Check existing spaces first
Arlington County’s ADU guidance says existing parking spaces must be maintained in the corresponding number. If a lot has no space, the page describes a path to create one or use a Department of Environmental Services (DES) parking study when block occupancy is below 65 percent. At 65 percent or more, the guidance says at least one space is required.
The threshold depends on the County’s block-occupancy assessment, not a homeowner’s visual estimate of nearby parking. Ask the County how it defines the block, how occupancy is measured, what documentation the study needs, and which current process applies to the property. Do not assume that a study request guarantees an exemption or that a lower observed occupancy establishes eligibility.
Keep the parking result separate from access approval
Show the existing spaces and proposed layout on a site plan, and confirm whether construction removes any required space. Then review driveway legality, emergency route, and other permit or trade requirements independently. A parking study does not approve a driveway or fire-access route.
Use the County’s current guidance and zoning provisions for the application date. Save the block result and written County response with the project record; this page does not determine a particular lot’s occupancy or permit result. For a cross-jurisdiction rule-finding checklist, see ADU parking requirements and waivers.