INSIDE:
Storm water system passed test
Some Calgary condominium developments that included rain-shedding and water-handling features in their designs stayed nice and dry despite heavy rainfall that spurred historic levels of flooding last month in the city.
There’s overland flooding, such as that recently experienced by great swaths of Calgary when rivers overran their banks.
And then there’s the kind of damage that happens when basements or parking garages get wet because nearby surface water from rain has seeped through the ground into foundations.
With the kind of rain Calgary saw leading up to the great flood in June — 78.6 millimetres in two days — some homeowners were worried this water would enter their basements.
But two multi-family builders in Calgary had projects with design elements that helped keep structures dry from the heavy rains.
Avi Urban received a Calgary Award in June for environmental achievement. The honour was given for the company’s innovative storm water system at its Victoria Cross townhome development in Currie Barracks in the city’s southwest.
The storm water system collects rainwater and diverts it into channels between buildings.
The water then collects in an underground cistern, where it is filtered through various layers of material and finally absorbed into the earth without feeding into the city’s storm water system.
Catherine Loughlean is the chairwoman of the condo board for part of the Victoria Cross development, where she lives with her husband and five children.
“We have had no flooding,” says Loughlean.
“We have three buildings in our condo. Each building has a sump pump and the water is pumped away from our buildings toward the centre of our backyards, which is then carried off into our own drainage system. None of it actually goes back into the city water system.”
She was curious to see how it would fare through the heavy rains.
“This has been a fantastic test to see how this has worked,” says Loughlean.
Mike Bucci of Vancouverbased Bucci Development Ltd. says his buildings in Calgary — including Tribeca in Mission, Xenex on 12th Avenue and Next in Bridgeland — all came through the heavy rains dry.
Two design considerations contribute to keeping it that way: keeping water out of a parking structure, and using rainscreen technology to help the building dry out properly.
“We go to great lengths to make sure we have a dry parkade,” says Bucci, who is vice-president of development.
“All of our buildings are designed to accommodate a lot of sub-surface water movement. I know a lot of developers have the view that it’s OK for the walls to be damp from time to time. We go to quite a length to make sure that never happens.”
Bucci’s parkade entrances are raised two feet (61 centimetres) above sidewalks, providing a barrier to keep rainwater from flowing into the parkade, while also creating a sense of separation of public and private space.
“That would have helped a lot of buildings — two feet is a lot,” says Bucci, adding that higher entrances are not a definitive flood-prevention element that would keep out all overland river flooding such as what some parts of the city experienced.
Heavy rains can also raise the water table beneath a building, which is another way water can come in contact with foundations and cause leaking.
Bucci’s latest building, Ven, is planned for Sunnyside, an area with a high water table, says Bucci. The site is at the bottom of McHugh Bluff, where water runs down when it rains.
“Rather than just relying on the concrete (foundation), we’re going to oversize the excavation for Ven and take the shoring walls — the temporary walls — and make them out of solid concrete and drive them down deep, deep into the bedrock; way deeper than we would normally do.
“Those concrete shoring walls will form a permanent cut-off wall, which will allow all the water coming off the hillside to part around our site, rather than just relying on the usual damp-proof and waterproof of the parkade walls. We’ll have this extra layer to push the water away from the parkade.”
It will cost $800,000 to $900,000 more than a typical parkade structure due to this extra protection, he says.
Bucci Developments has brought its experience building on the rainy West Coast to Alberta, including rainscreening on its exteriors to help its buildings dry out after a rain, helping to prevent mould from growing.
“We come from a wet, tropical climate, basically,” says Bucci.
“We know that even in Calgary’s environment, you need a rainscreen assembly. Your rain, even though it doesn’t last as long, it hits so much harder.”
Rainscreening provides an airspace behind the exterior cladding. It provides a second drainage plane, so that any water that gets behind the siding — vinyl, stucco, or other — can still run down.
Secondly, it’s a drying mechanism, relying on the chimneyeffect of hot air rising and drawing air up through the space.
“There’s air constantly being pulled through that airspace that is drying out the building,” says Bucci.
“Even if you do get hit with a monsoon rainstorm, the problem with a face-seal system (with no airspace) is that the moisture just sits there until August, when it finally gets baked out of the building. With a rainscreen assembly, immediately the air flow gets going through there and drying out the building.”