Bloomfield Hills staff urge limiting driveway/walkway credits to protect open space and stormwater

City staff on Tuesday told the Bloomfield Hills City Commission that two longstanding exceptions in the city's landscape open-space ordinance allow driveways and decorative walkways to be counted as open space and, in practice, increase impervious surface on redeveloped lots.

"Open space is the pervious ground," said Amy, a city staff member who led the presentation, summarizing four years of project reviews. She said the staff team recalculated 25 residential projects from 2020 to 2024 both with and without those exceptions and found that in 18 of 25 cases removing the credits would have left the lot below its district minimum for open space.

The staff proposal would remove the driveway and walkway credits in single-family zoning districts that do not go through a site-plan review process (A1, A2, A3, A31 and A4), so driveways and decorative hardscape would be counted as hard surface rather than as open space. Amy said the change is intended to sustain the tree canopy, limit added impervious area and help manage stormwater in a city that lacks a large, centralized stormwater system.

Commissioners raised equity and practicality concerns. "If you take away that credit, I don't think my house is buildable," said a commissioner who noted long, curving driveways on many lots. Others called the walkway exception'which allows up to 30% of required landscape open space to be credited for walkways and decorative features'an apparent drafting error that can produce anomalous results on the city's largest lots.

Amy responded that the walkway credit is calculated as 30% of required open space rather than 30% of the house footprint, which can lead to a larger allowable hardscape area than was probably intended. She said applicants sometimes design to exploit the exception, citing an example in which applicants proposed a green roof on a sports court to reach a desired calculation.

After extended discussion, commissioners agreed to refer review of the walkway exception to the planning commission for a public hearing and recommendation. The commission also voted not to remove the driveway credit that evening and asked staff to collect empirical data over a one-year period on how the 30% walkway allowance is used and whether removing it would materially improve stormwater outcomes.

The staff presentation noted neighboring communities use different approaches; West Bloomfield and Birmingham, for example, do not grant similar exceptions but also regulate smaller minimum lot sizes. Amy said the goal of the proposed amendment was narrow: clarify what counts as green space and simplify administration so applicants and staff have fewer judgment calls about whether a surface is a driveway, walkway or patio.

Next steps: the commission limited the referral to a planning commission review of the walkway exception, asked staff to gather a year of additional data about how the exception is being used, and requested that planning commission conduct a public hearing and make a recommendation back to the city commission.