Detached ADUs and guest houses on the North Carolina coast

Will it have a kitchen? How many bedrooms? One story or two? Each answer brings rules of its own, so we look them up for your lot first.

What you decide

• A kitchen, or none
• How many bedrooms
• Where it sits on the lot
• One story or two
• How water, power and drains reach it

Each choice sets off rules of its own. A kitchen makes the building a dwelling under the code. Each bedroom counts on a septic system. Where it sits brings in the setbacks, and a second story has to fit the town's height limit.

The kitchen decides what it is.

Under the state's residential code, a dwelling unit has its own place to live, sleep, eat, cook and wash. Most town codes that define an ADU use the same test, so the cooking is what counts. With a kitchen, your town's ADU rule applies to the building.

A guest house with no kitchen

We also build guest houses, studios and pool houses with no kitchen. With no bedroom, the code calls one an accessory building, and the town's limits for accessory buildings apply. A bedroom changes that, since the code's accessory building holds no sleeping room. Your local building inspector decides how the code reads a guest house with a bedroom.

We build a guest house with a bedroom to the same standard as a house. Some towns set a limit of their own: Wrightsville Beach allows no living space in any accessory building.

Where it sits on the lot

How much room is behind your house? Most towns place a detached unit behind the house or beside it, clear of the lot lines. Leland wants it fully behind the house, and Wilmington keeps it from standing in front. New Hanover County keeps it at least 10 feet from any other structure, and Pender County allows the side yard too.

How the work runs

Design and permits come first, through our six steps. Then the building goes up in this order.

When another kind fits better

A detached garage or workshop with no one living in it is a renovation addition.

No room to build in the yard? Where your town and your lot allow it, a garage conversion turns the garage you have into the unit. Where a town names only a unit over a garage, a garage apartment is the path. Where it allows a unit only inside the house, an in-law suite fits.

How the rules group

Two county rules reach the most communities. New Hanover County allows one by right in most residential districts, up to 1,200 square feet, as in Masonboro and Myrtle Grove. Pender County allows one up to 33 percent of the house's heated floor area, around Rocky Point and Hampstead.

Several towns size the unit against the house. Leland, Shallotte, Wilmington, Boiling Spring Lakes and Burgaw each cap it at a share of the main house. In Wilmington, a lot still in a legacy district, such as R-20, follows the rules in force before December 2021. Surf City keeps the unit no taller than the house, on mainland lots only.

St. James and Southport hold a hearing first. St. James needs a special use permit from its Town Council, for a unit of two bedrooms at most. Southport needs one from its Board of Adjustment. Both cap the unit at 800 square feet. Burgaw holds a hearing in four of its districts.

Some places point to another kind. Carolina Beach recognizes an accessory apartment only inside an existing structure, the kind our in-law suite page covers. In Calabash, the code allows a garage apartment detached from the house on a residential lot, which our garage apartment page covers. Oak Island names a garage apartment too, in one district. Topsail Beach and Sunset Beach name a unit only in business districts. Wrightsville Beach keeps accessory buildings small and low, and Kure Beach holds them to one story.

Where the code names no ADU

Holden Beach, Caswell Beach and Ocean Isle Beach name no ADU of any kind. There a detached unit is a question for the town office, one lot at a time. Holden Beach sends it to Planning and Inspections, and Caswell Beach to its zoning administrator. On Ocean Isle Beach's island, any outbuilding stays inside the house's footprint, and the planning office answers for mainland lots.

Code in force

2018 North Carolina Residential Code. A detached unit with a kitchen is a new dwelling under it (Sections R101.2 and R202).

Near the house

Walls less than 5 feet from a line drawn between the two buildings resist fire for an hour (Table R302.1).

Bedrooms

Each has an emergency escape and rescue opening to the yard (Section R310).

Alarms

Smoke alarms in every bedroom and on each story; carbon monoxide alarms with a fuel-fired appliance or fireplace (Sections R314, R315).

A kitchen makes it a dwelling.

The code defines a dwelling unit as complete, independent living space, with room to live, sleep, eat, cook and wash. A detached unit with a kitchen meets that test. The code's scope takes in one or more detached houses on a parcel, so the unit is built as a house in its own right.

Close to the house, the walls resist fire.

The code measures how far a wall stands from an imaginary line drawn between two buildings on the lot. With two homes on one parcel, a wall less than 5 feet from that line has to resist fire for an hour. Several zoning rules keep the buildings farther apart than that: at least 10 feet in St. James, Surf City and New Hanover County.

A guest house with no kitchen and no bedroom is an accessory building. It needs no fire-rated wall facing the house, and past 12 feet in any dimension it is built to the residential code.

Every bedroom has a way out.

Each bedroom gets an emergency escape and rescue opening: a window or door big enough to climb out of, opening to the yard. The unit gets its own door to the outside, and its rooms for living, sleeping and cooking have ceilings at least 7 feet high. A second story brings a stair built to the code's limits on rise, run, width and headroom.

A small house needs careful heating and cooling.

A detached unit meets the energy rules for new homes. Small buildings bring their own trouble: a lot of wall and roof for the floor they cover, and equipment that is easy to oversize. Our ADU page explains why. Sizing the equipment and airtightness without stuffy interiors cover how we handle it.

Septic counts bedrooms.

State rules size a unit's septic needs by its bedrooms. Each bedroom adds to the daily flow the drain field has to take. For the tank, the unit and the house are sized together, and the unit does not count as a separate dwelling. Adding that flow needs sign-off before work starts, from the county's Environmental Health office or an authorized private evaluator. For a guest house with no kitchen, whoever gives that sign-off decides whether its bedroom adds flow.

Is your lot on septic? Then the septic answer on the new bedrooms shapes the plan as much as the town's size cap does.

Water, sewer and power

New Hanover County asks for the provider's proof of capacity, unless the subdivision's approval already counted the unit. In unincorporated Brunswick County, an accessory building usually takes its water, sewer and other utilities from the house. The Planning Director can allow separate meters. Whether the unit can have an electric meter of its own is a question for the power company and your town or county.

An address of its own, or the house's

The rule depends on where you build. Pender County gives an accessory residence a new address. St. James requires the unit to share the house's mailing address and mailbox. Elsewhere, the local addressing office answers.

Parking and the driveway

Most towns with a parking rule add at least one space for the unit. Boiling Spring Lakes asks for one per bedroom, and Leland for two once the unit passes 800 square feet. Southport, St. James and New Hanover County, outside its RA district, require the unit to use the house's driveway. In St. James, a lot that also has a rear alley or a second street can use that instead.

Some lots bring tree rules.

In unincorporated New Hanover County, a lot under an acre in a residential district is exempt from the tree rules. Where the rules apply, removing a regulated tree takes a permit, issued before any clearing or building permit.

Your community may review it too.

A covenant or an owners' association has its own say, apart from the town's rule. Inside the gates at St. James, the property owners' association reviews plans before the town's permits. In Leland's gated and master-planned communities, and inside the gates at Porters Neck, a covenant can add terms of its own.

A historic district reviews the outside.

Inside a local historic district, a new building's exterior needs a certificate of appropriateness before it goes up. In Southport, the certificate comes before the building permit. In Wilmington's HD, HDR and HDMU districts, that same review sets the unit's setbacks.