Staff outlines impervious-area limit options to curb runoff and protect trees in Arlington

Arlington County staff on July 15 presented draft findings and public-engagement options from the Low Residential Study, a multi-phase effort to evaluate zoning amendments that would limit impervious surface on low-density residential lots to reduce stormwater runoff and support tree canopy goals.

Nick Rogers, co-project manager in the county’s Community Planning, Housing and Development division, told the Long Range Planning Committee staff had used stormwater utility impervious-area data, tree-canopy mapping and consultant hydraulic models to test the environmental effects of increased impervious area. “The models have confirmed several of our assumptions,” Rogers said, adding that water quality and runoff worsen as impervious area increases and that tree canopy helps but “it’s not a one‑source solution.”

The presentation made clear there is no staff draft zoning ordinance yet and no formal recommendation; the study is in phase 2, the public-facing portion. Staff proposed presenting three option bands (described to the public as lower, middle and upper limits) for standard-size lots in each zoning district and lot-size band. For single-family and traditional two‑family dwelling types staff said it would test example limits such as 50%, 55% and 60% impervious area to gather feedback; staff also produced visual diagrams of R‑5, R‑6, R‑10 and R‑27 lot templates to show what each percentage would mean in practice.

Rogers stressed trade-offs. Staff highlighted roughly 17,847 R‑6 one‑family lots in the LRS study area and noted nearly 4,000 lots are undersized for their zoning and legally nonconforming. On very small lots, a percentage limit can be inflexible; on very large lots it can allow substantial hardscape while still complying with a percentage cap. To address that, staff proposed treating undersized lots as if they were standard size to avoid undue inflexibility, and placing an absolute cap for oversized lots so large parcels do not receive an implicit incentive to add excessive impervious area.

The briefing also summarized a board-requested set of policy questions staff will test in phase‑2 engagement: whether existing lot‑coverage standards should remain alongside any new impervious‑area limit (staff said lot‑coverage requirements would not automatically be removed), whether to adopt a minimum contiguous plantable‑area requirement (staff’s preliminary recommendation was not to adopt one), whether yard or setback standards should be adjusted (staff recommended not to do so countywide at this time), and whether limits should be based on zoning district, lot size, or a hybrid approach (staff favored a hybrid of zoning district + lot‑size bands).

Public commenters and some commissioners pushed back on whether staff options would meaningfully reduce building footprints or curb market pressures that have favored larger replacements on tear‑down lots. A representative speaking for the Arlington Civic Federation cited the federation’s June 9, 2026 resolution and its vote in favor of broader lot‑coverage and setback reform; the speaker noted that vote on the federation resolution was "46 yay, 0 nay, and 1 abstention." Another commenter representing 27 civic associations said the staff options appeared “above the median impervious surface of existing lots” and asked for stronger analysis tying limits to building‑footprint outcomes.

Commissioners asked for clearer materials for public engagement (visuals and plain‑language examples), urged staff to explain where the analysis did and did not address heat‑island effects, and debated whether lot‑size‑only rules would be simpler and more transparent than zoning‑district approaches. Staff acknowledged the modeling did not quantify urban‑heat mitigation in this memo and said climate/heat work would be handled in parallel analyses.

Rogers said staff will pursue many engagement venues through October — including farmers‑market pop‑ups, library events, an online feedback form, and targeted industry focus groups (architects, engineers, contractors) — and expects to return to the planning commission in October–November with phase‑2 findings and a recommended approach to present to the County Board ahead of ordinance drafting.

The committee did not take formal action; the meeting was a staff briefing and public comment hearing to inform the next round of outreach and refinements. Staff noted a forthcoming technical memo with additional model results.

Clarifying details recorded at the briefing included staff’s use of the county stormwater utility data to compute lot‑level impervious area, the example test bands (50/55/60%) suggested for community feedback on single‑family and traditional two‑family dwellings, staff’s preliminary recommendation against a mandatory minimum contiguous plantable area (citing statutory authority limits), and the proposal to treat undersized lots as standard size for equity reasons.

Staff will incorporate public feedback and return to the planning commission this fall; any ordinance changes would follow a separate drafting and adoption process (ZOCO/RTA and County Board review).