Secondary Living Unit and Accessory Dwelling Standards in Arlington
In the City of Arlington, the maximum square footage for a detached accessory structure, such as a Secondary Living Unit (ADU), is limited to 50 percent of the floor area of the principal structure. Additionally, the total combined floor area of all structures on the lot must not exceed the maximum lot coverage percentage established for the specific residential zoning district. Secondary Living Units are further restricted to use by family members or relatives and may not be rented or leased to the general public [Section 3.3.5.A.3 and Section 12.3.5.N].
General Floor Area and Size Limitations
The City of Arlington Unified Development Code regulates the size of accessory dwellings primarily through a proportional relationship with the main residence. For any detached accessory structure, which includes detached secondary living units and garage apartments, the floor area cannot exceed 50 percent of the floor area of the principal structure [Section 3.3.5.A.3].
While the City of Arlington provides minimum gross living area requirements for primary residences in various districts (such as 2,500 square feet in the Residential Estate district), Secondary Living Units are expressly exempt from these minimum size standards [Section 3.2.1.B.1 and Section 3.3.6.L.1].
Maximum Lot Coverage Constraints
Every Secondary Living Unit must also comply with the maximum lot coverage standards of its underlying zoning district. Lot coverage is defined by the City of Arlington as the percentage of a lot covered by primary and accessory buildings [Section 4.1.4.A]. The following table outlines the maximum allowable coverage for residential districts where these units are typically permitted:
| Zoning District Name | Abbreviation | Max Lot Coverage (%) |
|---|---|---|
| Residential Estate | RE | 40% |
| Residential Single-Family 20 | RS-20 | 40% |
| Residential Single-Family 15 | RS-15 | 40% |
| Residential Single-Family 7.2 | RS-7.2 | 40% |
| Residential Single-Family 5 | RS-5 | 40% |
| Residential Medium-Density 12 (Single-Family) | RM-12 | 60% |
| Village on the Green at Tierra Verde | VG | 40% |
| Small-Lot Development (Unplatted Tracts) | N/A | 70% |
[Section 2.2.2 through Section 2.2.7 and Section 5.5.6.D.1]
Specific Development Standards by Unit Type
The City of Arlington distinguishes between several types of accessory dwellings, each with specific functional or occupancy limitations that may impact the viable design and size of the unit.
Secondary Living Units
A Secondary Living Unit is a second single-family residential unit located on the same lot as the primary home. In the City of Arlington, these units must provide independent provisions for living, sleeping, cooking, and sanitation. They are permitted to be either attached or detached. If attached, the unit must have a separate independent entrance that is not connected to the primary structure [Section 12.3.5.N].
Caretaker’s Quarters
When established as an accessory use in the City of Arlington, Caretaker's Quarters are subject to strict internal limits. These units are prohibited from containing more than one bedroom, one kitchen, or one bathroom [Section 3.3.6.C.1.b].
Garage Apartments
In specific higher-density districts such as Residential Medium-Density 12 (RM-12) or Residential Multi-Family 22 (RMF-22), a garage apartment is permitted but must be counted as a full dwelling unit for the purposes of calculating the allowed density on the site [Section 3.3.6.F].
Height and Setback Requirements
Regardless of the floor area, all accessory structures in the City of Arlington are limited to a maximum height of 24 feet [Section 3.3.5.D]. They must also adhere to the following setback requirements:
- Front Setback: Prohibited between the front property line and the front facade of the main building [Section 3.3.6.A.3.a].
- Side and Rear Setbacks: Generally required to be at least five feet from the property lines [Section 3.3.6.A.3.b].
Sections Cited
- Section 2.2.2, Residential Estate | RE
- Section 2.2.3, Residential Single-Family-20 | RS-20
- Section 2.2.4, Residential Single-Family-15 | RS-15
- Section 2.2.5, Residential Single-Family-7.2 | RS-7.2
- Section 2.2.6, Residential Single-Family-5 | RS-5
- Section 2.2.7, Residential Medium-Density | RM-12
- Section 3.3.5, General Standards for All Accessory Uses and Structures
- Section 3.3.6, Supplemental Accessory Use Standards
- Section 4.1.4, Lot Coverage
- Section 5.5.6, Residential Design Standards for Small Lot Development
- Section 12.3.5, Accessory Uses and Structures