Keeping rainwater out of the basement

Thestar.com
May 10, 2021
Tracy Hanes

When Sinden Norton and James Bell bought a large 1908 home on Toronto’s High Park Blvd. in 2007, they had their work cut out to update it.

Over the years, they tackled one project at a time. One of the lingering issues was that when it rained, little “rivers” would run through the cold, damp basement. Their huge lot was covered by asphalt, which prevented stormwater from being absorbed into the ground.

“My big concern was the rainwater runoff and what to do with all that asphalt,” said Norton. Previous owners had installed new landscaping on top of the original hardscaping without proper grading, causing water to run into the basement windows. The couple had been upgrading the house’s energy efficiency, with new insulation and a geothermal heating system, and wanted a sustainable solution for their yard and driveway. When they had to dig a trench around the house to fix a leak in the geothermal system, the time was right to correct the flooding problems.

The amount of pavement in cities is a big and growing concern. According to the Toronto Region Conservation Authority, stormwater (the rainwater and melted snow that flows over roads, sidewalks, parking lots, lawns, driveways, etc.) picks up pesticides, road salt, oils and other pollutants as it runs into storm ditches and municipal sewers. The contaminant-carrying water is transported to rivers, streams and lakes and causes not only flooding, but erodes river banks, destroys aquatic habitat, creates sewer overflow and damages infrastructure.

The High Park home of Sinden Norton and James Bell was the first residential project in Toronto to use PurePave, a new Canadian-made technology that creates a surface allowing rainwater to seep into the soil rather than creating runoff.

Norton discovered a new paving material called PurePave at the National Home Show in Toronto. PurePave Technologies, based in Ottawa and founded by Taylor Davis, a permeable paving scientist with the National Research Council, uses a unique binding agent to create a surface that allows rainwater to seep into the soil, rather than creating runoff. It can handle a year’s worth of rainfall within an hour and is six times stronger than asphalt. Extensive NRC testing has shown that its surface is more elastic than asphalt and concrete and it can withstand the harsh freeze/thaw cycle of winter without cracking.

Davis said PurePave uses chunky, angular stones in its base that are large enough for water to filter through. Air pockets between the stones stay warmer than the surface, so snow tends to melt faster on PurePave and ice is less likely to form.

PurePave started out by doing commercial jobs, such as parking lots, then moved into the residential realm. The Norton-Bell 2019 job was its first residential project in Toronto and the result is net-zero runoff -- all stormwater remains on, and is absorbed by, the property.

“In big neighbourhoods, we can lower the stress on storm sewers, reduce size of storm management ponds and use the land for other purposes,” said Davis. “There are a bunch of cool advantages.”

Fusion landscaping, developed by York and Peel Regions with Landscape Ontario, combines softscape (plants), hardscape (permeable or otherwise) and rainwater elements (rain barrels).

Municipalities are becoming increasingly concerned about issues caused by stormwater runoff. Kitchener, Waterloo and Ottawa are implementing incentives including tax reductions or subsidies to encourage homeowners to reduce runoff. Toronto Water and the city’s department of Economic Development & Culture have been holding consultations on water fees, programs and measures to make the city’s water and sewer systems more resilient to climate change and to reduce flooding risk.

The annual costs of overflowing rivers and rising seas in Canada could nearly triple by 2030 if the country doesn’t do more to improve flood protection, according to the global think tank World Resources Institute.

“When you build up a city, you pave it,” explained Tony DiGiovanni, executive director of Landscape Ontario. “You forget the Earth is alive. It costs billions of dollars to put pipes in the ground and you’ve got all of this development -- policies that put more people in smaller areas and properties that are smaller and smaller. Where is the water going? It’s a huge issue.”

He said while the landscaping and horticultural industry has traditionally been driven by beauty, it also serves a highly functional purpose. Many regional and municipal governments plus conservation authorities in the province promote Low Impact Development (LID) which keeps water at source and slows runoff. Landscapers can facilitate that, DiGiovanni said, noting that Toronto’s green roof bylaw is one example.

LID has spawned programs such as the Fusion Landscape Professional Program, developed by Peel and York Regions with Landscape Ontario. Unlike zeroscaping, where gardens use little water but look “like weed patches,” said DiGiovanni, fusion landscaping combines softscape (plants), hardscape (permeable or otherwise) and rainwater elements (rain barrels). Homeowners can also create a rain garden where runoff from downspouts can be diverted to a garden of native plants, collected in rain barrels or directed with rain chains.

While PurePave is one of the newest products to reduce runoff, there are other solutions such as permeable pavers (such as Unilock’s) which use a grout that allows water to percolate through. George Brown College has installed Ecoraster black plastic grid in three parking lots filters water down through a gravel surface. Plants and trees are also excellent for recharging groundwater; trees act like vertical “rain gardens,” DiGiovanni said.

As the pandemic drives interest in gardening and landscaping, the time is right to promote more sustainable options that can reduce runoff, DiGiovanni said. “Municipalities and designers are starting to think about it because they have to. There are better ways to landscape.”

Rain chains are another solution to divert rainwater runoff away from downspouts and into a garden or a rain barrel.

The Norton-Bell house: Sinden Norton and James Bell ruled out using interlock at their High Park house because weeds would grow between the brick, said Norton. They worked with landscape firm Infinite Possibilities to design the PurePave colours (seashell pink and black) and a layout to fit with their brick pavers.

PurePave provided design, engineering and installation of permeable surfacing by implementing geotech and soil infiltration testing for permeable base engineering, permeable base construction and PurePave surfacing. An asphalt strip on part of the driveway remained to reduce some of the cost. PurePave was also used on the turnaround and front and side walkways.

Cement slabs were removed from the front steps and then PurePave installed to look like a rug. In the heavily shaded backyard, the couple went with a European courtyard-style yard. It incorporates glow stones in the PurePave surface that “look like the galaxy at night,” said Norton. The yard also includes Credit Valley stone as accents, a water feature and in the warmer months, container planters and hanging planters.

Because their house was the first Toronto residential project for PurePave, Norton said there were a few challenges, For example, a rainstorm during the 2019 installation caused the binding agent not to adhere properly, but Norton said PurePave’s customer service was excellent and the company resolved the issue.

The extensive landscaping and paving project cost $200,000 plus, said Norton. “There was so much work to do, so it was going to be expensive no matter what we did.” And PurePave has been 100 per cent effective in eliminating runoff, she reports.