The green building sector is getting ready for the Jan. 1, 2019 deadline for all HERS raters to use an amendment that puts smaller homes on a level playing field.
As was previously reported, RESNET’s index adjustment factor was developed because larger homes were found to have 20% better (lower) HERS scores for the same energy measure.
As the floor area or number of home stories increased, the index went down because of a mathematical quirk in the way the formula was written.
“We found that if you keep the material properties the same — such as thermal efficiency, walls, ceilings and floors — and just increase the floor area of the home, larger homes did better on the HERS index,” said Philip Fairey, deputy director of the Florida Solar Energy Center. “This amendment evens out the difference between large and small homes constructed with the same building envelope. It makes the two homes behave more alike.”
In regard to floor area, EnergyGauge USA found that incorporating the index adjustment factor reduced HERS score variations from 10.8 points to 2 points.
Fairey sees this amendment as a much-needed mechanism to ensure parity in the HERS rating system. “I don’t think we should have a system that advantages homes based on home size,” he said.
The timing of the amendment coincides with the overall decrease in new home size. New homes had been decreasing in size over the last two years as builders added more entry-level homes for millennials and other first-time home buyers. Although new single-family home size increased at the beginning of 2018, NAHB economists expect it to drop again as additional moderately priced homes are constructed for market newcomers.
As home size decreases, home buyer preferences for green building is holding strong. NAHB research has shown that energy-efficient strategies, including ENERGY STAR-certified appliances and windows and above-code insulation, are on “the most wanted” list of home features.
With the amendment in place, the HERS rating system will no longer disadvantage the many environmentally conscious home buyers who want or need to buy a small home — and the builders who construct these houses.
“A lower HERS score means lower energy use, which will appeal to buyers,” said Fairey. “Builders marketing homes with the HERS index will appreciate this effort to keep small homes on equal ground.”