More Than a Cabin in the Woods: Designing homes using CLT and passive solar strategies

by Katie Daniel | April 8, 2015 2:39 pm

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By Odile Hénault
Tucked in the woods of Saint-Calixte—an hour away from Montréal—is a residential retreat that might have gone unnoticed were its designer not trying to change the way we build and heat our homes. It is an unpretentious statement, advocating better ways of building with wood and simple but efficient harnessing of the sun’s energy. At its own modest scale, this home is becoming one of several projects that will hopefully help the traditional wood industry embark on the 21^st century.

Québec architect Dominique Laroche purchased a site that was a short distance from the city, yet immersed in nature. He had long wanted to experiment with passive solar energy and with a relatively new building technique—cross-laminated timber (CLT) panels.

Despite the half-hectare (1.5-acre) property, he wanted a minimal footprint on the ground, in keeping with his ecological beliefs. The design program was straightforward:

• entry level with an open living, dining, and kitchen area;
• partly cantilevered mezzanine level, with the larger portion used as an office and the smaller space as a reading nook; and
• an additional level below with basic sleeping, bathroom, and multifunctional spaces, along with a mechanical room.

The 114-m² (1225-sf) house is on a steep site, with its lowest level invisible from the road. It is oriented due south—a perfect setting for a passive solar system. The presence of a deciduous forest was a bonus; it would serve as an indispensable condition for the passive solar setup to work adequately, year round.

The promise of CLT panels
Cross-laminated timber panels could be compared to giant sheets of plywood made of solid lumber. Multiple layers (which can vary in depth) are stacked perpendicular to each other, glued and pressed together to make panels that are then machine-cut to size very precisely. Stable and fire-resistant, the panels can be used as walls, floors, and ceilings.

For numerous reasons (including financial ones), Laroche chose to order his CLT panels from the initial manufacturer based in Austria. Although the technology is now fairly widespread in Europe, at the time Laroche designed his project, CLT panels were barely used in Québec, particularly in the single-family housing market.

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One of the most convincing demonstration projects had been built by the Austrian company’s Eastern Canada distributors, which had chosen to expand its headquarters in Longueuil, Que. It had commissioned award-winning Montréal architectural firm Daoust Lestage to design their two-level addition as a showcase for CLT panels. The resulting building was warm, airy, and far removed from the usual industrial structure. It showed both the technical and esthetic promises linked to using cross-laminated timber technology.

The main markets targeted by the industry are the medium size commercial, multi-residential, and institutional buildings, where cost benefits due to its numerous advantages—particularly faster assembly time and overall better thermal performance—are quite obvious. For Laroche, however, there was an added motivation in using the prefabricated panels—it was the possibility of developing relatively complex geometrical shapes without having to produce as many working details as would have been required within a more traditional framework. Communicating a project to a CLT panel manufacturer is simply done through 3-D modelling; panels can then be cut to size to 3.2-mm (1/8-in.) accuracy.

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Using the CLT manufacturer’s tables, engineer Éric St-Georges, ing. M.Sc.A., calculated the structure and integrated the results with the 3-D drawings intended for the manufacturer. The non-CLT structural elements basically consisted of a single 12.2-m (40-ft) long steel beam that supported the roof, and a transversal 4-m (13-ft) long glued-laminated timber (glulam) beam supporting the larger mezzanine. A steel column was introduced between the two, transferring the load from the roof. Another steel column, placed at the southwest angle of the mezzanine level, works in tension, stabilizing the cantilevered floor.

When designing his home, one of the few constraints with which Laroche had to contend was the maximum width for cross-Atlantic shipping. To facilitate stacking in (and removal from) a 2.4 x 12 m (8 x 40-ft) container, panels had to be kept to a maximum width of 2.1 m (7 ft). The project’s longest panels, which were 8.7 m (28 1/2 ft), presented no problem. In the end, the entire house fit into one open-top container.

In terms of timing, the CLT manufacturer received the order on May 7, 2013. Panels were ready two weeks later and were shipped out on May 22. The container arrived in Montréal on June 12, with materials onsite in Saint-Calixte, ready to be unloaded, a week following.

Meanwhile, beams and columns, manufactured by a local company, had been delivered as well as connectors and screws, ordered from a North American supplier by the Montréal builder involved in the project, OÏKOS. With footings and foundation ready, assembly started June 20. It took less than five days to piece the whole thing together, which was about a day and a half longer than expected. The delay was due to heavy rains and the architect refusing to take down a tree that blocked the easiest route. By the end of June, all panels had been assembled—floors, walls, and roof.

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The building was completed during the following months, with the architect allowing himself time to weigh each subsequent move. Windows were installed after the panels, followed by the pouring of concrete slabs—over the CLT floor panels in the case of the entry and mezzanine levels, and directly on the ground at the lower level.

Plumbing and heating elements were incorporated as the floors were being done. For esthetic reasons, most electrical wiring was run on the exterior face of the CLT panels. Insulation was installed: 178-mm (7-in.) blown cellulose for the walls and 203 to 279-mm (8 to 11-in.) polyisocyanurate (polyiso) rigid insulation for the roof, which was then covered with a thermoplastic polyolefin (TPO) reflective membrane.

Two ‘breathable’ membranes—an air barrier and a rain barrier—ensured proper sealing and protection of the building. Finally, untreated red cedar planks, set vertically, were used as exterior finish.

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Passive solar system
The site’s orientation, its 30-degree slope and the omnipresence of deciduous trees on the land created a situation close to ideal for the architect/homeowner when he designed his passive solar system. Obviously, the south façade with its large window openings was to be the main source of heat; the west façade also contributes heat gains, particularly during the spring and fall.

The trio of 100-mm (4-in.) concrete slabs provide a 11.7-m³ (411-cf) thermal mass, which stores solar energy. The thermal mass corresponds to the volume of poured-in concrete—and soapstone used for kitchen counters—acting to capture the heat from the sun and gradually release it. The surrounding trees actually play a major role in this scenario, conveniently losing their leaves in the winter when the sun’s rays are most needed, and growing their foliage again in the spring, providing much-desired shade during the summer.

The dimensions of the openings were fine-tuned by consultant Caroline Hachem, a professor at the University of Calgary’s Faculty of Environmental Design. Triple-glazed windows with a low shading co-efficient film were installed throughout the project, maximizing the sun’s input and minimizing heat losses at night. Backup heating is provided by a hot-water radiant system—the water heated through an instant heater located in the mechanical room. The roof’s shape was determined keeping in mind the eventual use of photovoltaic (PV) or thermal panels, hence the 38-degree angle considered optimal in this particular location.

Additionally, intelligent thermostats were installed in the house, keeping track of daily temperature variations and the exact number of hours each of the three levels was kept comfortable without the backup system being turned on. This information can be obtained directly from the thermostats or by going online. It also allows control at a distance and close monitoring of the house at all times.

The house as experimental ground
FPInnovations is a Québec-based forest research centre, with work that has had ramifications for wood building materials around the globe. When the group became aware of Laroche’s project, it showed interest in using the new house as experimental grounds for measuring the way humidity migrates through the walls.

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Eight probes were installed in various spots, on the east, south, and north façades—some closer to the CLT panels, others closer to the exterior envelope. These probes have since been providing constant readings, which are translated into graphs. Conclusions will not be drawn, however, until two or three years from now, when the house will have gone through full yearly cycles.

The architect chose to leave the panels exposed inside, electing not to install a vapor barrier. Esthetic reasons led to this decision, but so did the desire to benefit from wood’s ability to absorb and release moisture, creating a comfortable level of humidity in the house at all times.

On the exterior, an air barrier membrane wrapped the face of the CLT panels; a rain barrier membrane inserted over the insulation and under the exterior cedar siding provided water protection. Given this particular wall composition, the fact the house is being tested becomes particularly interesting in view of future interventions.

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Conclusion
Laroche’s project is about building small, harnessing a renewable source of energy, and using a natural product not just for its beauty, but also for its properties and ecological benefits. Right from the beginning, this small retreat in the woods was designed as a demonstration project to illustrate alternative ways of looking at construction.

Although some of the CLT panels’ advantages—including cost benefits—may not be as substantial here as they have proven to be with medium-scale buildings, the point is made.¹ Cross-laminated timber panels represent a valid alternative to traditional structural materials. In a country where forests abound, this sends a strong message about the wood products industry.

During the time of this article’s writing, news came of a 13-storey, 94-apartment CLT building is to be erected in Québec City in the coming year. The announcement followed an 18-month negotiation blitz with the Régie du bâtiment du Québec (RBQ), which plays a major role in regulating the construction industry in the province.

Not entirely surprisingly, the one and only manufacturer of CLT panels in the province will be part of the consortium involved in the new multi-residential project. Nevertheless, this is a major breakthrough—one that might truly demonstrate, at a much larger scale than Laroche’s modest home, cross-laminated timber panels’ benefits.

[8]Odile Hénault was trained as an architect in Halifax. After creating and single-handedly producing the architecture magazine Section a, from 1983 to 1986, she had a multifaceted career during which she worked as a critic, editor, curator, teacher, and professional advisor. Hénault can be reached at odile_henault@hotmail.com.

Source URL: https://www.constructioncanada.net/more-than-a-cabin-in-the-woods-designing-homes-using-clt-and-passive-solar-strategies/

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