An innovative Habitat for Humanity pilot project has some concrete ideas about how NetZero Energy homes could be constructed.
In a dramatic shift away from the traditional wood studs and siding approach to home building, cement maker Lafarge Precast and consulting engineering firm Stantec are finishing off Habitat Edmonton’s first pre-cast concrete duplex home as a prototype design to make homes from concrete.
The duplex is designed to be NetZero, meaning over a year its consumption of energy for heating, cooling, lights, water and cooking will be zero. It has photovoltaic and thermal solar panels on the roof and the units also share a geothermal heat pump for heating and cooling. It also takes advantage of the density of the concrete, using its thermal mass to retain heat from the daytime sun and to absorb and deflect heat from the hot winter sun.
The new home is just weeks away from becoming home to two families in the city’s Riverdale community, and once the pilot project is completed, Lafarge wants to see if it can create demand for all-concrete homes as a viable alternative.
Unlike traditional homes which are constructed with wood studs and plywood, this one is made from pre-cast slabs of concrete and then trucked to the site and assembled like a giant Lego set.
There was some concern that the building could looking foreboding and making it look less institutional was one of the first issues the design team tackled.
“We gave the initial designs to our architects and they went to work softening up the exterior,” said Klaas Rodenburg, lead designer at Stantec. “The great thing about pre-cast concrete is that you can do almost anything with it, like add colour and texture.”
There are many advantages to the concept, said Don Zakariasen, Lafarge director of marketing. Quality is controlled and the slabs can be configured with windows and doors and poured with a foam core for better insulation.
As a result, the exterior walls have R44 insulation value and the slab roof has R88. It’s also airtight with triple-glaze high-efficiency windows.
There are 80 separate pieces that make up the duplex, and the basic structure can be put together in a single day. The perimeter walls are concrete — finished and painted like drywall — while the interior dividing walls are standard steel-stud and drywall.
Each unit in the duplex has two levels with 1,060 square feet of space and a 500-square-foot unfinished basement.
Pre-cast is common in commercial buildings and it’s a flexible medium that can also be configured to look like carved architectural details, such as cornices and window ledges.
Rodenburg said the structural strength of concrete allows for a green roof, although that wasn’t including on the prototype. The home can also be disassembled and reassemble on another lot, he said, making it recyclable and sustainable.
“Going NetZero was an afterthought really,” Rodenburg said, noting the project is applying for LEED (Leadership in Energy and Environmental Design) certification. “But then we realized everything was in place for it. They don’t even have a gas line going in because the solar system can provide enough power for cooking.” The homes will draw from the grid at night and during overcast days but supply the grid when the sun is shining with a Net Zero balance over a year.
The project is a one-off so it’s been an expensive undertaking but if it were to go into mass production — and Lafarge is thinking that way — costs would be competitive traditionally built homes. This version also has sensors to monitor energy efficiency and track the thermal mass of the structure for future learning.
Edmonton was chosen for it’s cold climate and proximity to a Lafarge plant.
There’s some interest in developing the concept for aboriginal housing, which is desperately needed in many areas. It could also provide robust, mould resistant and fast build housing for places like Attawapiskat, whose housing crisis made world headlines last year.
The concept came out of a conversation at a Canada Green Building Conference between Lafarge and Stantec delegates. The idea was to build one prototype in a cold climate and another in a hot climate. The second project has been delayed since Lafarge has since sold off its interests in Atlanta, Ga., but is scouting for another site.
For Alfred Nikolai, president and CEO of Habitat for Humanity in Edmonton, said it’s not about whether houses are built with concrete or wood, it’s about creating homes.
“The real story is that two families who really need homes will have them,” he said.