By Mark Douglas Wessel

The Advance of Permeable Surfaces

In 2010, flood damage in urban areas, including homes, businesses and public infrastructure in Canada, registered at approximately $3 billion according to the World Resources Institute. And if nothing is done to address this problem, the think tank estimates that by 2030 those costs could balloon to over $8 billion. 

Ask a planner, an environmentalist or someone working in a municipal road, water or sewer department and they’ll point to hard, impermeable surfaces—particularly roads and driveways—as key contributors to urban flooding.

To put things into perspective, Craig Reid, senior advisor for the Association of Municipalities Ontario, says that AMO members continue to be pro-development, with a particular interest in more affordable housing. “But they’re also trying to manage externalities. And a major piece of that is flooding and runoff.”

Reid says that after years of steady urban growth, many municipalities must now contend with the fact that a heavy concentration of roads, roofs, driveways and hardscapes convey water runoff far faster than natural surfaces. Consequently, “in places like Burlington, Toronto and Peterborough, we’re seeing these really fast, intense storms that are overwhelming the local stormwater management and, in many instances, water is backing up into people’s homes.”

Despite this new reality, instead of singling out residential homeowners or builders as simply being part of the problem, some city officials are now increasingly reaching out to these groups to be part of the solution, as is the case with the City of Kitchener. 

“We’re a groundwater-dependent community. So we’re trying to encourage developers and home builders to maintain the natural hydrological cycle to the maximum extent possible,” says Nick Gollan, manager of planning and programs for Kitchener’s sanitary and stormwater utilities. 

By “encourage,” Gollan refers to the fact that Kitchener is offering up to a 45% reduction in the stormwater portion of a monthly utility bill, tied to such homefront improvements as installing rain barrels, rain gardens or permeable paving—work that can be done on existing homes or in new residential projects. 

According to RAIN, a community-based group that works with municipalities and homeowners to reduce runoff and manage rain where it falls, the success of the stormwater credit program has resulted in diverting more than 500,000 m3 of rainwater from Kitchener’s sewer system per year.  

Despite this success, Gollan estimates the city still incurs $15 million annually in costs associated with water runoff. “You can easily spend $3 million to $5 million (per location) to fix damage to water courses and nearby infrastructure,” he notes. 

Apart from incentives to reduce water runoff, as home builders are well aware, hard-surface restrictions are all too common for new residential communities, especially in areas that are designated as environmentally sensitive. 

Leor Pomeranc, whose Ontario numbered company specializes in building upscale rental apartments, says the Town of Perth mandated the use of permeable paving solutions for a project he completed in 2019. “Otherwise we would have exceeded our impermeable lot coverage ratio and would have had to drop the number of homes from 27 to 25.”

In order to prevent that from happening, which would have significantly cut into his profit margin, Pomeranc turned to two permeable paving solution providers. The first was Ottawa-based PurePave Technologies, which has developed a highly porous surface—capable of absorbing 14,000 litres per cubic metre per hour—that’s comprised of natural aggregate with a polymer bonding agent and permeable base system. The second company was Toronto-based LID Paving, distributor of the Ecoraster permeable paving system that deploys gravel or grass in plastic grids. 

For the Perth site, Ecoraster was used for some of the residential driving lanes, while PurePave was installed on the walkway and vehicle parking pads. 

In hindsight, says Pomeranc, “It was a no-brainer for the project,” not only from a profitability standpoint, but also in terms of how the company is now perceived. As a luxury rental home builder, Pomeranc indicates that his company “invests hundreds of thousands of dollars into landscaping for each project, and PurePave surfacing adds to that image” thanks to the product’s stone aggregate finish.

“It’s also nice to be able to say that we’ve done a low-impact development (where stormwater runoff is managed as part of green infrastructure).”

One of the pioneers of aggregate, resin-bound surfaces is Addagrip, a UK company that launched its product back in the 1980s. Notwithstanding its environmental benefits in terms of porosity and water control, managing director Roger Critchley readily admits that Addagrip’s primary motivator in the early days was “coming up with an attractive surface for parks and schools that was a faster product to put down.” 

Critchley says their surface also addresses planner concerns over “not wanting to have too much black surface on the ground,” both in respect to aesthetics and concerns over high concentrations of hot surfaces during the summertime that contribute to the heat sink phenomenon. It is also ideal for nursing homes—and, for that matter, all residential settings, he notes—because of the product’s slip-resistant surface and the fact that their driveways, walkways and patios “help to get the rain into the ground as quickly as possible.”

Everyone from builders to landscape architects in the UK have fast-tracked employing Addagrip’s product on the residential front. Initially it was mostly for high-end homes, but increasingly the surface is being used for mid-range residences as well. “Quite often they want to use our product because the driveway is the first thing you see,” and that can be a significant selling point, Critchley notes. 

The company has become so mainstream that “every major town in the UK has an installer,” says Critchley, who notes that economies of scale and speed of adoption has helped lower the cost of the product over the years.

Harsh Realities

The initial cost, however, remains the obvious drawback for builders and developers: Whereas the average cost to pave a 400 sq. ft. new home driveway with asphalt is around $1,800, it’s closer to $10,500 for PurePave (although there are volume discounts beyond 1,000 square feet, the company notes.)

But there are other factors to consider. From a property-owner maintenance standpoint, PurePave surfaces resist ice build-up, and snow melts 50% faster. Further, concrete and asphalt require touch-ups every few years and are more prone to buckling due to freeze/thaws cycles. Asphalt also has a particularly short lifespan. Interlocking brick, meanwhile, takes longer to install and can also be prone to heaving over the years if not installed properly.

Permeable surfaces require some maintenance as well—ideally an annual pressure wash at the bottom end of a driveway where cars enter, as some clogging of the openings can occur, although not enough to affect the ability of the overall surface to absorb/retain water.

While Addagrip has excelled in the UK and has caught on to some extent in the southern U.S., it never made it to Canada—in part because the product couldn’t withstand the harsh freeze and thaws that are all too common here. 

Inspired by Addagrip’s success but also cognizant of Canada’s weather obstacles is what ultimately compelled PurePave Technologies CEO Taylor Davis to work with some of Canada’s top construction materials chemists to develop a polymer/aggregate surface that is not only highly porous but was made specifically to withstand our climate. 

To verify these capabilities, the University of Ottawa recently conducted rigorous freeze-thaw tests in which several PurePave samples were filled with water and placed in a freezer at -40°C for an hour, before transferring them into an isolated room with a temperature of 30°C for an hour. The finding determined that the surfaces retained a flexural strength of 6.1 MPa (62.2 kg/cm²)—six times that of asphalt at room temperature. 

It was the first time the university had tested a surface in this manner, where no degradation in flexural strength was identified.

Reassured by those performance numbers, Markham-based builder Flato Developments Inc. eyed the product for its Palgrave Estates community in Caledon. Not unlike Pomeranc’s Perth project, Flato must adhere to municipal water runoff restrictions. 

“We’re now in our fifth year of getting the site developed, and the agreements with the town are that the driveways have to be finished with permeable pavers,” observes senior project manager Dan Lacroix. “It’s in Caledon’s urban guidelines for estate developments to have this (type of surface).”

As of February, Lacroix indicated they’re currently in discussions with Caledon to determine whether they’ll be required to make all of the driveways permeable, just a portion of the driveways or, possibly in lieu of permeable driveways, a permeable surface in front of the garages. 

Lacroix says that Flato will cover the cost of any permeable paving adjacent to the homes, while the cost of any driveway permeable paving will be borne by the homeowner. 

Caledon’s director of engineering Andrew Pearce helps provide a snapshot of how he and his peers perceive the growing challenges of water runoff. “The town will use green infrastructure while managing rainfall at the individual lot/house level, along its path of flow and before it enters a body of water. This includes: the use of permeable pavers (as has been done in the Flato development); bio-retention cells (landscaped depressions that capture stormwater); soakaway pits (larger holes filled with coarse stones used to capture water from drainage pipes); and perforated pipe systems to manage stormwater, which collectively will help meet multiple stormwater objectives,” Pearce explains. It’s all part of “necessary actions to building a sustainable Caledon.”

Against that backdrop, Lacroix says PurePave’s porosity and durability was one draw. Another was the appearance of the surface, as well as its non-slippery nature—even when wet. 

As far as upgrades go, “homeowners are still thinking about kitchens and bathrooms,” accepts Lacroix, although he’s confident permeable paving products could catch on. 

Mindsets are constantly evolving, he notes. When he was first starting out 30 years ago, one builder Lacroix worked for decided to install nine-foot ceilings. “Everyone thought he was crazy for doing that. And sure enough, now we’re doing 10-foot ceilings everywhere. So there’s always room for creative outcomes.”

Residual Cost Savings

In the case of the Flato development, PurePave’s Davis says there’s an opportunity to “transform the whole neighbourhood into a net-zero runoff site while increasing curb appeal. The only runoff going down the street would be just from the street surface and not the homeowner properties”—the net effect being greater protection for the local watershed. 

While some builders may be dissuaded by the product costs associated with achieving such a benefit, there are also residual savings builders can realize by incorporating permeable paving into their development on a larger scale. So says Craig Applegath, a founding partner of the Toronto studio of Dialog, a multidisciplinary architecture, engineering, planning and urban design firm. 

“A more porous site could be eligible for a higher-density, potentially more profitable development.”

“Where there’s an opportunity to reduce development costs is parking areas, especially multi-unit residential projects, where having a stormwater retention pond on site is expensive,” Applegath says. “So if you can use permeable paving (for the parking surfaces), it will allow you to use more site area.”

Getting even more adventurous, Applegath notes, “If you did permeable paving on both the driveways and the roads, then the whole stormwater situation basically is handled in the area in which (the storm) is occurring.” In doing so, the higher cost of permeable paving could easily be offset by the fact that a more porous site could also be eligible for a higher-density, potentially more profitable development.  

“If we want density, we can’t have these giant sites with huge retention ponds,” Applegath says. “So you have to figure out how to plan your site so that all of it is absorbing water.”

In keeping with that mindset, Ellise Gasner, CEO of LID Paving, says the Ecoraster product is often used in a residential setting “if you want to increase the size of your driveway, and your zoning doesn’t allow for any more solid surfacing. So in that instance it’s used more as a driveway extension.” 

From a community-wide perspective, Gasner says their product is commonly employed for access roads in and around stormwater ponds.

“Realistically, all of these ponds have access roads for (service vehicles) and Ecoraster can be used as a grass-filled permeable surface that blends in with the surroundings but can still support heavy vehicles when the road needs to be used.”

Similarly, PurePave contends its product can handle a 40,000 lb. loader driving overtop.

The Incentive to Change

From a cost perspective, some cities are looking to incentivize and accelerate the transition to more permeable surfaces. The City of Ottawa has announced a rebate of up to $5,000 for homeowners to install a permeable driveway versus a hard-surface one. And building on their current 45% stormwater fee discount incentive, the City of Kitchener is investigating a similar program as part of market incentives geared for “service providers,” including builders, landscape architects and driveway paving companies. 

Under newly proposed guidelines, the City of Kitchener would put into place an incentive whereby a provider would supply two quotes: one for a paved driveway and one for a permeable paved driveway,” Gollan explains. “So what we want to do here is create a level playing field. And given that the cost to install a permeable paver driveway is higher than simply paving it in asphalt, the City might pay for some or all of that difference in order to realize the environmental benefit that comes with reduced runoff.”

In many respects, Kitchener, not unlike other cities across the country, is dealing with a mindset that dates back to the 1800s, when “the primary focus was to get nuisance water away” from where homes were built, Gollan says. “We’ve inherited the impact of that decision-making, and what we’re trying to do now is reverse it. But we still have a long way to go.”

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