Olivette commission approves 696‑sq‑ft detached garage at 9 Beechmont amid resident stormwater worries

The Olivette Planning and Community Design Commission voted to approve a site‑plan and community‑design petition for a 696‑square‑foot detached garage at 9 Beechmont Court on Sept. 19, subject to the staff conditions included in the Department of Planning and Community Development memorandum dated 09/19/2024. The motion was made by Commissioner Sam Wachter and seconded by Tim Spiegel Glass; the vote was recorded as five approvals and one abstention and the motion passed.

Staff told the commission that the accessory structure exceeds the 15‑foot administrative height limit, which is why the petition required commission review. Elevations shown to the commission listed a 21.4‑foot measurement on the front face and a higher rear measurement (staff noted the rear top‑of‑foundation as 25.4 feet). The proposal also includes a small driveway addition (43 square feet) and removal of an existing shed to keep accessory coverage within the city's 10% maximum.

Civil engineer Mark Kilgore presented the site’s stormwater calculations and mitigation plan. He said the parcel’s existing imperviousness would rise from about 27.2% to 28.4% and that differential runoff between existing and proposed conditions is 0.014 cubic feet per second (CFS), well below the Missouri MSD threshold that typically triggers detention requirements at 2 CFS. "That is a differential of only 0.014 CFS... This is really almost nothing," Kilgore told the commission. Kilgore said the proposed flow‑well chamber provides nearly twice the volume required by the project’s MSD‑based 20‑minute storm calculation (required 16.8 cubic feet; proposed storage ~28.68 cubic feet). He described the flow well as roughly 5½ feet deep with a level spreader approximately 8 feet wide designed to encourage sheet flow rather than a concentrated point discharge.

Several nearby residents urged caution. Michael White, who said he lives at 23 Ramsgate Drive and built a small backyard library, told the commission he is concerned that overflow could reach that structure: "Is it going to come into my library? That's the question." Gary Herman, who said he has lived on Ramsgate Drive for 28 years, described recurring water problems and said he worries cumulative construction uphill has increased flow to his property. Residents also noted a known undersized storm system in the neighborhood and asked whether larger, system‑level fixes by MSD or the city are planned; staff said options such as upsizing pipes are costly and would be considered by council separately.

Commissioners debated the cumulative effect of incremental approvals — calling it a possible "death by a thousand cuts" — but several members said the site‑specific calculations and the proposed mitigation likely improve the existing condition if constructed and maintained correctly. Staff and the engineer confirmed the project does not propose regrading to change drainage direction and that standard silt fences will be required during construction. The petitioner stated the detached garage will not replace the home's internal garage and that the higher roofline is intended to match the residence and provide interior clearance for a vehicle lift.

The commission approved the petition with the staff‑recommended conditions. Next steps are final plan verification and building permits, and staff noted routine maintenance (periodic inspection and vacuum removal of sediment from the flow well) will be the property owner's responsibility.