Riverside amends zoning rules to define semi‑pervious surfaces and sets 20% discount rate

The Village of Riverside Board of Trustees on March 6 approved text amendments to Title 10 of the village code that clarify surface‑coverage standards and create a framework for categorizing and measuring semi‑pervious (semi‑permeable) surfaces.

Planner Landers Siren summarized the changes: the amendments define semipervious surfaces operationally as materials that retain the first inch of stormwater and establish a discount rate of 20 percent for semipervious coverage when calculating impervious coverage limits. The Planning and Zoning Commission recommended the 20 percent discount after reviewing examples and visual impacts on typical residential lots.

Siren and staff said the change is intended to create consistent standards across varying soil types and to account for expected reductions in permeability over time if surfaces are not maintained. To qualify for the semipervious calculation, an engineer must confirm the surface design and on-site inspections would verify installation. Staff estimated the additional engineering review and two required field inspections would add about $375 to the permit cost.

Trustees debated the discount rate; some said they were concerned that reducing the credit from existing local practice (where permeable pavers sometimes counted at 100 percent) could discourage adoption. Nevertheless, trustees approved the ordinance as drafted and gave staff direction to explore a financial incentive to encourage replacement of impervious surfaces with properly installed semipervious materials. One suggested option would be to make such projects eligible for the village’s existing stormwater permit incentive program, which offers a one‑time refund of up to $250 in building permit fees.

Staff will return with recommendations on potential incentives and any adjustments to permit fees or inspection processes needed to implement the new standards.