Daly City planning commission recommends zoning change to require on-site stormwater detention, exempts ADUs

The Daly City Planning Commission on June 3 voted to recommend that the City Council approve a zoning-text amendment that would require on-site stormwater detention and infiltration in addition to existing stormwater treatment requirements, while exempting accessory dwelling units (ADUs) and small additions.

Michael, the planning staff presenter, told the commission the draft ordinance would codify when detention — engineered on-site retention or infiltration systems — is required, and would convert prescriptive runoff coefficients that had been optional into mandatory standards. "This is a request by the city of Daly City to change the zoning ordinance to amend chapter 17 ... to require stormwater and infiltration in addition to stormwater treatment," Michael said during the staff presentation.

The commission and staff framed the proposal as aimed at clarifying local practice and reducing street flooding and erosion in Daly City’s hilly neighborhoods. Staff said the change complements the Municipal Regional Permit (MRP) and C.3 treatment requirements administered through the San Mateo County stormwater pollution-prevention program, but that detention requirements are the local code change before the commission.

Public commenters urged caution and asked the city to address several practical problems before the council acts. Andy Tan, a civil engineer who spoke in public comment, said the city has in some cases required detention on small projects without a clear legal basis and recommended the commission reject the draft if it would impose new burdens on small-lot construction. "I strongly recommend the commissioners to reject this ordinance," Andy Tan said, arguing the city previously lacked legal authority to impose detention on many small projects.

Ben Bermudez, an ADU owner, described a four-year permitting process for his 700-square-foot ADU and told the commission a retention system required on his project added more than $8,000 and delayed completion. "It took a huge amount of space in the back of the yard ... and it was something that, again, some people were required and some people were not," Bermudez said, calling enforcement inconsistent.

Contractor Fergus McHugh and other trade commenters described narrow Daly City lots, steep terrain and local soils that make large buried retention pits impractical on many parcels. McHugh urged staff to consider alternatives (pervious surfaces, bio-retention) and recommended applying any new requirement at the time of application rather than at permit issuance so builders and homeowners can include costs in financing.

Staff said the draft already proposes exemptions for attached/detached ADUs and small additions that create or replace less than 2,500 square feet of impervious surface; staff noted state ADU law restricts local regulation of ADU construction, and said the policy seeks to reduce burdens on small residential projects while clarifying requirements for larger development. The planner also said it is likely the ordinance will be written so it applies to new applications submitted after the ordinance takes effect, and that pending applications would not be retroactively subject to new detention requirements. Staff estimated the ordinance could take effect by the end of the summer after the city attorney prepares a draft ordinance for public review.

After hearing public comment and technical questions, a commissioner moved to recommend approval of the staff findings and the zoning change, including a CEQA review under Guidelines §15061. The commission approved the recommendation; the roll call recorded affirmative votes and one abstention. The commission’s recommendation will be forwarded to the City Council for final action and the city attorney’s office will circulate a draft ordinance for public comment before the council hearing.

Why it matters: Codifying detention rules would make local expectations explicit, potentially reducing future disputes over whether homeowners must install retention systems. Opponents said the measure could impose disproportionate costs and practical challenges on small‑lot projects unless exemptions and implementation timing are spelled out. The council will now review the staff draft and any recommended amendments.

The Planning Commission adjourned after the vote; an attendee closed the meeting with announcements about two upcoming community events.