“All healing is essentially the release from fear.”- A Course in Miracles
If you’ve been my reading previous posts you know that I believe that “sustainable” in the context of “home”, can only mean “net zero” or “energy zero” construction. What that means in practical terms, is that the thermodynamics of the building design (insulation levels, window performance, tightness, solar gain, etc.) must be good enough to allow the reasonable application renewable resources like solar or wind power to render the building a net zero energy consumer. By net zero, I mean that the home may have PV system that uses the grid as a storage device and although it may draw power from grid at times, on average the home delivers at least as much power to grid as it consumes.
The HERS Index is a good metric to help quantify the design performance required to meet this standard. I my opinion, the design of the home prior to the application of renewables, to be “good enough”, must have a HERS Index score of 25 or better to be “net zero ready”.
Unfortunately of the million or so homes built every year, my guess is that less than a thousand (perhaps less than 100) meet this standard. These are the hardy souls that build Earth Ships or are determined enough to find the few professionals who know how it’s done, regardless of the climate or any bias toward a specific building system. But in the long run it’s not the new homes that will be the challenge, it’s the over 100 million existing homes that grace the HERS Index scale from 130 to 150+. Some of these will of course be lost causes, economically not worth the effort, however the vast majority can be reasonably retrofitted, if not to 25 threshold, at least to below 50.
Stay tuned, I’ll be writing a series of “Zero Energy Home” posts that will cover the thermodynamic basics and strategies for retrofitting our existing housing stock.