County Low Residential Study

Arlington's "Low Residential Study" May Introduce Impervious Surface Limits in Less Dense Areas

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Arlington County is studying -- via its Low Residential Study or LRS -- whether to set a first-ever maximum allowance to limit the amount of Impervious Area (IA) on redeveloped properties in low residential zoned areas of the County (generally zoned as "R" and "RA"districts).  The study is also sometimes known as a "lot coverage" study.

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This is designed to address goals contained in the Forestry and Natural Resources Plan (FNRP), Chesapeake Bay Preservation Plan, and Stormwater Plans, all elements of the Comprehensive Plan that directs future growth.  The County hopes reducing IA will help control stormwater runoff that causes flooding, erosion, and poor water quality in the Bay and will help us achieve the FNRP 40% tree canopy goal.  (NOTE:  a canopy of approximately 50%-55 % in the "low [density] residential areas is needed to make up for low canopy cover in denser areas.)  

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What Problem is Solved Over What Timeframe?

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The County has long acknowledged major environmental threats from flooding and tree loss, with its last effort at reform in November 2005. As problems persisted, by December 2023 the County Board agreed - as part of the FNRP and backed by the Forestry and Natural Resources Commission, Arlington Tree Action Group and a combined group of diverse civic associations - to study existing standards for dimensional "lot coverage" that are now used to regulate how much land can be developed in these low density areas (more info below in "resources.")  These standards include: 

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• maximum building heights;

• maximum house footprint (which, together with height, limits limits the overall size of the house);

• minimum building setbacks from lot lines; and

• max. overall lot coverage (which includes the house footprint, driveways, detached buildings, pools, sidewalks, etc.)

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The FNRC recommended in Feb 2024 that the County present a "workplan . . .on reducing allowable lot coverage to provide room for planting trees. This is consistent with the recommendations in the recently updated Chesapeake Bay Ordinance, as well as the recently adopted Forestry and Natural Resources Plan." (see full letter in resources section below.) In November 2024, new findings on the tree canopy and flood risk showed problems were persisting and identified new home "footprints" on residential lots as the "elephant in the room" as key to solutions.  In early 2025 however, likely fearing major blowback from developers, the Board changed tack and directed staff NOT to study reduced footprints or zoning lot coverage, and instead to look at capping impervious areas or IA.  Initial study inputs were released in July 2026, and by September staff had laid out out suggestions for low, medium and impervious area maximums (as a percentage of minimum lot size in each R or RA zone).  See resources below for a link to proposed new guidelines. 

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ASF believes the Board should recommit to study and revise zoning dimensional standards, it is much easier for Arlingtonians to comprehend and engage on lot areas taken up by built structures, vs. impervious surfaces that are not easily tracked by the larger community of non experts.  Adopting IA maximums -- and possibly removing the zoning controls listed above -- is a step in the wrong direction.  Staff incomprehensibly is now proposing that EACH of three new IA caps would exceed the current median lot coverage for all lots in Arlington.  Staff has not yet demonstrated or quantified how or how soon new guidelines would slow tree loss and flooding, nor whether they would shrink home footprints or even reduce runoff. The incredibly dense study data (139 pages), the poor analytic approach and inability of the community to understand and engage on all new building standards lead us to believe the County's IA approach may well have no real effect on tree canopy or runoff.  See County's latest IA maximums for residential zones here.  As one example of the new proposed IA limits, the R-6 zone, which covers the largest percentage of all low-density residentially-zoned land, currently has a median IA coverage of 35%; the County is proposing new caps of 40%, 45% or 50% respectively. 

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What Does New Home Lot Coverage Look Like?

ASF Before and After Images

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Confirming county data that new home footprints are the main obstacle to our tree canopy, stormwater and Chesapeake Bay goals, ASF before and after images of lots where developers in the past 5 years have swapped out modest-sized homes for structures more than double the size.

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