November/December 2008 Issue

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How competing in a Massachusetts homebuilding competition reshaped one builder’s approach to affordable, high-performance homes.

Text and photos by R. Carter Scott


My firm has been building renewable energy-powered houses according to sustainable practices for years. In 2006, we initiated the Coppersmith Way development in Townsend, Mass., with the goal of building environmentally friendly, price-competitive solar homes — an experience I detailed in these pages (see “Built Green at Coppersmith Way,” September/October 2007 issue). So this spring, when the state’s investor-owned utilities announced the Zero Energy Challenge, we were raring to compete.

As sponsors of the Massachusetts New Homes with Energy Star program, the utilities developed the competition to “encourage builders to design and construct homes [using] considerably less energy than homes built with traditional residential practices, products and technologies.” ICF International, the program administrator, solicited submittals from homebuilders and homeowners and chose six builders who could plan and deliver a built home with a Home Energy Rating System (HERS) Index below 35 before December 2009. For comparison, a home must earn a HERS Index of no more than 85 to rate as an Energy Star home. At the end of the competition, the three homes with the lowest HERS Indexes will split $50,000 in prize money. The grand prize winner will receive $25,000, the first runner-up $15,000, and the second runner-up will win $10,000. It was an ingenious way to get more firms thinking about zero energy design, at a contained and predetermined cost for the sponsors. My company, Transformations Inc., was chosen as one of the six builders.

What constitutes a zero-energy home? Zero net energy means the home produces as much energy as it uses, so the owner purchases no energy on an annual basis.

It’s no small design challenge. Not only must you be scrupulous about how you design the house to use energy, but you also need a way to make that energy. Zero-energy homes usually include a photovoltaic (PV) or wind energy system, to generate electricity on-site. When the sun is shining or the wind is blowing and the home is using little electricity, the PV- or wind-generated electricity is fed to the electric grid, running the home’s electric meter backwards. At night, when the sun isn’t shining, the home draws this “stored” electricity from the grid, running the meter forward. If all goes well, at the end of the year the electric meter is in the same place it started.

Our first task was to produce a set of plans for a zero-energy home — and fast, because they had to be submitted within 60 days. I started with a home design drawn up by my architect, Ben Nickerson, who was inspired by an existing farmhouse. We called it the Needham. Based on Ben’s design, my Energy Star rater, GDS Associates of Manchester, N.H., had rated the home with a HERS Index of 31.

The HERS system assigns an energy use index of 100 to a comparable reference home built to the International Energy Conservation Code 2006 (IECC 2006). To qualify as an Energy Star home, a HERS Index of 85 or less is required, meaning the home must use at least 15 percent less energy than the IECC 2006 code home. So we were starting with a very efficient home, since the HERS index of 31 means the home was projected to use 69 percent less energy than a comparable home built to the IECC 2006 code.

The design called for a three-bedroom, 1,232-square-foot (114-square-meter) house with the master bedroom on the first floor and two additional bedrooms upstairs. The standard construction we used at the time for our affordable housing was 2x6-inch (5x10-cm) walls filled with high-density cellulose, using advanced framing techniques such as 24-inch (0.6-meter) on-center framing, two-stud corners, and headers designed for their loads only; an inch of rigid foam on the outside for a thermal break; careful attention to air sealing; low-E windows filled with argon gas; an efficient combination boiler for water and baseboard heating; and a 3.6-kilowatt PV system on the roof.

Brian Adams of GDS took on the task of rating our different construction options, to see how we might make the house even more efficient. We must have done 20 iterations trying different scenarios: a 5.04-kW PV system, triple-pane windows filled with krypton gas, extra thermal mass, more windows on the south, more energy-efficient appliances and super insulation of the walls/attic/basement. These options helped us get down to an index of 18 with combinations of successful upgrades.

Finally I received an email from Brian: “We are at 0!” To get there, he had modeled the house with a heat-recovery ventilator (HRV) and a high-end solar water-heating panel system with radiant floor heating.

With a sale price cap of $195,200 for this affordable, deed-restricted home to be built in our Coppersmith Way development, I needed to keep the costs in line. Mike Duclos of Energy Efficiency Associates in Stow, Mass., went over the house design and HERS model with a fine-toothed comb and soon turned up a problem. Mike found that despite a claimed U-value of 0.10 (R-10) for the triple-glazed window we planned to use, the manufacturer’s calculation was based on the center of the glass rather than the whole window, as specified in the HERS manual. Our zero-energy computation was blown, and we went back to the drawing board.

I had been studying the “Getting to Zero” presentation that Energysmiths principal Marc Rosenbaum made at a building conference in Boston. In it, he modeled nine hypothetical plans and, it was apparent that a super-insulated house with a PV system on the roof and an inexpensive heating system was the way to go. Based on this knowledge, we went to a super-insulated shell with PV and solar water heating to get to zero energy.  Rosenbaum also consulted on our home’s energy systems, rounding out our Dream Team of energy-efficiency experts.

My insulation contractor, Anthony Cuzzi of Mor-Tite Insulation, priced out various options for insulation. There are pony walls (2-foot by 3-inch knee walls) in the second floor of this house design, which would tend to have air leakages. To minimize this air infiltration, we went with a “hot roof” — an unvented, super-insulated roof. Massachusetts code requires 40 percent of a hot roof to be made up of foam if you use high-density cellulose. So we have 5 inches (12 cm) of high-density polyurethane foam (HDF) and 13 inches (0.33 m) of high-density cellulose all along the slope of the second-floor roof rafters. We used 2x12s and a 2x4s held off by 3 inches for a thermal break separation. That resulted in an R-value of 75 in the cavity wall of the roof slopes.

For the walls, we started with a 2x4 outside wall. We added a second 2x4 wall for a total depth of 12 inches. We filled 3 inches with HDF and 9 inches with cellulose, resulting in an R-value of 49 for the cavity.

The basement ceiling serves as the lower boundary of the thermal envelope. If we insulated the basement walls and left the basement ceiling uninsulated, we would have been penalized 2 HERS Index points. So we installed 3 inches of HDF and a layer of R-30 fiberglass batts in the basement ceiling.

Super-insulation of the house came in at $14,000. Our standard insulation techniques would have cost $8,030, so the marginal cost was about $6,000. We upgraded our Paradigm windows from the thermo-pane, argon-filled low-E model we usually use to Paradigm’s triple-pane model with low-E and krypton gas (paradigmwindows.com). That increased the cost of the windows and doors from $4,342 to $5,031, for an increased marginal cost of $689.

The cost of labor and materials for the extra 2x4 wall was $900. But we achieved overall savings with the double-wall construction. We flared out the walls with blue-board and plaster at the window locations for better daylighting. As a result, we didn’t need to trim our windows, saving us $250 in carpentry labor and $1,078 in wood window-trim materials. We also avoided installing an inch of rigid foam on the outside, saving $550 in labor and $1,708 in materials.

Since our heating load is very small due to the use of super-insulation, we don’t need an expensive heating and air conditioning system. We looked into mini-split-system air-source heat pumps. Relying on this small, high-efficiency system helped offset our investment in super-insulation and windows, while making the most of the PV-generated electricity. Our peak heating load on the house is around 10,500 Btu — so low that we can heat the home with the equivalent of two 1,500-watt hair dryers and an 80-watt light bulb! The math: 1,000 watts equals 3,413 Btu of energy; so 10,500/3,413 equals 3.076 kilowatts (kW), or 3,076 watts, of heat required at design temperature.

We selected a Mitsubishi Mr. Slim split-ductless air-source heat pump (mrslim.com). We installed a 12,000-Btu head downstairs and a 9,000-Btu head in the upstairs hall. That provided both efficient heating (HSPF of 10) and air conditioning (SEER of 16). The cost of the system was $5,250 installed. The affordable heating system we previously used in our homes was $6,800 and included no air conditioning. The typical heating and air conditioning system would cost about $14,000 for this size home. So our investment in the super-insulation and high-performance windows was more than offset by the reduced heating cost and the value of the air conditioning system.

I noticed we were using a lot of energy to mechanically ventilate the house. Mike researched heat-recovery ventilators and identified a good fit for us in the Lifebreath 155 ECM Energy Recovery Ventilator (lifebreath.com). It uses just a tiny amount of electricity to constantly circulate air into and out of the building. We extract about 64 percent of the sensible heat from inside air and transfer it to the incoming unconditioned air. That incoming fresh air is vented near our mini-split system for immediate conditioning.

Once we had whittled the home’s energy requirements to a bare minimum, it was time to focus on the on-site solar energy systems.

For the solar electric-generating system, we went with 30 Spruce Line 190-watt PV panels from Evergreen Solar to create a 5.7-kW system (evergreensolar.com). We arranged them in three strings into a Fronius IG 5100 inverter (fronius-usa.com). The installed cost of the PV system was about $33,000. After a rebate of $25,200 from the Massachusetts Technology Collaborative, the final cost to my company will amount to $7,800. The homeowners will receive a $2,000 federal tax rebate and a $1,000 state tax rebate.

Since hot water accounts for 20 to 40 percent of a typical home’s energy requirement, producing it cost effectively is important. We chose SunDrum Solar’s innovative solar water-heating system (sundrumsolar.com). The SunDrum collectors, which fit into the underside of the PV panels, remove heat from the PV collectors and use it to heat household water. Drawing heat from the PV also cools the crystalline cells, making the PV system more efficient.

By using nine SunDrum collectors, we provide solar heating for about 90 percent of the two-person household’s hot water needs. We also are gaining 10 percent in efficiency for the SunDrum-mounted PV panels. Mike Intrieri from SunDrum Solar very graciously donated the panels and required connections for this competition. The next nine-panel system we install, including the cost of installation on the roof, plumbing connections and a hot water tank, is expected to cost around $6,300.

Based on our experience with the zero-energy Needham home, we have two more zero-energy market-rate homes on the drawing board for the Coppersmith Way development. The first is an 1,818-square-foot (169-square-meter), two-story version of the Needham plans, called the Farmhouse. It is already under contract for $359,900. The second is a 2,100-square-foot (195-square-meter) Greek revival plan priced at $389,900.

The Zero Energy Challenge has inspired other projects for the company. In September we began acquiring land for an eco-village community to be developed on the Massachusetts north shore. Plans include ZEHs, sustainable building materials and edible landscaping in a clustered village setting. In Harvard, Mass., we are in the permitting stage with a 24-unit mixed-income project. The intention is to reduce the energy requirements for the homes by 90 to 100 percent, averaged across the whole development. We closed on a four-lot conservation development in Princeton, Mass., where we have a zero-energy saltbox home proceeding to the build-out stage.

The Zero Energy Challenge is also attracting attention beyond our commonwealth. In June, the Planet Green television network’s “Renovation Nation” show filmed construction of our Needham zero-energy home. Host Steve Thomas interviewed our homebuyers, Mike Intrieri and me. It was a blast. The crew obtained footage from inside and outside the house, of the SunDrum water-heating installation and the air-source heat pump mini-split system, and of the new homeowners blowing cellulose insulation into the walls. The episode should appear this fall.

The Needham is currently in the final certification process with our local utility. We are on track to receive our “0” HERS Index. The remaining five homes entered in the Zero Energy Challenge need to be built out before a winner is announced sometime next year. At the house plan submission stage of the competition, we were in first place, with the only 0 HERS Index.  The other homes came in at 6, 18, 19, 20 and 30. 

The Needham’s new owners love their zero-energy home. After purchasing it July 25, they used the air conditioning system only once this summer, for 20 minutes, to test it.  Participating in the Challenge has revolutionized the way we approach low-energy homebuilding. It has been incredibly satisfying to design and build a home that will essentially emit no greenhouse gases and cost the homeowner next to nothing for their heating, air conditioning and electrical usage. If we can build an affordable zero-energy home with adequate heating through the harsh New England winters, can a national movement to ZEHs be far behind?

R. Carter Scott is president of Transformations Inc. (transformations-inc.us), a sustainable development and building company is Townsend, Mass. He can be reached by e-mail or phone: 978.597.0542.

Online Extras —

• Lifebreath 155 ECM Energy Recovery Ventilator provides low-energy ventilation: $2,300 installed
• Hybrid photovoltaic-solar water-heating system covers most of the home’s energy needs on an annual basis
• 5.7-kilowatt photovoltaic system comprises Evergreen Solar’s Spruce Line panels: $7,800 after Mass. Tech. Collaborative incentive (before federal and state tax credits)
• 9 SunDrum Solar LLC collectors use photovoltaic system’s heat to produce domestic hot water: valued at $6,300 installed
• Completed and purchased, for $195,200, in July

Builder
R. Carter Scott, Transformations, Inc.
transformations-inc.us

Architect
Ben Nickerson
978.369.7020

Home Energy Rating System Experts
Brian Adams, GDS Associates
gdsassociates.com

Mike Duclos, Energy Efficiency Associates
Stow, MA 01775
978-897-5124, This e-mail address is being protected from spambots. You need JavaScript enabled to view it

Energy Systems Consultant
Marc Rosenbaum, P.E., Energysmiths
energysmiths.com

Insulation
Anthony Cuzzi, Mor-Tite Insulation
mor-tite.com