A net-zero home builder finds opportunity during frigid temperatures
Bruce Murdoch has seen the light and it came on a crisp, cold day in Cranbrook, BC.
It was just last month and the Kootenays—like much of Canada at the time—was in a deep-freeze. Temperatures had plunged to nearly -40 degrees. The builder and owner of K-Country Homes saw this as the perfect opportunity to check the performance of Cranbrook’s first net-zero home, a two-unit residential building he completed in 2022.
His realization that day?
“I’m convinced more than ever that every builder can and should be building net-zero homes right now, even in our climate,” says Bruce, who has been building homes for more than 30 years. “But we need to share what we’re learning about how to do it. This cold snap gave me new information about how best to size heat pumps and supplementary heat.”
As a net-zero building, this Cranbrook home produces as much energy as it consumes on an annual basis using an on-site renewable energy system. Electricity is generated by solar panels high on the two-and-a-half story building’s roof. Because solar panels produce more electricity in summer than in winter, the building is also connected to the BC Hydro grid, ensuring consistent supply year-round.
But, crucially for its net-zero designation, there is no natural gas connection and no furnace.
No furnace?!
Nope. Instead, the home relies on two cold-climate heat pumps, one for each unit. Heat pumps work by transferring heat from outside to inside, which is much more efficient than using energy to generate new heat. While a high efficiency furnace can approach 99% efficiency, heat pumps can actually reach 300 or 400% efficiency.
That’s why heat pumps are Bruce’s favoured technology for a net-zero home like this, where energy use must be kept as low as possible (in fact, this home uses only about half the energy of a typical new home).
The unintuitive thing about heat pumps is they work even in cold weather. Even at −25°C, there is still warmth in the air, it just takes a bit longer and requires more energy to gather it. Bruce installed cold-climate heat pumps with design features ensuring they continue to work in the depths of a Canadian winter.
He also installed electric wall radiators as backup, designed to turn on only when the heat pumps can’t keep up during very cold temperatures. In winter 2022–23, this happened only once. “During a six-day period with temperatures dropping to −35°C, there was only a very short timeframe that required backup heat,” explains Bruce. It was such a short blip that he estimates it only cost an extra $4.
Bruce Murdoch’s data shows how little the home’s electricity consumption peaked when temperatures dropped in winter 2022.
This winter’s cold snap was more challenging because temperatures dropped further and for longer. “We found that the basement suite and the upper floor of the upstairs suite were fine. It was the main floor where we couldn’t quite keep up with the heating demand for a couple of days,” says Bruce.
The experience has prompted him to think about how to factor heat pump efficiency and the height of his buildings into his heating and cooling calculations. “Because warm air rises, maybe we need to somewhat overdesign the heating system for the main floor and under design for the upper floor.”
“Bottom line: it all comes down to design. We are definitely ready for heat pumps in Climate Zone 6 but we need to be very thoughtful about design.”
Think through the design of every single room
It’s a challenge that Bruce welcomes. Thinking deeply about the design of his buildings is already a point of pride—and crucial to successfully building any net-zero building. Decisions must be made about every part of the building envelope: the exterior walls, foundation, roof, windows, and doors.
Consideration is given to occupant comfort and to reducing energy demand. “Because we focus on the integrity of the building envelope, the home retains heat very well,” Bruce explains.
There are a few factors that helped the building envelope to perform so efficiently.
First, the home was built with structural insulated panels (SIPs) that provide R-16 insulation under the basement slab, R-40 insulation in the basement walls, R-30 insulation in other walls, and R-45 insulation in the attic. The windows that are mostly triple-glazed.
Second, Bruce worked closely with a registered energy advisor from the very early planning stages. His energy advisor offered advice throughout the design stage, even applying energy modeling tools to help finalize design decisions. Once construction was complete, the energy advisor conducted a detailed survey of the home, including a blower door test to confirm the home’s achieved energy rating.
“It’s key that we use an energy advisor on this type of project. They provide a heating and cooling load estimate for every single room,” explains Bruce. This means an HVAC technician can understand how changes to the overall system affect different spaces—which in turn lets the builder find the optimal solution that best serves the whole house.
That’s the benefit of viewing the house as a fully integrated system. While the various components of a home can be viewed as separate features, they all interact with and impact one another. Only by looking at these features in an integrated fashion can builders properly balance the complex interactions and achieve a net-zero energy system.
Premium comfort, without premium cost
For this build, Bruce brought his building costs down to under $300 per ft2, comparable to the price of a code-built home. Using Structured Insulated Panels (SIPs) instead of standard wood construction halved his labour costs, by his estimation. And it shortened the construction time frame to just 8 months, which comes with related financial savings.
“Net-zero homes are economical,” says Bruce. “When experienced construction companies think carefully and apply the fundamentals of energy-efficient home design and go the extra mile in certain areas such as ensuring air tightness, it’s more than feasible to achieve net-zero. With that comes a major financial benefit for the homeowner: no energy costs—ever.”
Key stats about this home
Configuration: Two-unit home with main residence on the main and upper floors, as well as a basement suite.
Size: 2,350 ft2
Cost to Build: $625,000
Operational GHG Emissions: 161 kg CO2e per year
Air tightness: 1 air change per hour
Climate Zone: 6
Insulation: Structural Insulated Panels
- R-16 basement slab
- R-40 basement walls
- R-30 other walls
- R-45 attic
Windows: Triple-glazed, average U-value of approximately 1.10. The dining room windows on the south elevation are double-glazed to capture some solar heat gain in the winter without significantly adding to the cooling load in summer.
Heating and Cooling: Two Fujitsu mini-split heat pumps with three heads (one ducted and two non-ducted), Amaze wall panel heaters, and additional supplementary heat in the bathrooms provided by an electric radiant heat system installed under the floor.
Hot water: Heat pump hot water tank and drain water heat recovery.
Other Notables:
- Condensing clothes dryer.
Definitions
Passive House: A voluntary energy-based standard for building design and construction. Passive House (Passivhaus) buildings consume up to 90 percent less heating and cooling energy than conventional buildings.
Net-Zero: A net-zero energy home produces as much energy as it consumes on a yearly basis and has at least one on-site renewable energy system.
Net-Zero Ready: A net-zero energy ready building has been designed and built to a level of performance such that it could, with the addition of solar panels or other renewable energy technologies, achieve net-zero energy performance. This is equivalent to Step 5 of the BC Energy Step Code.
Energy Step Code: The BC Energy Step Code sets performance requirements for new construction and groups them into Steps. Local governments can choose to require or incentivize a given step in new construction. Meeting Step 5 for homes is equivalent to building a net-zero energy ready building.
This exceptional construction project is profiled as part of CEA’s efforts to increase understanding of high performance buildings among local government officials, builders, contractors, developers, and others involved with building, renovating, and marketing homes. These efforts include the Kootenay Clean Energy Transition, which is encouraging the construction of more high performance buildings through implementation of the BC Energy Step Code.
