Building Height Measurement and Calculation in Arlington County
Arlington County determines building height based on the vertical distance from the existing or approved grade to a specific point on the roof, which varies by roof style. In Residential (R) districts, calculation is based on the average of four specific perimeter points, whereas other districts utilize a site-wide perimeter average. Specific vertical projections, such as mechanical penthouses and steeples, are generally permitted to exceed standard district height limits by up to 23 feet provided they meet concealment requirements.
General Measurement Methodology
In Arlington County, the specific point on a structure used to measure height depends entirely on the roof configuration [§3.1.6.A]:
- Flat Roofs: Measured to the highest point of the roof surface or coping.
- Mansard Roofs: Measured to the deck line.
- Gable, Hip, or Gambrel Roofs: Measured to the mean height level (the midpoint) between the eaves and the highest ridge point.
- Dormer Exception: If a dormer exceeds 50 percent of the horizontal width of the roof on any side of the building, that dormer roof is considered the main roof for that side, and height is measured to the midpoint between the dormer eaves and its highest ridge point.
Calculation of Grade
Arlington County uses two distinct methods for establishing the base grade from which height is measured, depending on the zoning district [§3.1.6.A.1-2]:
Residential (R) Districts (excluding RA districts)
The "average existing grade" is calculated by averaging the existing grade at four points on the perimeter of the building. These points must include two points on the front and two points on the rear of the structure, specifically at the points closest to the applicable side lot lines.
All Other Districts (including RA districts)
The vertical distance is measured from the calculated average elevation of the existing or officially approved grade at the perimeter of the entire site. However, no wall or structure in any Arlington County district may be exposed more than two stories beyond the number of stories permitted for that specific district.
Permitted Height Exceptions and Projections
Certain architectural and functional features are permitted to exceed the height limits established for a specific Arlington County zoning district, subject to the following standards:
| Projection Type | Maximum Height Above District Limit | Additional Standards |
|---|---|---|
| Mechanical penthouses, steeples, flagpoles, or smokestacks | 23 feet | Must be concealed by exterior architectural material similar to the building walls; cannot provide additional floor space [§3.1.6.B.1]. |
| Noncommercial radio towers or masts | 25 feet | Excludes amateur radio antennas [§3.1.6.B.2]. |
| Chimneys and smokestacks (integral to a mechanical penthouse) | 27 feet | Must be part of the penthouse structure [§3.1.6.B.3]. |
| County government and public school communication facilities | 50 feet | May exceed the height of the existing structure or the district limit [§3.1.6.B.4]. |
| Rooftop amenity spaces | 23 feet | Only where expressly allowed by the district or Article 9; gross floor area counts toward F.A.R. [§3.1.6.B.6]. |
Amateur Radio Antennas: These are limited to a total height of 75 feet above ground level and must be located in side or rear yards. They cannot be placed on mechanical penthouses [§3.1.6.B.5].
Standard Height Limits by District
Standard height limits are established for each Arlington County zoning district. Special exceptions may be granted by the County Board for additional height in exchange for community benefits or affordable housing.
| Zoning District Category | One-Family Dwelling Limit | All Other Uses Limit |
|---|---|---|
| S-3A (Special District) | 35 feet | 45 feet [§4.2.3.A] |
| S-D (Special Development) | 35 feet | 45 feet [§4.3.3.A] |
| P-S (Public Service) | 35 feet | 75 feet [§4.4.3.A] |
| R-20, R-10, R-8, R-6, R-5 | 35 feet | 35 feet [§5.2.3, §5.7.3] |
| RA14-26, RA8-18 | 35 feet | 35 feet [§6.2.3, §6.3.4] |
| C-1, C-1-R (Commercial) | 35 feet | 35 feet [§7.6.3, §7.7.3] |
| C-2 (Service Commercial) | 35 feet | 45 feet [§7.17.4] |
Sections Cited
- §3.1.6. Height
- §4.2.3. Density and dimensional standards (S-3A)
- §4.3.3. Density and dimensional standards (S-D)
- §4.4.3. Density and dimensional standards (P-S)
- §5.2.3. Density and dimensional standards (R-20)
- §5.7.3. Density and dimensional standards (R-5)
- §6.2.3. Density and dimensional standards (RA14-26)
- §6.3.4. Density and dimensional standards (RA8-18)
- §7.6.3. Density and dimensional standards (C-1-R)
- §7.7.3. Density and dimensional standards (C-1)
- §7.17.4. Density and dimensional standards (C-2)
- §18.2. General Terms Defined (Story)