Riverside has changed its village code to encourage the use of semi-pervious surfaces on residential lots over impervious surfaces by allowing residents to use up to 20% more of the semi-pervious material.
With village trustees’ unanimous passage of an ordinance March 6, semi-pervious surfaces are now defined as those that allow stormwater to pass through them into the ground below, including permeable pavers, porous concrete and pea gravel. Trustee Aberdeen Marsh-Ozga was absent at the meeting and did not vote.
Village Planner Anne Cyran told the village board that these surfaces must be installed properly so the underlaying soil retains at least one inch of stormwater to count as semi-pervious under the revised code.
The ordinance defines impervious surfaces as those like roofs, concrete, asphalt, bricks, compacted gravel or any structures like pools or water features that would not allow stormwater to seep beneath them and absorb into the ground.
To encourage residents to use semi-pervious surfaces rather than impervious ones, which would allow Riverside to better manage its stormwater from rain or overflow from the Des Plaines River, semi-pervious surface coverage will be determined with a “20% discount rate,” Cyran said. That means an impervious surface with an area of 100 square feet, for example, would be considered equivalent to a semi-pervious surface with an area of 125 square feet when calculating how much of a lot is covered.
Under the new definitions, newly laid pervious surfaces like permeable pavers that were previously considered at a 100% discount rate — meaning they weren’t counted at all toward the total amount of surface coverage — will be considered semi-pervious.
“Permeability [of semi-pervious surfaces] decreases over time as the voids get filled with organic matter. We can’t assume that the surfaces will be cleaned and maintained, especially as property changes hands over the years,” Cyran said. “We have to assume there’s going to be some level of decrease in permeability over time.”
Village President Doug Pollock clarified that permeable pavers and similar surfaces that had already been installed would be grandfathered in, so the new definitions will only apply to newly laid surfaces.
“Right now, under our current ordinance, if you put in permeable pavers, and they’re done right with the underneath drainage and all that, they’re treated the same as grass, so right now, it’s 100% [discount rate],” he said. “There’s language in there that says, if you have permeable pavers now, they will continue to be treated as 100% permeable.”
Cyran said the 20% discount rate, which allows about 7% more hardscape on lots if all the impervious surfaces were to be replaced with semi-pervious surfaces, was recommended by Riverside’s planning and zoning commission when they reviewed the standards at a public hearing in December.
“They reached this recommendation after considering what different discount rates would look like on an average property if all of the hardscape was replaced with semi-pervious surface,” she said. “They determined that this created a good balance between incentivizing the installation of semi-pervious surfaces while ensuring the lots with more semi-pervious hardscape still look like they fit in the character of Riverside.”
At the meeting, trustees Jill Mateo and Megan Claucherty expressed concern that residents might forgo semi-pervious surfaces altogether due to the reduced amount of coverage now allowed by the village code.
“People may throw their hands up and say it’s just not worth it [to use semi-pervious surfaces] for a modest gain,” Claucherty said. “That would be the risk: that people opt for a smaller amount of hardscape instead of slightly more semi-permeable surface.”
Pollock said the planning and zoning commission was likely recommending the change to limit the total amount of hardscape on properties in town.
Despite their worries, the trustees agreed to approve the ordinance and see how it affects hardscape coverage in Riverside.
