Wes Golomb and Bob Irving
Our society’s well-being is dependent upon our ability to move from a fossil-fuel economy to an economy based on sustainable energy. A path to this goal can be described as the “three-legged stool” approach.
The first leg of the stool is efficiency. In short this means using the minimal amount of energy needed to accomplish a task. Using light bulbs, for example, you could use an incandescent or compact fluorescent bulb, but the most efficient lighting would be a LED. Each energy- consuming device should be analyzed similarly to determine the most efficient way of accomplishing the desired task.
The second leg of the stool is electrification. This means the conversion of fossil fuel combustion engines or heating units to electricity. In general, such a conversion cuts the amount of energy required for a task by about one-third.
The third leg of the stool is the generation of electricity by sustainable means such as solar, wind, and hydroelectric.
On a macro scale, this three-legged stool approach is the blueprint for our society’s path to decarbonization. On a micro scale, it is the exact recipe for building a net-zero home.
The net-zero home we’re going to focus on is a home that RH Irving Homebuilders built in Barrington, NH which uses the three-legged stool strategy described above.
Lessa Brill and John Wallace raised their children in Barrington, NH. They wanted to downsize and remain in the community. An energy-efficient home was high on their priorities list, but, after an exhaustive search, they could not find such a home for sale in their community. This was the motivation to build a home.
In a house, making the envelope as tight as possible is a primary strategy for maximizing efficiency; appropriate types and amounts of insulation and high efficiency appliances are also key components.
The Wallace Brill home is a post and beam construction. It is built on a slab and has no attic or basement. A rubber EDPM gasket was used to air-seal the sill, and six inches of expanded polystyrene (R24) insulates the concrete floor. All seams on the exterior are taped. The house tested at less than one air change per hour, a very respectable number. However, the sill remains a source of some air leakage.
Since building this house RH Irving Homebuilders is using a different technique. After the foundation is poured, an ice and water shield is installed onto the inside of the foundation walls. It is then adhered to the top of the foundation and after the walls are built, it is attached to the outside of the wooden wall. This way no air can penetrate the sill.
The house has double two-by-four walls with a three-inch gap (ten inches total) filled with cellulose insulation. The double walls minimize thermal bridging. The windows are triple pane.
The construction of the timber framed roof presented an interesting challenge. It needed to be air sealed, super-insulated and thermal bridging minimized without using foam insulation. The challenge was to satisfy all of these requirements and produce a finished ceiling of two-by-six spruce.
The spruce sits on top of the beams, so the builders had to build from the bottom up. A peel-and-stick membrane was applied to the spruce ceiling and serves as part of the ceiling air barrier, above which sit sixteen TJI’s (Trus Joist I-Joist, engineered floor joists and rafters made from wood chips). This met all the structural requirements.
The TJI bays were filled with R-60 batts of rock wool insulation thencovered with half-inch oriented strandboard (OSB) sheathing. The roof is strapped with two-by-fours above the TJIs allowing the needed air space to vent any moisture so as to keep it from accumulating. The roof assembly was then covered with half-inch Advantech, a type of high-density sheathing that looks like an OSB but is water-resistant. The Advantech was covered by a roofing membrane fabric and lastly, a low maintenance standing seam metal roof.
Like all tight houses, the Wallace-Brill home needs heat recovery ventilation (HRV). Instead of using a ducted central system, a Lunos through-the-wall system was used. This system uses pairs of circular vents with ceramic cores which absorb and release heat and are installed in synchronized pairs for balanced ventilation. One unit supplies incoming warmed air, the other exhausts air which loses heat to the ceramic core, and they switch direction at one-minute intervals. There is some noise associated with the Lunos which is noticeable and sometimes annoying.
The home satisfies the first leg of the stool, efficiency, by airtight construction, and high levels of insulation Additionally, it minimizes electrical demand with LED lighting, efficient kitchen appliances such as an induction cook stove, and heat pumps to heat, cool and dehumidify.
The second leg of the stool, electrification, is accomplished by using an induction cook stove, and heat pumps which efficiently heat and cool with no combustion. John and Lessa augment the heat pumps with wood heat.
The third leg of the stool, sustainable power generation, is accomplished with 6kW of rooftop solar installed by 603 Solar. Last year they spent $150.00 on electricity and burned less than two cords of wood.
Wes Golomb, is a long-time clean energy and climate advocate from Deerfield, NH. Bob Irving is the owner of RH Irving Home Builders, specializing in high performance building practices since 1972.
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