Is anyone aware of HERS tracking 5 years or more after new construction? I am looking for a study that may provide how valid the HERS rating might be 5 years or more after new construction. Comparing the original HERS Rating to one later assuming no changes have been made to the house would provide credibility of the Index after new construction. A representative of Fannie Mae questioned using the HERS Index after new construction. It is hard to believe this type of tracking is not being done somewhere to give answers to the secondary market and public.
If changes to the structure are made or maintenance is not as envisioned, it would explain a difference. Any information you may have would be helpful. Including the HERS Rating in the MLS and other databases going further presents this question that begs for an answer.
I understand your point and I have no problem with the study you reference other than it does not answer the secondary mortgage market question as to prove the HERS Index is still valid 5 yrs or more out from new construction. They are looking for comparison using HERS Index at new construction and HERS Index 5 years or more out. The comment regarding the utilities is there are too many variables to consider it a reflection of how relevant the HERS Index may be 5 yrs or more out. It is a battle I am trying to overcome.
The problem you are trying to solve is reconciling the bias and (mis)perceptions of appraisers and the real estate industry with the intent of REM/Rate (HERS software) as an energy modeling tool.
As I said before, the HERS Index Score of a newly constructed house is fairly static and durable. If there are no substantial changes to the home, there is no need to keep verifying it. If the specs of the home are the same when it was constructed: No HERS change. Small variances in leakage test numbers don't move the number much either. I have personally seen this to be true on literally thousands of before-and-after HERS ratings when I was QA for a utility-sponsored energy audit and improvement program. Improvements don't move the needle as much as you think they would.
I also verify homes for LEED certification. If a home is LEED certified when constructed, does it need to be recertified every time it goes on the market? The answer is: NO. LEED certification is a stable selling feature of the home. The HERS Index SHOULD be thought of in much the same way for homes that were rated at construction.
This is why there is not much "out there" to answer your question. The vast majority of the home building industry isn't interested in spending the $$$ on validation studies because they have little monetary stake in resale value once the house is sold to the 1st home buyer.
Because the HERS index is also used by energy performance contractors as a way to validate their efforts on existing homes, there is a perception that a HERS score is a highly elastic, ever-changing metric that must be continually redone to be valid.
From all I have gathered, the appraisal industry is still behind the curve and has not yet fully come to terms with how they are going to quantify the HERS metric, and other green home features, into their assessment process.
It appears they may have to conduct some primary research to figure that out! :-)
Let me know if I can help...
The secondary mortgage market - Fannie Mae questioned the use of a HERS Index after new construction. The questions are not out of bias from the appraisal industry but out of defense from the secondary market. This came up at the Green Mortgage Appraisal Roundtable at the White Conference on March 11th. No one in the room could answer Fannie's question on reliability of the HERS Index 5 yrs out or longer.
I've sent this directly to Sandra but for those following this thread Building Science Corp. provided a link to a study regarding air tightness over time, which to me would seem the only real variable to a HERS score in a 5-10 year time frame (absent home modification) that might cause a change in a HERS score.
The only research that I know of that looked at air tightness results ten years later was done by Gary Proskiw.
Sam Rashkin also indicated that LBNL is currently doing a study on air tightness over time as well.
Thank you for your prompt reply with the link to a study that is certainly what I need. I look forward to seeing the LBNL research to add additional support for reliance on this method of testing the energy efficiency of a building. I hope more studies will be done periodically to allow us to have solid support for using this Index.
This should be done. We are working on it now.