Two Builders Will Share Top Connecticut Prize
Lehto Design/Build and Wolfworks win the CT Zero Energy Challenge, a competition that honors energy efficiency and low environmental impact
Two Connecticut builders can claim top honors in the most recent CT Zero Energy Challenge, a design competition that promotes high-efficiency houses with a low environmental impact.
Nick Lehto and Jamie Wolf are both being recognized as Overall Winner, and each will apparently receive a $10,000 check. Scores were based on judging in four categories: lowest overall HERSIndex or scoring system for energy efficiency established by the Residential Energy Services Network (RESNET) that compares a given home to a Home Energy Rating System (HERS) Reference Home based on the 2006 International Energy Conservation Code. A home matching the reference home has a HERS Index of 100. The lower a home’s HERS Index, the more energy efficient it is. A typical existing home has a HERS Index of 130; a net zero energy home has a HERS Index of 0. Older versions of the HERS index were based on a scale that was largely just the opposite in structure--a HERS rating of 100 represented a net zero energy home, while the reference home had a score of 80. There are issues that complicate converting old to new or new to old scores, but the basic formula is: New HERS index = (100 - Old HERS score) * 5. index, lowest HERS index without renewable-energy add-ons, lowest cost per square foot, and lowest projected annual net operating costs.
Lehto Design/Build's entry was a 2,619-square-foot single-story home in Killingly, Connecticut.
Wolfworks won for a 2,932-sq/ ft. house in Farmington, Connecticut. It's the second such award for Jamie Wolf, the design/build firm's principal. A PassivhausA residential building construction standard requiring very low levels of air leakage, very high levels of insulation, and windows with a very low U-factor. Developed in the early 1990s by Bo Adamson and Wolfgang Feist, the standard is now promoted by the Passivhaus Institut in Darmstadt, Germany. To meet the standard, a home must have an infiltration rate no greater than 0.60 AC/H @ 50 pascals, a maximum annual heating energy use of 15 kWh per square meter (4,755 Btu per square foot), a maximum annual cooling energy use of 15 kWh per square meter (1.39 kWh per square foot), and maximum source energy use for all purposes of 120 kWh per square meter (11.1 kWh per square foot). The standard recommends, but does not require, a maximum design heating load of 10 W per square meter and windows with a maximum U-factor of 0.14. The Passivhaus standard was developed for buildings in central and northern Europe; efforts are underway to clarify the best techniques to achieve the standard for buildings in hot climates.-certified home his firm built in Harwinton was the 2012 contest winner.
Among eligibility requirements: single-family and multifamily projects must have a HERS index of 45 or less without renewable energy systems and be new construction or a complete gut rehab. The contest is sponsored by Energize Connecticut, an initiative that helps homeowners, renters, and businesses use energy more efficiently.
Green Building Advisor was unable to reach the contest administrator for scoring details, but Lehto and Wolf thought the results would be formally announced a little later in the year.
A family farm is the setting for Lehto project
Lehto's clients were a couple who live on a farm that has been in the husband's family for a century. They occupied an old farmhouse on the property, the same house where the husband had been born. But the woman was interested in moving into something more up to date — just not too contemporary.
"Her initial thought was that an energy-efficient house would have to be some type of modern cube," Lehto said, "which I think, sadly, a lot of people have that stereotype. When she saw that the homes we did basically look like normal homes she was very interested in going forward. The more she involved she got, the more she learned, the more excited she got about the whole thing."
They brought Lehto plans for a home with some Arts & Crafts detailing, which they had purchased at a web site called The Red Cottage. He modified the floor plans, reoriented the garage and applied energy-efficient construction practices. The house has two bedrooms and two bathrooms.
Lehto came to the building trades early. His father and uncle are both builders, as are two of his cousins. But it was in 2008, on a trip to Finland, that Lehto was first introduced to some unfamiliar building components. "That was the first time I'd ever encountered an air-source heat pumpHeat pump that relies on outside air as the heat source and heat sink; not as effective in cold climates as ground-source heat pumps.," he said. "Growing up in New England, I didn't know an air-source heat pump even existed. The fact that they were using them in that climate, I was pretty impressed. And basically they don't have any windows that aren't triple-paned. That really opened my eyes as to what was available."
He returned to the U.S. a convert.
Straightforward construction, tight building envelope
The double 2x4 stud exterior walls are 12 inches thick and filled with dense-packed cellulose to R-45 (Lehto has his own insulation blower because he's had trouble finding an insulation subcontractor in his area that does cellulose). The trussed roof is insulated to R-70 with 20 inches of blown-in cellulose.
He used nothing more exotic than plywood sheathingMaterial, usually plywood or oriented strand board (OSB), but sometimes wooden boards, installed on the exterior of wall studs, rafters, or roof trusses; siding or roofing installed on the sheathing—sometimes over strapping to create a rainscreen. and 3M 8067 flashing tape for the air barrierBuilding assembly components that work as a system to restrict air flow through the building envelope. Air barriers may or may not act as a vapor barrier. The air barrier can be on the exterior, the interior of the assembly, or both. in the exterior walls. Gypsum drywall is the ceiling air barrier. Where partition walls meet the ceiling, Lehto sprayed polyurethane foam from the top to seal potential leaks.
A blower-door testTest used to determine a home’s airtightness: a powerful fan is mounted in an exterior door opening and used to pressurize or depressurize the house. By measuring the force needed to maintain a certain pressure difference, a measure of the home’s airtightness can be determined. Operating the blower door also exaggerates air leakage and permits a weatherization contractor to find and seal those leakage areas. measured air leakage at 0.38 air changes per hour at a pressure difference of 50 pascals (ach50).
Other features include:
- A foundation made of insulated concrete forms (R-22); there are also 4 inches of extruded polystyrene insulation under the slab (R-20).
- A State heat-pump water heaterAn appliance that uses an air-source heat pump to heat domestic hot water. Most heat-pump water heaters include an insulated tank equipped with an electric resistance element to provide backup heat whenever hot water demand exceeds the capacity of the heat pump. Since heat-pump water heaters extract heat from the air, they lower the temperature and humidity of the room in which they are installed. for domestic hot water, and a three-head Mitsubishi ductless minisplit air-source heat pump for space heating and cooling.
- Triple-glazed Mathews Brothers windows with a U-factorMeasure of the heat conducted through a given product or material—the number of British thermal units (Btus) of heat that move through a square foot of the material in one hour for every 1 degree Fahrenheit difference in temperature across the material (Btu/ft2°F hr). U-factor is the inverse of R-value. of 0.18 and a solar heat gain coefficient(SHGC) The fraction of solar gain admitted through a window, expressed as a number between 0 and 1. of 0.26.
- A roof-mounted photovoltaic(PV) Generation of electricity directly from sunlight. A photovoltaic cell has no moving parts; electrons are energized by sunlight and result in current flow. array rated at 8.5 kilowatts.
Wolfwork's design also uses double stud walls
Jamie Wolf's clients wanted a smaller retirement home, something he sees a lot these days. Wolf combined net-zero energyProducing as much energy on an annual basis as one consumes on site, usually with renewable energy sources such as photovoltaics or small-scale wind turbines. performance with Sarah Susanka's Not-So-Big-House thinking to produce the 2,932-square-foot three-bedroom home in Farmington.
One key to high performance is a "sandwich wall" that combines dense-packed cellulose and rigid polyisocyanurate foam board. The structural outer wall is built with 2x6s, the inner wall with 2x4s. The air barrier is Huber's ZIP system sheathing, taped at the seams.
"We build that first wall, and our air barrier is complete," Wolf explained. "When we build that first wall, we do a fogTo fog a room or building is to use a fog machine during a blower door test, revealing locations of air leaks where the fog escapes. The fogging material is usually a glycol-based solution, completely non-toxic. test and a blower door test then so if there's anything that needs to be fixed we can see it and get at it and we can fix it."
Next, Wolf added dense-packed cellulose to the outer wall, installed 3 inches of rigid foam, and then built the inner 2x4 wall and dense-packed that. Above-grade walls have an R-valueMeasure of resistance to heat flow; the higher the R-value, the lower the heat loss. The inverse of U-factor. of 50.
"It's worked really well for us," he said, "because it's easy for everyone to understand how to build it. We just tell the framers the interior wall is just another partition wall and it's built at the same time the partition walls are built."
The outer framed wall is built 24 inches on center; the inner wall at 16 inches o.c., which Wolf says keeps trim carpenters happier. The two walls are tied together with plywood window bucks sealed with Siga tape.
The air barrier at the ceiling level is a layer of plywood applied to the bottom chord of the roof trusses. That may be a little unconventional, but Wolf says it helped remind subs on the job how important it was to keep the air barrier intact.
Foundation walls are insulated on the inside with 2 inches of polyiso rigid foam, plus a 2x6 stud wall filled with dense-packed cellulose for a total R-value of about 34. There are 6 inches of expanded polystyrene (EPS) under the slab, rated at R-24.
Airtightness was measured at 0.49 ach50.
Heating and cooling with a ducted minisplit
Wolf chose a single-ceiling-head Fujitsu ducted minisplit for heating and cooling. The system has a single supply for the main level of the house, and a second supply for the lower level. There's a single, short return duct on the main floor.
There are no separate supplies for the bedrooms and other separated spaces. In winter, if you close a door to the bedroom at night, the temperature in that room will slowly sink. Wolf's clients were satisfied the system would work for them, but he points out that it's not the kind of heating and cooling system for everyone.
"To do this, two things are important," Wolf said. "One is that you have this level of performance, a Passivhaus-level building envelope so that the rate of heat loss is really slow. What happens is these spaces stabilize at an even temperature so it doesn't take very much to bring them back up to temperature."
Also, anyone living in a house with a similar system has to be OK with leaving doors to bedrooms and other spaces open most of the time. "This is not a home where, let's say, your young adult lives with the door closed all the time," Wolf said.
Other features of the house:
- A Zehnder heat-recovery ventilator(HRV). Balanced ventilation system in which most of the heat from outgoing exhaust air is transferred to incoming fresh air via an air-to-air heat exchanger; a similar device, an energy-recovery ventilator, also transfers water vapor. HRVs recover 50% to 80% of the heat in exhausted air. In hot climates, the function is reversed so that the cooler inside air reduces the temperature of the incoming hot air. , which Wolf describes as "pricey and fabulous, beautifully engineered and easy to install."
- A heat-pump water heater.
- Triple-glazed Schüco windows.
- A 10-kW photovoltaic array.
Wolf is getting very good performance out of relatively straightforward building techniques and ordinary materials. "There are two parts to this," he said. "There's designing it and building it. And the whole point is that in the design phase you have to have a pretty sophisticated understanding of all the principles that make these houses work.
"But if you design those in," he added, "you kind of bake them into the design, and think practically as a builder, too, it's very doable. It's not hard to show people how to do it even if they haven't done it before."
- Lehto Design/Build
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