Rane Wardwell and the rest of the crew from Collective Carpentry in Invermere pulled into Rossland on a Sunday, and started pulling together the frame for a house the next day. By day’s end on Friday, the frame of the house was not only completely assembled, but tested well below the airtightness limits required for a Passive House.
A Passive House is a house that requires up to 90 percent less energy than a standard built house. The term earns capitalized letters because a true Passive House is certified — by the Canadian Passive House Institute in this case — and meets fixed criteria.
One of these is a pressurized test result of 0.6 ACH (air changes per hour) or lower. Post frame-installation, Wardwell and his team test the Rossland Passive House and get a result of 0.19 ACH.
The reason they were able to get the house assembled so quickly is because the walls were prefabricated at the Collective Carpentry shop in Invermere.
Jan Pratschke, the company’s designer, worked from the designer’s drawings to create shop drawings for the wall, floor and roof panels. Once completed, Pratschke’s drawing’s were shown both to the registered building designer and the general contractor to avoid any mistakes.
“Once we fabricate one of these panels, it’s really hard to change it,” explains Wardwell. “It’s a fully closed panel; it’s weather-tight on the outside, and it’s fully airsealed on the inside.”
The panels can be built to a maximum length of 20 feet; any longer and it would be too difficult to transport them. Walls are generally a standard height of eight to ten feet, and in this case, they’re extremely thick, about double the usual wall thickness at twelve inches.
Once the panels were transported to Rossland, the Collective Carpentry team worked with a crane to assemble the frame on top of the foundation, which had already been built by a team from Seven Summits Contracting, led by contractor Dan Eheler.
Keeping it tight
The challenge for Eheler going forward is to maintain the house’s airtightness.
“The next blower door test is a lot more difficult because of the … electrical and all your solar … all your penetrations in your exterior envelope,” he says.
The walls, already twelve inches thick, will have an additional six-inch interior layer, housing most of the houses pipes and wires, but at some point water, electrical, and sewage will need to breach the house’s airtight barrier to connect it to the outside world.
Doors and windows also need to be installed carefully. The windows for the Rossland Passive House have been imported from Austria.
“The Europeans are way ahead of us on their technology for building supplies, so a lot of materials on this project are European,” explains Eheler.
The house’s designer, Brett Sichello, is hoping that in the end the house will test somewhere between 0.3 and 0.4 ACH.
One of the goal of the Passive House standard is to minimize energy use, and the purpose of keeping the house airtight is to minimize the amount of heat transfer between the house and the outside, whether that means keeping the house cool in the summer or warm in the winter. That way energy isn’t needed to maintain a comfortable temperature inside the house.
But keeping the house airtight isn’t the only consideration. The windows in particular play a bigger part than simply breaching the envelope. The surface of the glass also allows for the transfer of heat between the inside and outside of the house.
The extent to which windows allow heat transfer is measured by their U-value. The lower the windows U-value, the less it allows heat to transfer through it.
“To meet BC Building Code, the window’s performance value is [1.8 W/m2k], and that’s the Uvalue,” explains Sichello. “Whereas the maximum installed value of a Passive House window is [0.85 W/m2k]. So it’s over at least double the performance.”
The house’s orientation also plays into the design of the house, and the type of glass used on any given side.
“On the north and east sides where we’re actually losing energy, we have a different type of glass, … its got a [lower] U-value, so it actually performs a bit better,” says Sichello. “Whereas on the south and the west where we have high solar heat gain, that glass is more transparent, and it allows more of that free energy from the sun to penetrate into the house.”
If everything comes together and the team can reach the goal of 0.3 ACH, Sichello estimates the total energy bill should be around $160 per year, plus or minus ten percent.
That number could be even lower, given that the house will have solar panels.
The house’s owners (who’ve asked not to be identified) chose to build passive given rising energy costs, but they had other requirements as well.
They specifically asked for a foam-free house. Foam has a high embodied energy — the energy it takes to manufacture something, and then break it down again once it needs to be disposed of. Foam is also an off-gassing material, and the owners wanted to avoid those as well, requesting as many natural materials as possible.
Unfortunately foam couldn’t be entirely avoided, as some of the alternatives were too costly, but the only places in the house with foam are the doors in the outside stairwell and the garage door.
The panels designed at Collective Carpentry are insulated with densepack cellulose insolation, which is made from recycled newspapers, and none of the glues used contain formaldehyde, which is toxic.
The solar panels will not only provide extra energy, but will also be attached to the side of the house, acting as a shade over the south-facing windows.
The owners also want to house rainwater for the garden, and plan to install a drain heat recovery system. The system uses the heat from water going down the drain to help heat water coming up through the pipes, and can be purchased for as little as $505 depending on the size.
The owners estimate that the house will cost them 15 per cent more than a standard house, but point out that as energy costs rise, the extra cost will pay off.