Torcellini Residence, Eastford, Conn.

Hpb Spring2018 Zeroenergyhouse P2
Paul Torcellini
Nearly completed view of the south façade showing the sunroom windows and the overhang that shades the house in the summer and provides passive solar heat in the winter.

Appears in the Spring 2018 issue.

After 30 years of giving advice as a building science and energy-efficiency researcher, I, with my wife and three boys, had the opportunity to design and build our own house from scratch. What decisions would I make now that it was my home and my money? My wife and I also wanted to show that it was possible to design and build a zero energy house on a fixed typical new construction budget and that we could contain costs by carefully considering trade-offs between energy use, amenities, architectural considerations, aesthetics and other constraints.

It was definitely a family effort (see Family Life sidebar). We started the design process in the spring of 2014, and the house was substantially complete by early 2016. We used many conventional strategies and materials, but we also introduced a number of innovations that may not be for everyone. 

As a family, we have some unique requirements. For one thing, we raise and grow much of what we eat, and the house had to accommodate food storage and a kitchen that sees lots of use. We also homeschool our three boys, so we had to design classroom space. The goal was to build a modest house with conventional styling using conventional framing techniques that includes the amenities most would expect from a 2,500 ft2 house with a garage and a basement. 

Located in Eastford, Conn., the house sits on a relatively flat lot in a mixed hardwood/softwood forest. The only utility available at the site is grid-connected electricity, although it would be possible to bring in propane or oil if we chose to. The house was designed to be all-electric. The net-metering agreement compares the amount of energy “purchased” from the grid and “sold” back to the grid and the difference is reconciled annually. The meter connection fee is $19.25/month, and the utility charges about $0.17/kWh for purchased electricity.

Siting and Building Envelope
The 1.5 story house is designed to resemble a 1925 Arts and Crafts-style bungalow we renovated in Colorado in the early 2000s. We were drawn to this style because it reflects the conservation ethics and lends itself to an efficient, compact design that minimizes envelope area.
The walk-out basement includes a two-car garage as well as a modern root cellar for food storage. The basement is conditioned and is included in the normalized energy numbers. The back of the house faces due south and has a semiconditioned sunroom that extends the entire length of the first floor. The roof is pitched at 27º to the south and was designed to accommodate 9.4 kWdc of photovoltaic (PV) panels (Figure 1). 

The first floor has a “living hall” that includes a living room, kitchen, library (part of our homeschooling accommodation), laundry, and master bedroom. The second floor contains a large open space and a second oversized bedroom. The open space could be configured for a third bedroom, but currently serves as a hobby room. 

The 12 in. thick walls comprise a double row of studs with a thermal break between them. The fiber cement siding has a ¾ in. weep gap to separate it from the taped, air-impervious sheathing. Twelve inches of blown fiberglass fills the stud cavity, with a continuous air barrier between the insulation and the drywall. All exterior electrical outlets have gaskets to seal them to the drywall, and all wall penetrations are sealed with expanding foam. 

Blown fiberglass also fills the cavity between the 12 in. roof rafters. Perpendicular furring is used to support the plasterboard. Like the wall sheathing, the roof deck is taped. An air space provides ventilation between the roof deck and the standing-seam metal roof. 

The roof has an Energy Star-rated roof. An air gap below the metal roof provides ventilation to keep the roof system cool. Another benefit of the roof system is the ability to clip on the PV panels, which further shades the roofing structure, doesn’t require roof penetrations, and ultimately reduces summer heat gain to the roof and improves interior comfort. A minimum of R-50 insulation was used on all exterior walls and the roof structure, and portions of the roof exceeded R-80.


Construction photo showing the north and west façades of the house.

Paul Torcellini


The windows are double hung, which typically increases infiltration rates. Although not the perfect energy-efficiency option, we chose them because they fit the architectural style of the house. Unlike casements, they do not stick out from the façade, and they can be opened during the frequently wet Connecticut weather. The true double hung also allows for top ventilation to vent hot air from the house.

The number of windows on the east, north, and west façades were minimized. However, their sizes were determined by egress requirements, and their glazing was “tuned” to the orientation. These windows have a U-value of 0.29. 

The house is sun-tempered, meaning most of the windows face south. These windows perform a different function than the other windows in the house; so, to achieve a higher solar heat gain coefficient, we had to accept a slightly higher U-value. The sunroom is thermally isolated from the rest of the house and can be closed off when the sun is not shining, which minimizes the losses from these windows.

The overhang, a classic feature of bungalows, is designed to shade all the south glass from the high summer sun, while allowing low winter sun to penetrate the sunroom. 

The whole house infiltration rate was measured at 0.8 air changes per hour at 50 Pa. The framer and insulation contractors were diligent about sealing penetrations. Only one blower door test was performed at the end of construction as part of the energy certification process.

Heating, Ventilating, and Air-Conditioning
The space heating system is a 1.5-ton air-to-water heat pump using CO2 for the refrigerant (COP = 3.7). This provides heat to a 12-zone radiant floor system as well as for domestic hot water. (I’m a mechanical engineer, so I had to have lots of zones!) A heat exchanger isolates the radiant system from the domestic hot water. An 80-gallon storage tank meets hot water demands.  

On sunny days, the sunroom can heat the house. Small windows at the top of the sunroom allow hot air to enter the second floor. An opening on the north side of the house between the upstairs balcony and the living room completes the air circulation pattern to move solar heat throughout the house without fans.


Interior of the sunroom after insulation has been installed, but prior to the plaster board installation.

Karla Butterfield


The windows and floor plan allow breezes to flow freely through the house for natural ventilation. Cool air can enter through the walkout basement on the lowest level of the house and exit through the second floor, especially when it isn’t windy. This allows us to ventilate the house at night for cooling and close it up during the day to preserve the coolness of the previous night. We’ve found this to be an effective cooling mechanism—even when outdoor temperatures exceed 94ºF, the house temperature has not exceeded 74ºF. The result is that the house requires very little mechanical cooling. 

However, to qualify for the utility rebate for zero energy houses,1 we had to get a HERS rating2 from a certified rater. This required that we add some high-efficiency air conditioning. The house also met the requirements of the DOE Zero Energy Ready Home.3 A single mini-split heat pump (1.5 tons) in the living room provides cooling, dehumidification, and supplemental heating (SEER = 26.1, HSPF = 11.5). Note that the cost of adding this unit was significantly below the rebate for the zero energy house. During the summer of 2017, we didn’t use the unit, but we did use it for a week in 2016. 

We also find that the unit is very effective in heating mode to recover house temperatures from a night setback, because the radiant floors are slow to respond. An air-to-air heat exchanger (sensible only) provides fresh air (1.1 cfm/W) to the bedrooms and exhausts air from the general kitchen area and the bathrooms.

Renewable Systems
The 9.4 kW PV system is mounted on the south roof. The installation has only one roof penetration for the electrical and is attached to the standing seams on the roof. The wiring was done as part of the electrical rough-in. The system uses two 5 kW grid-tied inverters. When the grid fails, the inverters can generate electricity up to 3,000 W through an emergency circuit if the solar resource is available. We didn’t include batteries, although the overall electrical system is designed to accommodate future batteries. 

We chose materials carefully to minimize the introduction of volatile organic compounds as part of the effort to minimize indoor pollutants that would need to be ventilated from the space. A mineral-based paint was chosen because of its minimal offgassing. There was no “new paint smell.”

Locally harvested quarter-sawn white oak floors were finished with tung oil using a citrus-based solvent. The tongue and groove floorboards were considered seconds and cost roughly the same as plywood. Natural linoleum with a floating floor system was used for the kitchen and sunroom (no adhesives). Metal kitchen cabinets from 1959 were salvaged from two houses in Connecticut undergoing kitchen remodels. 

We designed the house to minimize water consumption. The graywater and blackwater drains are separated. Graywater could be recovered, and blackwater can be diverted to a composter. The toilets are designed to use 1 pint or less per flush and are very effective, with the added bonus that cleaning the bowls requires very little effort (and minimal chemicals). The standing-seam metal roof provides clean rainwater we could collect in the future.

Now the rest of the water story. The house is on a well and septic system. When we drilled the well, we realized we have a true artesian well when it overflowed the well cap. That means we have an abundance of water, but we’re still conservative about how we use it.
The septic system is effective at managing graywater, and we haven’t put much effort into recovering graywater and harvesting rainwater. The capability is there for the future, though. 

Energy Performance
The HERS rating on the house is 35 without the PV system and 2 with the PV system.6 The house was metered in for the 2017 calendar year. PV offset 84% of the 11,734 kWh consumed. (The PV system produced 9,896 kWh, or 1.05 kWh/Wdc.) The design estimate was 15,006 kWh and 12,368 kWh, respectively. The intent was that our plug loads would be less than the estimate of 7,562 kWh, which they were, coming in at 6,573 kWh. The cooling loads were also smaller than the design loads. 

The reduced PV production is a result of snow cover and low angle tree shading. Some plug loads exist that are not typically found in residential buildings. These loads consume 2,154 kWh. (See "The Footprint: Out of the Typical Residential Box.") If these loads were removed from the consumption totals, the house would have generated more energy than it consumed, even with the reduced PV output (Figure 2).

Integrating the architecture and energy performance of a house was accomplished at a typical market price for new construction in northeastern Connecticut. The house is sun-tempered, superinsulated, and very tightly constructed. A mechanical system designed to complement the envelope consists of a mini-split heat pump and an air-to-water heat pump. The PV system did not perform as expected mainly due to snow cover and some shading; however, the house was measured to perform well and can achieve zero energy status if nontypical residential loads were excluded. If these loads are included and on-site wood is used for heating and cooking, this provides an alternative pathway for zero energy.


Zero Energy Family Life

Paul and Julia with their three boys and Scramble the Duck. Scramble, a special member of the family, has become a state-wide celebrity—see

For us, zero energy is a lifestyle choice. Yes, we designed the house with elements that just work—such as window orientation, insulation and LED lighting. However, each component of life deserves scrutiny of its value. We don’t care that we don’t have a dishwasher, TV (we had one and no one ever turned it on) and rarely use the dryer. 

Our lifestyle has created a family of avid readers, musicians and animal caregivers. Our three boys get dirty, and we use a front-loader washer to clean their clothes (sorry, no washboard); the clothesline is gentle on clothes (naturally sanitized by the sun), dishes are cleaner, and hobbies include gardening, cooking and trying to minimize our environmental footprint. 

If we really want to make a difference for sustainability and creating a healthy environment, we need to look at all the decisions that we make. Living a zero energy lifestyle has been good for the family. 

Photo: Eversource Energy



  1. EnergizeCT. 2018. "Residential New Construction Program."
  2. RESNET. 2018. “What is the HERS Index.”
  3. DOE 2018. “DOE Zero Energy Ready Home.”  
  4. EnergizeCT. 2018. 2015 Challenge Participant: Torcellini Residence.

About the Author
Paul Torcellini, Ph.D., P.E.,
is a principal engineer at the National Renewable Energy Laboratory and is on the faculty at Eastern Connecticut State University.

View the PDF: HPB Spring 2018_Zero Energy House.pdf
Categories: Net Zero Energy, Zero Energy House