Energy Star

The first priority for anyone building a green home is energy efficiency! Almost anything else you do to "green" your home pales by comparison to the impact you can have with energy efficiency. One of the measures of how we're doing with our energy design is our HERS rating. The Home Energy Rating System (HERS) is a numerical reference number that compares a home's energy design to a "reference" home that rates 100. To gain an "Energy Star" certification, a home must beat the reference standard by at least 15%. That is, when our home's design is audited, we've got to score an 85 or less.

We hired Bruce Glanville of the Knox Housing Partnership to rate our home. The image here is Bruce conducting a "Duct blaster" test to determine how well our HV/AC duct system is sealed. It's a measure of how much of the air conditioning and/or heat leaks out into the unconditioned attic. The HERS rating also looks at the insulation system, the heating system selection, the amout of glass and its emissivity (E-factor), the solar gain, and the efficiency of appliances. At the preliminary rating estimate in November we scored a 62. That's a darn efficient design! Sweet! This preliminary rating was also very timely.
We've agonized a bit lately over the insulation system to choose. Our spec has called for open cell foam insulation throughout, but that is a very expensive choice. Our builder has proposed a hybrid "flash and batt" system where we use a thin layer of foam to seal the entire building envelope and provide a bit of insulation (R= 7), but then fill the rest of the wall cavity and attic with conventional fiberglas batts and blown cellulose. The flash and batt proposal will save us over 60% of the insulation cost. It turns out... the full foam system, while exotic and fun to talk about, doesn't really gain us any energy efficiency to speak of. Our projected HERS rating doesn't change at all with the more expensive insulation! Well... suddenly, the decision was made easy. Flash and batt started the next day at a savings of almost $14,000!

Once I find my camera, I'll post a few images of the insulation system being installed. It's pretty cool.

Structural Insulated Sheathing (SIS)

Once I learned that Dow Chemical (my old stomping ground for a few years) had last year reformulated Styrofoam to reduce the Global Warming Potential (GWP) of its blowing agent, my appreciation for the newer building products from Dow really came around. One other recent decision that was made easy has to do with the Sheathing we used.
Traditional construction around East TN uses OSB (Oriented Strand Boasd - basically, particle board) sheathing and an overlay vapor barrier of Tyvek house wrap. You've all seen these houses. They look like a house wrapped in white paper until the outside siding is later added. (One house being built near our rental still has only the Tyvek house wrap after over a year... I'm guessing they ran out of money when the wheels came of our economy). Tyvek makes a good vapor barrier and has been a staple of the building industry for years. Our specification for this house even calls for a conventional house wrap. Rick Hessick of BR2, our builder, suggested we look at SIS and with my new-found appreciation for styrofoam, we looked closely. It's a great idea! SIS replaces the OSB, and the tyvek. PLUS, it's got a better vapor barrier performance
because it can be sealed better AND it's got the insulating properties of 1/2" of styrofoam. Since we already planned to use foam for our insulation system, this product just adds to the R-value in our wall system. To top it off.... it's a real pretty blue :)