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.”