Housing in a Hurry? This Passivhaus-Certified Modular Building Is All-Electric

Montgomery Sisam Architects show how it's done in Hamilton.

King William Housing exterior

Montgomery Sisam

Cities are facing a housing crisis and need a solution. We need housing in a hurry; speed is one of the promises of modular housing. We need buildings that use very little energy and have low carbon emissions; that’s one of the perks of Passivhaus (or Passive House) certification. We need structures built of materials with low upfront carbon emissions; that’s one of the benefits of wood frame construction.

Enter Montgomery Sisam Architects. It pulled off the hat trick (a hockey term for getting three goals in one game) with a small project in Hamilton, Ontario that is modular, Passivhaus, and features a wood frame.

The three-story building has 24 studio units, four at grade and the balance, on the two floors above. The ground floor is otherwise dedicated to shared amenities such as a community room, meeting room, lounge, and laundry facility.

angled view of building

Montgomery Sisam

The architects wrote, "It will sit on the site of a former surface parking lot between a church and multi-unit residence and is designed in deference to its neighbors with a similar set back, height, and roofline."

This is amusing because it is sitting among the usual grungy Hamilton mix of parking lots and industrial buildings, with the building to the right being the only one in the neighborhood with this height or roofline and it is no charmer. But Montgomery Sisam has always been sophisticated, respectful, and deferential in their work, so it is not a surprise that they would try. 

view of garden courtyard

Montgomery Sisam

Like many good Passivhaus designs, the building has a simple form. And like many Montgomery Sisam designs, it works because they have a good eye for proportion and can make it elegant, which architect Bronwyn Barry hashtags #BBB: "Boxy But Beautiful."

Montgomery Sisam wrote, "The glazed front entrance and rear exit are strategically aligned to create a visual connection between the street and rear yard. The yard is designed to be an animated space, featuring barbecues, seating, and a community garden surrounded by lush, low-maintenance landscaping."

The project is all-electric and has solar panels on the roof. Principal Enda McDonagh tells Treehugger that the client, City Housing Hamilton, is always "pushing the sustainable boundaries." He's also a certified Passivhaus consultant, although Andrew Peel of Peel Passive Consultants, who has worked on several projects shown on Treehugger, was brought in on this one too, as a consultant to ensure it hit the International Passivhaus standard. 

McDonagh tells Treehugger the modules were built by NRB Modular Solutions, located nearby in Grimsby, Ontario, so the 14-foot-by-65-foot long units didn't have to travel far, but NRB has built affordable and social housing as far away as Honolulu.

Upper floor plan

Montgomery Sisam

In the typical floor plan, you can see how how the modules line up and admire a few of the nice design touches. The main stair is generous, with natural light, and far more welcoming than most stairs in apartment buildings. There are also windows at each end of the corridor. This is not what you usually see in budget buildings where every square foot has to be value-engineered. Our plan man Mike Eliason might complain about the center corridor and the two stairs, but this works.

Unit plans

Montgomery Sisam

The units themselves are interesting as well, with a generous entry area and a lot more kitchen than I would have expected in a unit this small. The big box behind the toilet is for mechanical services; this is common in modular housing where all the plumbing and other services are done in the factory, but the vertical connections can be conveniently made from the corridor side of the unit.

The constant ventilation and fresh air required in Passivhaus is ducted from a central Energy Recovery Ventilator (HRV) to a Variable Air Volume (VAV) box in the unit.

Typical unit interior

Montgomery Sisam

One of the key points of Passivhaus certification is the testing for airtightness; air infiltration cannot exceed 0.6 times a room's volume per hour, and the pressure differential is limited to 50 Pascals. This can be tough in modular construction, where the control surfaces are not continuous.

What Is Passivhaus?

Passivhaus (or Passive House) is a building concept where heat loss or gain through the walls, roof, and windows is drastically reduced by the use of insulation, high-quality windows, and careful sealing. It's called "passive" because much of the heating required is met through "passive" sources such as solar radiation or the heat emitted by occupants and technical appliances.

When Monte Paulsen was consulting on what was probably Canada's first modular Passivhaus building in Bella Bella, British Columbia, he had blower door tests done on every module individually in the factory. That would be hard in the Hamilton design because each module has two units and a bit of corridor down the middle. 

closeup windows cropped

Montgomery Sisam

McDonagh explains the Hamilton building modules would be set, and then the entire structure would be wrapped with insulation and cladding onsite. The windows are installed in factory modules, sticking out so that they sit within the exterior cladding. It sounds like a bit of a nightmare, matching up the cladding to the windows and getting a tight seal, but at least if there is a leak it can be found and can be fixed.

One of the reasons modular construction hasn't lived up to its promise was that with most other industrial products, you get a lot of repetition and once you get over the learning curve, it becomes faster and cheaper. Modular builders never seemed to get enough repetition; every building was different.

This is also a problem with Passivhaus, where trades have to learn the importance of careful sealing and real precision. Montgomery Sisam is certainly ramping up that learning curve; this building seems so much more sophisticated and refined than their first modular buildings in Toronto.

Now they have an all-electric, Passivhaus model that's nice enough to look at that even a NIMBY could love it. It could be ordered up for any lot, just about anywhere, and because it is modular, at a predetermined price and schedule. Given the housing and climate crises that we face, I hope that we will see a whole lot more of these.