Accessory Buildings are separate structures on a lot that are subservient, or incidental, to a primary dwelling in either form or function. An accessory building must have a separate means of egress. An accessory building is a building that is roofed over and more than 50% of its exterior walls are enclosed.

This is a broad umbrella term that encompasses a wide variety of structures including barns, stables, man-caves, she-sheds, (partially enclosed) carports, tree houses, garage units, garage apartments, pool-side bath houses, guest houses, woodworking shops, and tool sheds.

An ADU is a separate structure on a lot that has been equipped for housing. All ADUs are accessory buildings, but not all accessory buildings are ADUs.

Other names include, but are not limited to, granny flat, in-law-suite, garage apartment, laneway house, alley house, backyard cottage.

The primary feature that distinguishes an accessory dwelling unit from other accessory buildings is the presence of conditioned living areas and built-in or semi-permanent cooking facilities (like a conventional stove appliance, but not necessarily a counter top cooking appliance).

The UDO regulates design principles for ADUs in Section 5.4.1. Some Design and Design/Build firms in Durham are familiar with ADUs, some even specialize in it.

In North Carolina a General Contractor is required on all jobs over $30,000, with an exemption for your personal property. Thus, so long as you live in the primary dwelling, you can GC your own ADU project, subject to some restrictions. There are many reasons to do this and to not do this.

The maximum size of an ADU in Durham is capped at 800 square feet.
The maximum height of an ADU in residential areas is 25 feet.

Setbacks are dimensional limitations placed on a property, based on zoning district, which restrict the location of various development elements such as a single-family home, or accessory dwelling unit. Typically, setbacks are from property lines, but can also be associated with things such as easements or structures.

Setbacks for ADUs are determined by the same requirements for accessory structures, see UDO Section 5.4.1.

There may be further restrictions on location depending on zoning and type of primary structure. See UDO Section 5.4.2 and UDO Section 7.1 for setback requirements based on housing type and zoning district.

An ADU is also permitted to be attached or within the primary home or duplex.

Setbacks are measured to the foundation of the structure. Other building elements have different setbacks, see UDO Section 6.12.3.

You can consult the Durham planning department, the GIS, and the UDO section 5.4.1 for information on your zoning and the restrictions in place for that district.

The UDO lays out these principles for ADUs:

• An accessory structure shall be clearly subordinate to the primary structure in aspects of size and purpose.

• The maximum height of an accessory structure in residential areas shall be 25 feet.

• Accessory dwellings that are an addition to the primary structure shall conform to the applicable height limits for the primary structure.

• The structure shall be compatible with the primary structure in style, materials, roof form, and details.

Other design principles to consider:

• Match roof pitch, Avoid oversized dormers

• Consider flexibility - the space may be used for guests, grad students, families, short term or long term, those seeking medical treatment, those giving medical treatment, students, seniors, mothers in laws, fathers in laws, etc.

A firewall is a partition or horizontal assembly (floor system) designed to inhibit or prevent the spread of fire. They are sometimes required between different building occupancies. For example, there are typically firewalls between two stores in the same building.

Accessory dwelling units (ADU) are regulated through the Residential Building Code. This code requires firewalls between an attached accessory dwelling unit and the main house. See Section R302.3.

R302.3 Two-family dwellings. Dwelling units in two-family dwellings shall be separated from each other by wall and/or floor assemblies having not less than a 1-hour fire-resistance rating when tested in accordance with ASTM E119 or UL 263. Fire-resistance-rated floor-ceiling and wall assemblies shall extend to and be tight against the exterior wall, and wall assemblies shall extend from the foundation to the underside of the roof sheathing.

Exceptions:

1. A fire-resistance rating of 1/2 hour shall be permitted in buildings equipped throughout with an automatic sprinkler system installed in accordance with NFPA 13.

2. Wall assemblies need not extend through attic spaces when the ceiling is protected by not less than 5/8-inch (15.9 mm) Type X gypsum board and an attic draft stop constructed as specified in Section R302.12.1 is provided above and along the wall assembly separating the dwellings. The structural framing supporting the ceiling shall also be protected by not less than 1/2-inch (12.7 mm) gypsum board or equivalent. R302.3.1 Supporting construction. When floor assemblies are required to be fire-resistance rated by Section R302.3, the supporting construction of such assemblies shall have an equal or greater fire-resistance rating.

This code section describes both firewall partitions (vertical) and floor systems (horizontal assemblies). The short summary is that 1 hour firewalls are required (without a sprinkler system) between the main house and accessory dwelling units. This is fairly straightforward is the ADU is attached laterally to the main house. The requirements get a little bit more complex if you stack units (all or part of an ADU over or under the main residence). This configuration requires that the walls that support the horizontal fire assemblies to also be firewalls.

While the jump from single family detached to duplex triggers additional code requirements in the International Residential Code (IRC), if an ADU is attached to a duplex, it will likely be reviewed as a triplex and thus push the project into the cost-prohibitive International Building Code? Put another way the IRC covers 1-2 family structures. Any structure with 3 or more units will be in the IBC. The IBC requires larger stairwells, sprinklers, accessibility, etc. Needless to say, if affordability is the goal, the IRC is much simpler and less restrictive. The IBC adds additional processes and requirements, with added costs. Any sincere quest for affordability should seek to stay in the residential code.

In general, setbacks are eliminated except where adjacent to a non-DD residential District or use. Side setbacks are 0’.Rear setbacks vary. From UDO 16.2.1.C, no rear yard is required in the DD-C or DD-S1, subdistricts. In DD-S2 subdistrict no rear yard is required unless adjacent to a non-DD residential district or use, in which case a 25’ rear yard is required. In the CD and CSD subdistricts a 10’ minimum rear yard is required.

In Durham ADUs do not require any additional off street parking spaces. (UDO 5.4.2.B.1.b.4)

Currently, financing options for ADU’s are limited.

Homeowners typically either self-finance (cash, savings, friends/family) or receive finances based on the equity in their home. There are three primary loan programs related to home equity.

1. Home Equity Line of Credit (HELOC).

2. Home Equity Installment Loan (HEIL)

3. Cash Out Refinancing

Each option has a variety of benefits and drawbacks, and homeowners should discuss the details of their situation with a financial institution.

If a homeowner does not have the ability to self-finance nor has the equity in their home necessary to build an ADU, their options are limited as lenders are not broadly experienced or interested in underwriting ADU’s.

The City of Durham is working to establish a lending source for low-income homeowners for the development of ADUs. This is yet to be established.

Self-Help Credit Union (HQ in Durham) has a pilot ADU loan program in Los Angeles. If successful, they may bring the program to Durham in the future, but this is not currently an option.

Additionally, a developer or builder of ADUs may consider custom financing options with specific homeowners.

In Durham no special use permit is required (UDO 5.4.B.1.b.5). However, all improvements to real property require a building permit. This is done administratively at the Development Review Office in the basement of City Hall.

For permits, you will need construction drawings including: floor plans, elevations, structural calculations and (if there is new footprint) a site plan.

Though not required, typically plans will also include electrical, and can include as much detail as desired on architectural trim, finishes, fixtures, etc. Plans are usually done by an architect or designer. Structural work, mostly sizing of footings and framing lumber, is generally done by a structural engineer. On smaller projects, they are sometimes specified by a general contractor or architect.

You can do custom drawings on work from one of the many stock plans drawn by the Durham Architect’s Guild. Plan reviews typically take 1-2 weeks, after which you can pick up the approved drawings and break ground.

Impact fees are typically broken into four levies: Sewer, Tap, Capital Facility Fee., $5500 per.

As of February 2020, Accessory Building Permits cost $100 ($50 if there is no footing), + $50 Plan Review Fee, and Impact Fees.

Per the latest City Impact Fee Ordinance:

• Street Impact Fees of $293, $531 or $1,405 depending on which Economic Impact Zone the site is located in.

• Open Space Fees of $222

• Parks and Rec Facility Impact Fees of $425

Both NC Residential Building Code and the state administrative code control sewer connections for ADUs. Building Code requirements for ADUs are basic and identical to sewer requirements for all other single family dwellings. Since 2017, Durham Public Works has intermittently enforced an arcane part of the state administrative code that had previously been ignored. Functionally, this interpretation forced builders of detached ADUs to install a new sewer tap at great (and unnecessary) expense to the owner. 15A NCAC 02T prohibits connecting two separate buildings on the same parcel to the same sewer tap without a special permit issued by NC Department of Environmental Quality. In February 2020, NCDEQ implemented a system meant to issue permits for a shared sewer line serving an ADU or an accessory structure or accessory building under narrow circumstances and subject to recording a deed restriction on the property. As of April 2020, DEQ had received approximately 10 applications for Certificates of Compliance; no certificates had been issued.

Water may be combined. This would require an owner to pay for, or separately rebill, water or electric, which from a sustainability perspective is not ideal. Studies show people who are aware of their resource usage tend to use less of that resource. Still, sometimes the meter fees may be cost prohibitive, or there may be co-living situations where shared metering makes more sense, or routing a new water service from meter to ADU may cause more site problems than connecting to existing adequate water piping in the primary dwelling. NC Electrical Code does not require separate electric metering of ADUs in every case. Site constraints could favor serving a detached ADU from the primary dwelling’s electric service or from a separate electric service. In most cases, NC Residential Building code requires that attached ADUs be served from the primary dwelling’s electric service.