FAQ: Accessory Dwellings
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Accessory dwelling units are secondary dwellings added to the property of a principal dwelling. A dwelling unit must contain cooking, sleeping and bathing facilities. A kitchen must have cooking equipment and a sink, while a bathroom must have a sink, toilet and shower or bathtub. The two types of accessory units that the town has defined are freestanding units (such as garage apartments or "granny flats") and in-home units (units that are fully attached to the main dwelling, such as an efficiency apartment or basement apartment).
Yes. The town amended the Unified Development Ordinance in June 2017 to update rules for accessory units. Accessory units fall into two categories: freestanding units and in-home units. The requirements for the two types of units are similar but not identical.
The following additional requirements apply to both freestanding and internal accessory units:
- The accessory unit does not exceed 50 percent of the heated living area of the principal dwelling or 800 square feet, whichever is less.
- Each building lot is limited to one principal and one accessory dwelling. Therefore, a property owner could not take advantage of both provisions to have internal and freestanding units on one lot, and no lot could have two accessory units of the same type.
- Parcels being considered for accessory units must front a public street and must have municipal water and sewer service.
- The accessory and principal dwellings must comply with relevant setback requirements based on zoning. Therefore, an existing accessory building that was built with a 5-foot setback provision cannot be converted to a dwelling.
- Applicants must provide at least three off-street parking spaces: two for the principal dwelling and one for each bedroom in the accessory unit.
- Applicants must be able to show they can accommodate waste and recycling rollout containers on site in compliance with the town Code of Ordinances. The receptacles cannot be stored at the curb.
Units that existed on Aug. 12, 1996, may continue as legal non-conformities even if they do not meet the current requirements.
The parcel must be zoned Residential 10, Residential 15 or Residential 20 (R-10, R-15 or R-20). These are the designations common to neighborhoods before the town implemented special use zoning around the year 2000. Some newer neighborhoods (including Waterstone Estates, Forest Ridge, Fiori Hill and Collins Ridge) are in special use zoning districts and would not be able to build freestanding units. These neighborhoods are built to higher densities and often don’t have lots large enough to accommodate a freestanding unit.
The accessory unit must have its own exterior access. If interior access to the principal dwelling is provided, it must be lockable from both dwellings.
Tiny houses are part of the small house movement, a return to houses of less than 1,000 square feet. Many of the tiny houses seen on television or through social media and print publications are movable homes built on a trailer or chassis. At this time, such structures do not meet the state building code of one- and two-family dwellings and do not meet the U.S. Department of Housing and Urban Development standards for mobile homes. As such, they cannot be approved as permanent dwellings and are not acceptable accessory dwellings in Hillsborough. If the state code is changed to accommodate this dwelling type, the town will consider including tiny houses as referenced above as acceptable.
Some tiny houses are built to recreational vehicle standards. The town allows recreational vehicles to be parked in residential neighborhoods, and the town also allows them to be occupied on a guest basis for two-week intervals or as temporary dwelling space during construction or renovation of a dwelling on the same parcel. A tiny house built to recreational vehicle standards would be acceptable for these temporary purposes, but not as a permanent dwelling.
A small (or tiny) dwelling built to state building code for one- and two-family dwellings would be acceptable under the accessory dwelling provisions.
Yes. Some neighborhoods may have covenants that restrict multiple units. These covenants are private restrictions that apply throughout a neighborhood and are enforced by a homeowners association. The town cannot enforce these restrictions, so property owners are responsible for checking with their homeowners associations before applying for permits.