The window to a zero energy home, Richmond, VA style...

When it came to window choices, there was a lot to consider, because as you increase the tightness and the insulation level of your home, the glazing makes a greater impact on energy usage. And our particular home design has a lot of windows! Looking to the Efficient Windows Collaborative (EWC) for guidance, the 2009 Energy Star standards for Virginia suggested windows with a U-factor (the rate of non-solar heat loss or gain
through a whole window assembly) of .40 and a SHGC (the Solar Heat Gain Coefficient is the fraction of incident solar radiation admitted through a window) of <.40. But our EarthCraft builder reminded us that the EnergyStar standards were going to be tightened starting in 2010, so we set out in search of better windows. The new Virginia Energy Star standards are a U-factor of .32 and a SHGC of <.40, but few suppliers had windows available reflecting the new values yet. After some creative searching, Mark found us PlyGem MW Pro Series windows with a U-factor of .29 and SHGC of .25 for only $400 more than 2009 rated windows. These are vinyl clad PVC construction, 20 year, double pane, argon gas-filled, low-E glass windows with a Warm Edge technology ( the Warm Edge glass spacer system reduces thermal transfer around the glass perimeter by utilizing a unique U-shaped channel to separate glass panes and interrupt the natural flow of heat to cold). Hopefully the added insulation they provide will reduce the load on our geothermal HVAC system. We are hoping that the lower SHGC will work well, as we have a lot of southeast facing glazing on the back of our house, which because of solar sighting, has little shade in the summer, making excess heat gain in hot muggy Virginia a potential problem. Oh, and that door you see there, that is the Therma-Tru Classic-Craft® Mahogany(waiting to be stained) fiberglass front door, which is also EnergyStar rated. Have to have all the portals covered...

Solar PV arrives at the Virginia zero energy home!

Every zero energy home needs a renewable power source and ours consists of 20 Schuco SPV 210 panels supplied by Dereck McAvoy of Midsouth Building Supply. These monocrystalline panels are some of the more efficient ones available, rated at PTC/STC 91.5%, indicating that they in effect, under real world conditions, produce very close to their advertised power rating. They are warrantied to produce at least 80% of their initial output for 25 years. They are on the List of Eligible SB1 Guidelines CompliantPhotovoltaic Modules for the Go Solar California program, one of the longest established and most respected state solar programs. They were installed on the back face of the south facing garage by SunFlower Solar and connected to a SMA Inverter SB 5000us attached to the inside wall of the garage, that wirelessly sends production data to my laptop. The inverter, warrantied for 10 years, converts the DC output to AC and feeds it to the house with the excess going back into the Virginia Power grid with the help of a grid-tie connection to their net metering program. This program allows two way metering, so that excess power can flow into the grid, and needed power (ie. at night) can be drawn out. The arithmetic sum is carried over a 12 month period. If you produce excess power it can be carried forward; if you fall short, it can be subtracted from that sum (or you pay a bill). Any excess that is not used in a 12 month period is donated to the grid, and you get warm fuzzy feelings for your kindness to humanity. All of this now sounds very simple, and the panels look neat and clean. Let me tell you, pulling this together was not simple, neat or clean. It took many hours of active research, several false starts, a motivated, thoughtful builder, and several solar resource experts to make this happen. More on this later.

ZEH, SIS, and other energy-friendly acronyms to know

The envelope of the house is rapidly developing, so its time to highlight a few key products. The house will have an exterior sheathing of a new product from Dow, Styrofoam SIS (Structural Insulated Sheathing). Winner of the 2009 Green Product Awards from Building Products Magazine, STYROFOAM SIS™ Structural Insulated Sheathing from Dow combines a structural layer, a moisture barrier, and foam insulation, providing R-values of 3.0 at ½ inch or 5.5 at 1 inch. Made of up to 80 percent post-consumer recycled content by weight, STYROFOAM SIS™ Brand Structural Insulated Sheathing is ENERGY STAR-qualified. And, at one-third the weight of OSB†, it is easier to handle and quicker to install. One judge summed up the products benefits as, "This appears to be an excellent product, providing wall bracing, energy performance, and the potential for weatherization all in one. The labor savings alone is huge." Our builder chose to use the 1/2 inch product, after an analysis revealed relatively little energy gain for the thicker product in our build (rule of diminishing returns). The panels are nailed or stapled in place to the outside of the studs and the seams are taped with WEATHERMATE™ Construction Tape (2-7/8" wide) .

WEATHERMATE Construction
Tape is pliable, ensuring a tight
seal, even at extremely low

temperatures. The oriented
polypropylene backing is
formulated with a UV-treated
film to help resist degradation
from exposure to sunlight.

The garage is not insulated, but covered with WEATHERMATE™ Plus – Housewrap to serve as an air and moisture barrier. It is significantly superior in water resistance, air porosity, vapor permeability and tear resistance than the more commonly used Tyvek. It also possesses prolonged UV ray resistance, allowing it to be exposed up to 120 days before significantly degrading (hopefully our garage will not test that limit).

ZEH Virginia, its all in the little things

Building a green ZEH is not one big thing, but a series of many little things. Our builder is using AdvanTech subflooring, a product offered by Huber with a 50 year guarantee that shows significant improvement over both OSB and plywood in stiffness, strength and water resistance, while using no added formaldehyde and meeting the Sustainable Forestry Initiative (SFI) Standard. This produces stiffer, quieter floors while minimizing outgassing. The piece of light blue material you see sticking out from the block in the lower picture is a foam gasket that serves as an air sealing measure along the uneven block and brick. It also is a moisture break to keep water from migrating to the wood from the foundation. The aim of maintaining an extremely tight "envelope" with respect air and moisture infiltration is a guiding principle that directs innumerable building product choices and practices when constructing a zero energy home. Mark, our builder, is shooting for the lowest HERS rating house in Virginia, so each of these decisions is made with efficiency and best practice in mind.

ZEH design blueprint

Where did the design of this ZEH house come from? Good question. A lot of tiresome searchs on the internet uncovered a few rare nuggets. The first and in many ways the most fruitful was the Zero Energy Home section of Toolbase Services: the Home Building Industry's Technical Information Resource. This site has a wonderful article titled Seven Steps to a ZEH that is the closest thing to a ZEH "blueprint" out there. Links to scientifically monitored zero energy homes, like the Tuscon's Zero Energy Home were invaluable not just for the data they included, but the encouragement they provided that this is indeed a practical, achievable goal. Given we became interested in the combination of solar PV and geothermal HVAC after tossing around ideas with our builder, Mark Waring, finding the series of articles titled Energy efficiency, SIPS, geothermal, and solar PV used in near zero-energy house was like striking gold, as it documented and evaluated a series of homes using this exact combination. In looking for books on the topic, the pickings were slim. Ed Begley's Guide to Sustainable Living served as good primer for general energy-efficiency ideas, while Got Sun? Go Solar by Ewing and Pratt was a practical, content-rich guide to utilizing solar PV as part of a ZEH effort. The Renewable Energy Handbook, Revised Edition by Kemp offered a broader exploration of alternative energy alternatives. Toward a Zero Energy Home by Johnston & Gibson is a very recent release whose greatest value may be its descriptive "Case Studies" of 13 near ZEHs. Two magazines that offered some help were Solar Today Magazine and HomePower Magazine, the former focused on solar power, but from a wide ranging perspective, while the latter is more focused on real world applications of renewable energy, including solar, and yielded needed product information. In the end, working with our builder who was already experienced in building energy efficient homes, pulling ideas from a variety of sources, and considering and ruling out some promising but impractical combinations, we embarked on an informed leap of faith. Time will tell how much of a leap, and we work with our builder on a weekly basis to continue to hone and fine tune the design, in search of that elusive "zero."