Image Credit: Lehto Design/Build Wolfworks was the co-winner of the CT Zero Energy Challenge with this design in Farmington, Connecticut. The firm also won the top prize the previous year.
Image Credit: Wolfworks The kitchen of the Killingly house. With a conventional truss roof above, the timber trusses don't have to provide structural support. The ceiling is insulated with dense-packed cellulose.
Image Credit: Lehto Design/Build An open design makes heating and cooling easier. The 2,619-square-foot house submitted by Nick Lehto is conditioned with a Mitsubishi ductless minisplit heat pump.
Image Credit: Lehto Design/Build The Farmington house is heated and cooled with a ducted minisplit concealed in the ceiling. The system has a single supply line for the main level and a single supply for the lower level.
Image Credit: Wolfworks Getting a look at the details: A mid-construction tour of the Farmington house built by Wolfworks offered a close look at the double stud-walls, insulated with a combination of dense-packed cellulose and polyisocyanurate insulation.
Image Credit: Wolfworks
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 HERS 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 Passivhaus-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 pump,” 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 2×4 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 sheathing and 3M 8067 flashing tape for the air barrier 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 test 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 heater 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-factor of 0.18 and a solar heat gain coefficient of 0.26.
- A roof-mounted photovoltaic 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 energy 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 fog 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 2×4 wall and dense-packed that. Above-grade walls have an R-value 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 2×6 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, which Wolf describes as “pricey and fabulous, beautifully engineered and easy to install.”
- A heat-pump water heater.
- Triple-glazed SchÃ¼co 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.”