Different Shades of Green

Green Leaf of a Bio Plant in Nature

Green Leaf of a Bio Plant in Nature (Photo credit: epSos.de)

The catch word these days in home construction and renovation is “energy-efficiency”.   A kitchen update may include the replacement of old appliances for “energy-efficient” ones. Full gut jobs of older homes allow the addition of wall insulation and better overall “energy-efficiency.”  However, one edge new construction has over renovation is the option to use today’s technology from the ground up. In Pittsburgh, nearly all “green” urban infill projects are highlighting the energy efficiency of their homes and informing potential buyers of future cost-savings in energy bills. There is definitely an appeal to putting today’s technology into today’s house, not fitting it somehow into yesterday’s.

What the consumer needs to understand, however, is that the “energy-efficiency” of any home is relative.  It is relative to the measure being used as the standard.  The exact same house placed in San Diego would be more energy-efficient than if it were placed in Pittsburgh.  Why?  Because the heating and cooling needs in San Diego are minimal, it has nothing to do with the construction of the house.  Therefore, one needs to understand what standard is being used in order to determine if the label “energy-efficient” is even meaningful.

Fortunately, there are government standard ratings and also impartial third-party ratings that have established the current standard.  Getting a home certified according to these standards gives the consumer a benchmark to decide if that level of “energy efficiency” is green enough for them.  For residential home construction, two popular standards are the Energy Star ratings (http://www.energystar.gov/index.cfm?c=home.index)  and the HERS Index (http://www.resnet.us/ ).  Others, which I won’t discuss, include Passive House construction standards and the LEED ratings.

How a house earns the Energy Star label  (Note: we are not talking about appliances, but the actual whole entire house) or how a HERS Index score is calculated is complicated.  How they calculate the cost-savings in dollars and cents is even more complicated.  The real question for me, however, is not the “how”.  It’s when they say an Energy Star certified home is 15% more efficient, my question is “15% more efficient than what??”

Look for this logo when considering your new r...

Look for this logo when considering your new roofing materials (Photo credit: Wikipedia)

The simple answer is that it’s 15% more efficient than an imaginary home meeting current minimum code.  Yes, the “standard” is an imaginary home.   It is an imaginary home in the same climate, of the same size which was built according to current building energy code.  Therefore a “green” home goes above and beyond minimum building code requirements and should be a cut above the standard.  On the HERS Index, this standard is called a reference home and gets a score of 100.  A house with a HERS Index of 85, for example, is 15% more energy-efficient than the reference home.  A house with a HERS Index of 130 is 30% less efficient than the reference home.  Note that building energy codes change over time as technology advances, so what is considered “efficient” now may be the new standard in 10 years.

What’s interesting about this year is that Energy Star has changed its requirements.  In the past, a house had to have a HERS Index Score of 85 or lower to earn the label (among a checklist of other things).  Now, it has to have the same HERS Index Score as the Energy Star Reference house (plus the checklist of other things).  However, the HERS reference house and the Energy Star reference house are not the same.  The Energy Star reference house is an imaginary house of the same size and climatal area as the new home, but it is built to meet the specific Energy Star checklist of requirements.  This imaginary reference house then goes through the HERS rating process and earns a score.  It’s probably safe to assume that the score will be at minimum an 85, if not better.  Look for new construction advertised as “green” as having both an Energy Star label and a HERS Index Score.

Photo credit:  archiadesign.com

So how does this information help me?  Personally, I love the HERS Index.  While the Energy Star labeled homes vary on the HERS Index, probably between 60-85, the HERS Index gives me one number that tells me how much net energy the house is expected to consume.  There are limitations to relying on the label and/or the index; one obvious one that comes to mind is they don’t take into account consumer habits.   I have a bad one of always leaving the towel warmer on.  But they do provide a very good frame of reference.


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