Have you ever stopped to think of what happens to the water running off your house and onto your driveway when it rains?
If your home is like most, the water probably travels down gutters, through downspouts and onto an asphalt driveway, picking up traces of pollutants such as petroleum and pesticides along the way. Down a street gutter it goes, eventually finding its way into a storm drain.
This may be as far as you can visibly follow the journey, but it doesn’t stop there. Much stormwater runoff finds its way into nearby rivers and lakes.
Redirecting stormwater into the ground is a much greener option. Microorganisms in the soil are able to digest the pollutants, purifying the water on its path back into the aquifer. Allowing the water to seep into the ground also helps prevent the erosion of nearby waterways by runoff.
By replacing your impervious asphalt or concrete driveway with a permeable surface, you’ll be supporting groundwater recharge while also visually softening your property.
The first step in installing a permeable driveway (sometimes referred to as a sustainable drainage system) is deciding which design will work best for you.
Open-cell pavers are simply concrete pavers with holes that can be filled with a previous material. Filling the cells with vegetation can soften the entire look and add a bit of green to your site.
What’s underneath the pavers is what really counts. A solid base is key to minimizing heaving and cracking. You will need a six-inch sub-base of 1½-inch clean rock topped with a four-inch base of ¾-inch clean rock, to make the driveway stable enough for cars to pass over it. The paver system goes on top of that. A polyurethane liner should be used near any foundation walls or concrete that needs to be protected from water flow-back.
Pervious pavers commonly have joints filled with aggregate to allow water to penetrate between the pavers. Tabs are formed into each paver, providing the correct joint width and making installation easier. As with open-cell pavers, a sturdy base is required.
Some ceramic pavers are porous themselves, allowing the water to pass through the surface directly, instead of through the gaps between. This means the gap can be narrower and doesn’t have to be refilled with aggregate as often — a common chore with other pervious paver systems. Due to the small size of the pavers, cracking or heaving is not an issue in cold climates.
Although in our climate with snow needing to be plowed, another option is a gravel driveway. It will also need a base underlayment to maximize its pervious nature. Usually this is a plastic mat made up of circular or honeycomb cells structured to provide load-bearing support. These cells are filled with gravel and help keep rainwater in the soil and out of sewers.
One consideration is the type of soil you have. It could range from sand (fast drainage time) to clay (longer drainage time).
The best time to do a project like this is late spring or summer, when the weather will co-operate. Construction during winter in colder climates is not recommended due to frost-depth issues.
By installing a permeable driveway, you’ll be directly protecting the integrity of our natural resources, supporting groundwater recharge and adding green space to help balance carbon dioxide levels.
Sue Wastell is the President of the London Home Builders’ Association and Owner of Wastell Homes in London.