Ask the Expert: Is masonry insulation worth the money and effort?

By Ken Sheinkopf

Q: I have been considering masonry insulation on my future new home. I understand that insulation on the walls will save a lot of energy. Do you think it is worth the $1,000 or so it will cost to have it installed?

A: The general answer to a question about the benefits of wall insulation is that it depends on the climate where the house is located. It is probably a very worthwhile investment in a climate where a lot of heating is used, but research has found minimal results in a cooling-dominated climate. Walls typically account for only about 10 percent of the total cooling load in the home, meaning there isn't that much potential for significant cost savings.

In 1994, researchers at the Florida Solar Energy Center put exterior insulation on two residential homes in Central Florida. The houses were instrumented to collect electrical power-use data and meteorological data. The initial phase of the study was conducted during the first half of summer while the homes were in their standard configuration. The data collection then continued for the balance of the summer after exterior insulation had been installed. Researchers used three different methods (matched days, long-term periods, and a simulation model) to analyze the data. The indicated summer season savings ranged from 9 percent to 14 percent of air-conditioning use at one of the homes, with a negative savings of about 5 percent at the other. The average reductions in cooling energy use during peak periods were modest at the first home and negligible at the second one.

Analysis of individual matched days indicated that the differing savings at the two sites might be largely explained by the different thermostat settings maintained inside the two homes. Site 1, which maintained an average interior temperature of approximately 73 °F, had an energy savings, while Site 2, with a 79 °F set point, did not.

The simulation analysis of a prototype home conducted by the researchers confirmed the important role that the difference between interior and exterior air temperature plays in the effectiveness of insulation on exterior masonry walls in reducing cooling needs.

The researchers concluded that appreciable reduction in cooling AC use in Florida homes will most likely be realized only in cases with low cooling thermostat settings. While aesthetically pleasing to the homeowners, the low energy savings clearly make such an improvement non-cost effective from an energy-efficiency standpoint.

Keep in mind that this study was conducted in a climate with heavy cooling and minimal heating use during the year. The results may be very different in climates that use much more heat.
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From the editor:
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Editor's Note: Ken Sheinkopf is Associate Director of the Florida Solar Energy Center. Write to him at 1679 Clearlake Road, Cocoa, FL 32922, or e-mail Sheinkopf@fsec.ucf.edu

Mr. Sheinkopf cannot answer every question personally. Check back here at www.crest.org to see if he's already answered your question.

REPP does not endorse products and this is not to serve as a scientific or comprehensive analysis of any product.