Commission rejects request to exceed 55% impervious coverage for pool at 65 Aberdeen Place

The Clayton City Planning Commission on July 7 denied an applicant's request for additional impervious coverage related to a proposed pool and pool deck at 65 Aberdeen Place, finding the materials and mitigation presented did not meet the commission's threshold for "just cause."

Staff explained the property is zoned R-1 and the project proposes a pool and patio that would exceed the city's maximum permitted impervious coverage. The applicant sought relief under section 405.18.90(b), which allows the planning commission to grant additional impervious coverage when an applicant demonstrates just cause. Staff concluded the applicant had not demonstrated just cause and recommended the commission not approve additional coverage. The staff report noted differences between applicant and staff calculations of impervious area and raised concerns about the clarity and sufficiency of overflow management mechanisms.

Brian Beck, the applicant, presented extensive materials and engineering measures intended to mitigate runoff. Beck described six mitigation elements: grading and regrading to slow downhill flow, an underdrain system (perforated pipe under the decking leading to a sump pump), a large drywell sized to capture up to a 100-year, 60-minute event, a rain garden at the rear lot line, a pump to daylight to the front yard if the system overflows, and a rain barrel for reuse and runoff reduction. "I'm here to demonstrate just cause on behalf of my family," Beck told the commission, emphasizing that most of the impervious-area difference came from a proposed pool deck and from counting portions of an existing elevated wood deck as impervious under staff practice.

Beck argued the existing elevated wood deck should not be treated the same as decks at grade, saying the elevated deck is porous and that gravel beneath it permitted infiltration. He also said his drywell is substantially oversized compared with typical requirements, describing it as "500% more" capacity than the minimum he was asked to design for. Beck said he had worked with neighbors, removed a downspout at the neighbor's request, and hired an engineer after staff suggested more robust detention measures.

Commissioners probed technical details, raised enforcement and precedent concerns and questioned the long-term reliability of multi-component mitigation systems. Planning Commissioner Steve Lichtenfeld summarized the core concern: "My concern with any mitigation system is that all you have to have is one default in it, and it virtually destroys the mitigation," and said approving engineered workarounds risks creating a precedent the city cannot sustainably manage. Several commissioners suggested more limited options — smaller pool, less surrounding paving, or minor plan changes — that would keep the project within the 55 percent cap.

Staff and commissioners also discussed how the city counts impervious surfaces: the pool is counted as 50% impervious under current ordinance language; decks can be counted at 75% or 100% (the latter if covered); and pervious pavers have historically been treated as impervious for the city's calculations. Commissioners noted some of the applicant's disagreement with staff calculations narrowed the numeric overage to a relatively small amount (estimates discussed ranged from roughly 49 to 80 square feet over 55 percent), but they said that did not resolve the broader question of setting precedent.

After discussion the commission considered motions. The staff recommendation was to deny the request for additional coverage. A motion to approve the application to exceed 55 percent was made, seconded, and failed; the practical result is that the applicant's previously approved permit that fits within the city's limits remains valid, but the revised plan seeking additional coverage was not approved.

The commission did not adopt special conditions or an approval that would allow the larger pool deck; the applicant was informed that the permit he already holds for a plan that meets the coverage limit remains valid and could proceed.