep their home and garage cooler by insulating the garage. This is not a cost-effective project. Your garage floor absorbs a tremendous amount of heat, especially when you park a car with a 400-degree engine in it. In addition, hot air leaks around your uninsulated garage door. Exhaust fans will burn kilowatts without benefit, opening your garage door in the wee hours of the morning can help temporarily, but then you open the door for snakes and other creepy crawlies you will not want in your home or garage. Or you can cool it with an evaporative cooler or air-conditioner, both of which are a waste of your hard-earned dollars. Your garage is going to be hot in the summer!
Can you improve your home’s cooling and heating by filling concrete block walls with insulation foam? This can make a big improvement. In fact, it can improve the R-value of your walls by as much as five times. It can take your home from R3 to R11.
Should you use elastomeric paint or ceramic paint to reflect sunlight off your home. Probably not. It can cost up to three times as much as a quality exterior acrylic paint and will be costly to repair later. You cannot patch a wall that has this paint, and you will be stuck with recoating an entire wall. Focus on your attic instead.

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