Green Defined Through HERS Scores

Paul Eldrenkamp

With all the hype about "Green Building" going around, it is hard to really understand who is making a difference and who is just riding the trend.

At Byggmeister, we use HERS ratings to help us plan each major project. "HERS" stands for Home Energy Rating System, and it's a nationally recognized metric for "scoring" individual homes on their energy usage. You can get detailed information about HERS ratings at www.natresnet.org. Briefly, however, a HERS score of 100 means the house meets the basic building code requirements for energy usage. A score of 85 means the house performs 15% better than code and thus meets Energy Star standards in our climate zone; a score of 0 would mean that it was a net zero energy house; a score of 150 would mean it was 50% worse than code. So lower is better, higher is worse. It's possible to get negative score, which means that the house is a net energy producer (that is, through on-site generation by means of a photovoltaic system, the house produces more energy than it consumes on an annualized basis), though this is rare, needless to say.

HERS scores are generated by inputting lots of data about your house into an energy modeling software program called REMRate. It can take several hours to gather and input the information. On most of our major projects, we start off by calculating the HERS number for the existing house. Most of the homes we work on score in the range of 150 to 200, pre-project. We use the REMRate software during the planning process to run "what-if" scenarios to help us determine the optimum way to reach a certain result. For instance, if the goal is to achieve a score of 75, we can develop several different "packages" of various window improvements, insulation upgrades, and boiler choices that will get us there.

We've had some real successes using HERS as a planning tool. Some examples include a Victorian in Cambridgeport where we brought the HERS index from 186 down to 87; a Cape in Newton that went from about 140 down to 70; and an 1889 Queen Anne where we went from an index of nearly 200 down to 89 — almost Energy Star standard! As we use the software more and more and continue to develop strategies for significant improvements, and as energy costs continue to climb and homeowners give us more latitude with regard to the percent of the budget allocated to energy improvements, we anticipate that the HERS numbers we achieve will only get lower and lower.

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