Solterre Passive House Concept Cottage
Last summer, I took a drive from Halifax down to Lunenburg County, Nova Scotia, to check out Solterre Design’s Concept Cottage. The house looks like it’s been there for a few decades, settled into the top of a gentle hill on the edge of a rolling meadow, with a stunning view of the waters around the area known as Second Peninsula. It’s hard not to fall in love with it in a capital-letter Romantic way. But that’s not the best part.
This off-grid house is certified LEED for Homes Platinum, and also meets the German Passivhaus (PH) standard. In 2012, Solterre won a Nova Scotia Lieutenant Governor Award of Merit for the project, and 2014 brought the ScotiaBank Ecoliving Business Leadership Award.
The 1,500 ft2 three-bedroom house is based on some pretty straightforward goals. They are
- to showcase the principles of what Solterre Design does;
- to maximize passive-solar usage;
- to try out many new materials and assemblies at their own risk;
- to showcase Nova Scotia building materials, services, and technologies;
- to get off the grid; and
- to meet LEED Platinum and PH certifications.
I first met Keith Robertson and Jennifer Corson, principals of Solterre Design, through Solar Nova Scotia, back in the day when they were students at the architectural school in Halifax and I was writing and illustrating a book on solar home design. Twenty-plus years later, we’re standing in the living room of this award-winning cottage, comparing notes on our kids and talking shop.
What I really like about the Concept Cottage is the transparency. Yes, there are gloriously large windows that open out onto a gloriously large view of a meadow and the inlets around Lunenburg. The place is charmed, but that’s not what I mean. Keith and Jennifer have made the whole operation of the building transparent, including a web-accessed server where you can see data on how the house is performing (see “learn more”).
The house also builds on Jennifer’s longtime commitment to recycling and repurposing (she is a founding partner in Renovator’s Resource, an architectural salvage business that started in 1994). The interior doors are salvaged from a set of doors taken from a 19th century estate in Halifax when it was undergoing a major renovation. The kitchen cabinetry is out of an old hospital, most of the wall trusses came from a movie set, and the polished concrete floor features about 16 tons of recycled glass aggregate.
More recycled glass, about 77 tons of it, was used in the septic bed instead of sand media. This was the first time that finely crushed glass, also called glass sand, was used in an approved septic field in Nova Scotia. Given the large proportion of houses on septic systems in the province, it will be interesting to follow the uptake of this replacement material.
Did I mention how much I am in love with the tub/shower surrounds? They are repurposed Plexiglas and acrylic display signs.
The thermal envelope I fall in love with in a different way. The slab-on-grade construction is brilliant, a three-piece rigid-foam slab form designed by Solterre and Natalie Leonard, principal of Passive House E-Design, in conjunction with local foam insulation manufacturer TrueFoam. This design essentially creates a rigid-foam wading pool, ready to be filled with concrete.
Although the foam “wading pool” was a new take on forming the foundation, the local contractor said that the learning curve was short, and the foundation went together in a matter of days.
The toe-up piece of the foundation insulation form is partially covered by the exterior insulation of the walls. It consists of a Larsen truss made from salvaged wood I-trusses on the north, east, and west walls and 3 inches of polyisocyanurate on the south wall. (See Figure 1 for more wall detail.)
The three-bedroom, accessible house was designed in a classic passive-solar pattern, with the open living spaces to the south and the bedrooms, bath, storage, and mechanical rooms to the north. To create flexibility in the living spaces, doors act as movable partition walls. (See Figure 2 for the floor plan.)
An outbuilding compensates for the loss of the basement as storage space, but the design of the living space incorporates plentiful storage in the slab-on-grade house.
Outside, the focus was on xeriscaping, with no potable water used for landscaping. In addition, rainwater collected from the metal roof is stored in a cistern for interior and exterior use. High-efficiency DC pumps and a dug well feed the water to the house.
The only complaint I heard about the mechanical systems in general was about the noise level of the DC pumps. While it looked like there was a bit of an installation challenge with the pump, the noise level is probably so very noticeable because the house is so well insulated as to be soundproofed, and the other systems in the house are very quiet. A new submersible pump is planned to solve the noise problem. (See “Concept Cottage Design Considerations” for a summary.)
Concept Cottage Design Considerations
- Orient for best possible solar gain and view lines.
- Protect the home from SW and NE winds.
- Provide maximum affordable insulation levels.
- Provide effective natural ventilation and efficient mechanical ventilation.
- Provide compact, efficient layout for small footprint.
- Maintain affordable construction and operating costs.
- Use locally available products, equipment, and salvaged materials.
- Meet the Lifetime Standard for accessibility.
- Provide heat, water, and cooking fuel 24/7.
PH features such as high insulation levels, airtight construction with no thermal bridging, and high-performance windows ensure that the passive-solar and internal heat gains are optimized. The key to the whole concept being attention to details and appropriate materials at a very early stage in the design process.
The Larsen truss walls are built out of salvaged open-web wood trusses, and the cavities are filled with dense-pack cellulose. To ensure that the cellulose was blown in at the proper density, baffles of woven olefin were installed to create a discrete cavity between each set of trusses.
The south wall was built using 2 x 8s, due to the large percentage of glazing to wall ratio. This wall was filled with rock wool insulation, with 3 inches of polyisocyanurate on the exterior.
There are two superinsulated roof assemblies. The metal roof provides rainwater collection for potable water and a mount of the solar hot-water collectors. The sod roof was constructed using a traditional Faroe Islands technique.
The detailing and attention paid to the air barrier across the various assemblies results in a continuous air barrier throughout the house. The windows and doors are sealed to plywood bucks that tie into the rough stud openings. The top plates of the walls are wrapped to make the transition from the exterior air barrier to the oriented strand board on the ceiling that acts as an interior air barrier. There is no 6-mil poly anywhere in the house.
Triple-glazed, argon-filled windows feature an insulated fiberglass frame with an insulating spacer and custom low-e coatings (selective glazing) to match the heating/cooling/shading strategy of the window’s orientation. (See “The Concept Cottage at a Glance.”)
The Concept Cottage at a Glance
Building Envelope:Slab: R-33
Windows: R-3.6–5.1 (U-18–22)
ACH at 50 Pa < 0.6
Annual heat load: 1,971 kWh
Peak heat load 9,370 Btu/h (2.75 kWh)
Climatic Information:Lunenburg, Nova Scotia (44.4°N, 64.3°W)
Design temperature: 3.2 °F (–16°C)
Heating degree-days: 7,861 °F (4,367 °C)
One of the recurring themes that I keep coming across when I talk to the people who are designing and building high-performance houses like the Concept Cottage is this: We overdesigned the mechanicals. And the Concept Cottage is no exception.
This house has a solar-thermal system that services both DHW and space-heating needs. The four-panel system is oversized for domestic hot water use in the summer, but a drainback tank prevents the system from overheating. A propane-fired water heater backs up the solar-thermal system. (Propane is also used for the kitchen stove.)
The supplementary space heating is delivered by low-temperature hydronic baseboards fed by the solar-thermal and the propane water heater as required. A small, high-efficiency woodstove in the living area also provides secondary heating. Except: The hydronics aren’t needed. The house has never dropped below 60°F (13°C), even in the depths of cold winter nights when it’s been unoccupied for weeks.
Three hundred feet of PEX piping makes a loop below the slab insulation to act as a ground source preheater to the 95% efficient energy recovery ventilator. (See Figure 3 for a visual representation of the home’s mechanical systems.)
Get live data showing how the Concept Cottage is performing.
The off-grid house has all of the “mod cons”—TV, Internet, fridge, freezer, laundry equipment, dishwasher—all running off solar power. While the house is not occupied full time, the 3kW system, with an estimated annual production of 2,400 kWh, can meet the occupants’ needs. A run of cloudy weather requires a bit of attention to energy budgeting. Small appliances that rely on electric-resistance heating (toaster, kettle, coffeemaker) are switched out for ones that can be used on the propane cooktop, for example. A gasoline backup generator is on-site to charge the batteries if needed.
A Special Kind of Love
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