R-20 One-family Dwelling District Setback and Placement Standards

In the R-20 One-family Dwelling district of Arlington County, primary residential structures are required to maintain a minimum front street setback of 25 feet, a side yard setback of 10 feet (which may be reduced to 8 feet for one side), and a rear yard setback of 25 feet for interior lots. Additionally, the aggregate width of both side yards in the R-20 One-family Dwelling district must equal at least 30 percent of the total lot width.

Primary Structure Setback Requirements

The R-20 One-family Dwelling district in Arlington County follows specific placement regulations for principal buildings. These requirements ensure adequate open space and maintain the low-density character of the neighborhood [Section 3.2.1].

Setback Type	Minimum Requirement for R-20 District
Front (Street)	25 feet from the street right-of-way line [Section 3.2.6.A.1(e)]
Side Yard (Standard)	10 feet [Section 3.2.6.A.2(b)]
Side Yard (Minimum)	8 feet (permitted for one side only) [Section 3.2.6.A.2(b)]
Aggregate Side Yard	30% of the required lot width [Section 3.2.6.A.2(b)]
Rear Yard	25 feet (required for interior lots) [Section 3.2.6.A.2(b)]

Front Setback Exceptions and Conditions

In the R-20 One-family Dwelling district, the standard 25-foot front setback from the street right-of-way may be adjusted based on the following Arlington County regulations:

Average Alignment: The front setback may be reduced to the average of the distances between the street right-of-way line and the front walls of existing structures on the same frontage [Section 3.2.6.A.1(e)(1)].
Absolute Minimum: Under no circumstances can the front wall be closer than 15 feet to the street right-of-way line, or 18 feet for a parking garage [Section 3.2.6.A.1(e)(2)].
Centerline Rule: No structure in Arlington County may be located closer to the centerline of any street than 50 percent of the building's height [Section 3.2.6.A.1].
Height Limit near Street: Any structure located within 25 feet of a street right-of-way line cannot exceed 2.5 stories in height [Section 3.2.6.A.1(e)(3)].

Side Yard Aggregate Calculation

Arlington County requires a calculation for the combined width of side yards in the R-20 One-family Dwelling district. Because the R-20 district requires a minimum lot width of 100 feet [Section 5.2.3.A], the aggregate width of both side yards must be at least 30 feet (30% of 100 feet). While one side may be reduced to 8 feet, the other side would then be required to be at least 22 feet to satisfy the aggregate requirement [Section 3.2.6.A.2(b)].

Accessory Building Setbacks

Accessory buildings in the R-20 One-family Dwelling district of Arlington County are subject to different placement rules depending on their size and location:

Distance from Main Building: No addition to a main building shall be located closer than eight feet to any wall of an existing accessory building [Section 3.2.6.A.2(c)(1)].
Large Accessory Buildings: Structures that are two or more stories or taller than 25 feet must be set back at least 10 feet from any lot line and 15 feet from any wall of a main building [Section 3.2.6.A.2(c)(2)].
Eave Placement (Interior Lots): The nearest edge of an eave of an accessory building must be at least one foot from a side or rear lot line [Section 3.2.6.A.2(c)(2)(ii)].
Eave Placement (Corner Lots): The nearest edge of an eave must be at least one foot from a side lot line and 10 feet from a rear lot line [Section 3.2.6.A.2(c)(2)(iii)].

Permitted Encroachments into Setbacks

Arlington County allows certain architectural features to extend into the required setbacks of the R-20 One-family Dwelling district:

Windows and Chimneys: Bay windows, oriel windows (without floor space), and chimneys may encroach up to 18 inches into required yards [Section 3.2.6.A.3(a)(1)].
Architectural Projections: Balconies, eaves, trim, fascia boards, and stoops may encroach up to four feet, provided they remain at least five feet from any property line [Section 3.2.6.A.3(a)(3)].
Porches: On interior lots, porches may encroach four feet into required front and rear yards, provided they are no closer than 21 feet to any street right-of-way line [Section 3.2.6.A.3(a)(4)].
Air Conditioning Units: Mechanical equipment is permitted in required side and rear yards but must be at least eight feet from a side lot line and 10 feet from a rear lot line [Section 3.2.6.A.3(b)].

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