How Will Arlington County Zoning Effect Your Project?

The Zoning Ordinance (AZO) regulates the size, location, and height of new homes and additions, and even whether a new house can be built at all. A ‘buildable’ lot conforms to current AZO minimum square footage, average width, and street frontage requirements. If your lot meets the current minimums, you are able to build a new home or addition. If a lot does not meet the minimums it is considered ‘non-buildable’. New homes are forbidden on non-buildable lots but additions are permitted if they conform to the current AZO. There is, however, one loophole: if a non-conforming lot’s deed was recorded prior to July 1950, then it is considered ‘grandfathered’ and new construction is allowed.

The AZO regulates building size via house footprint and lot coverage. The house footprint includes the house itself, roofed porches, attached garages, and taller decks. Each Zoning District has different maximum house footprint ratios (percentage of the lot area). Each District also has a different maximum house footprint cap (square feet). The proposed house cannot exceed either the ratio or the cap. Lot coverage includes the house footprint PLUS the driveway and any accessory structures (i.e. detached garages). Each District has a maximum lot coverage ratio (percentage of the lot area). Because the County wants to promote traditional residential streetscapes, the AZO gives ‘bonus’ coverage for both the house footprint and lot coverage if homes include front porches and/or detached garages.
The location of new structures and additions is governed by ‘setbacks’ which are minimum distances from the property lines. For all residential Districts the front and rear setbacks are 25’. Each District has minimum side yard setbacks. Several encroachments are allowed into the setbacks for things like porches, window wells, & accessory structures.

The final piece of the AZO puzzle is the 35’ height limit in residential districts. This is the measurement from average grade to roof midpoint height. Average grade is the mean elevation of the land abutting the structure. Both existing and proposed grades must be measured. The roof midpoint is measured (vertically) between the peak and soffit of the main roof – not the peak of the roof as commonly assumed.