Accessory dwelling units are gaining popularity across Aiken County, whether as garage apartments, in-law suites, backyard cottages, or converted spaces above detached garages. These small, self-contained living spaces provide housing flexibility for aging parents, adult children, rental income, or guest accommodations. But every ADU needs a properly designed and permitted electrical system, and that is where planning ahead saves money and headaches.
What Counts as an ADU?
An accessory dwelling unit is a secondary living space on a property that already has a primary residence. In Aiken County, ADUs can take several forms:
- Garage apartments: Living space built above or beside an existing detached garage
- In-law suites: Separate living quarters attached to or within the main house, with their own entrance, kitchen, and bathroom
- Backyard cottages: Freestanding small homes built in the backyard of an existing property
- Converted spaces: Existing structures like workshops, pool houses, or bonus rooms converted into habitable living spaces
- Basement apartments: Below-grade spaces converted into separate living units
Regardless of the type, any ADU intended for habitation must meet the National Electrical Code requirements for a dwelling unit, which are more extensive than the requirements for a workshop or storage building.
Panel and Service Sizing for ADUs
The first major electrical decision for any ADU project is how the unit will receive its power. There are two basic approaches, and the right one depends on the ADU's size, intended use, and your existing electrical service.
Sub-Panel from the Main House
The most common approach for ADUs in Aiken is feeding power from the main house's electrical panel via a sub-panel in the ADU. This works well when the main house has sufficient capacity and the ADU's electrical load is moderate.
A typical ADU sub-panel setup requires:
- Sub-panel size: A 60-amp or 100-amp sub-panel in the ADU, depending on the load calculation
- Feeder cable: Properly sized conductors run from the main panel to the sub-panel, either through conduit underground or through the building if the ADU is attached
- Main house capacity: The main house's panel must have enough spare capacity to support the ADU's load. If the main house has a 200-amp panel that is already heavily loaded, you may need to upgrade the main panel before adding the ADU feeder.
- Grounding: The sub-panel in the ADU must be grounded at the sub-panel location if it is a detached structure, with a separate grounding electrode
The advantage of a sub-panel approach is lower cost. You avoid the expense of a separate meter and utility service. The disadvantage is that the ADU's electrical use shows up on the main house's utility bill, which complicates things if you plan to rent the ADU.
Separate Service with Its Own Meter
For ADUs that will be rented or that need complete electrical independence, a separate electrical service with its own meter is the better choice. This means the ADU has its own utility account, its own meter base, and its own main panel.
A separate service requires:
- Utility coordination: Dominion Energy or your local utility must approve and install the new meter. This involves an application, a new service drop or underground service lateral, and a meter base that meets the utility's specifications.
- New meter base: Installed on the ADU or on a meter pole near the structure
- Main panel: A 100-amp or 200-amp main panel in the ADU, sized based on the load calculation
- Separate billing: The ADU occupant receives their own utility bill
The cost of a separate service is higher because of the meter base, utility connection fees, and additional infrastructure. But for rental units, it simplifies billing and makes the arrangement cleaner for both landlord and tenant.
NEC Requirements for ADU Electrical Systems
The National Electrical Code treats ADUs as dwelling units, which means they must meet all the same electrical requirements as a house. Here are the key requirements:
Kitchen Circuits
If the ADU has a kitchen, it needs a minimum of two 20-amp small appliance circuits serving the countertop outlets, plus a dedicated 20-amp circuit for the dishwasher if one is installed. The refrigerator should also be on its own dedicated circuit. Kitchen countertop outlets must be GFCI-protected and spaced so that no point along the counter is more than 24 inches from an outlet.
Bathroom Circuits
Each bathroom needs at least one 20-amp circuit dedicated to bathroom outlets. All bathroom outlets must be GFCI-protected. The bathroom circuit can serve multiple bathrooms but cannot serve outlets outside of bathrooms.
Bedroom AFCI Protection
All circuits serving bedrooms in the ADU require arc-fault circuit interrupter (AFCI) protection. This includes outlet circuits, lighting circuits, and any other circuits in bedroom spaces. AFCI breakers detect arcing faults that can cause fires and are required by current code for all dwelling unit bedrooms.
Smoke and Carbon Monoxide Detectors
ADUs must have interconnected, hardwired smoke detectors in each bedroom, outside each sleeping area, and on each level of the unit. If the ADU has any fuel-burning appliances, a gas furnace, or an attached garage, carbon monoxide detectors are also required.
Outdoor and Garage Receptacles
At least one outdoor GFCI-protected outlet is required at the front and back of the ADU (if it has both). If the ADU includes a garage space, the garage needs at least one GFCI-protected outlet.
HVAC Circuits
The ADU's heating and cooling system needs its own dedicated circuit. Mini-split systems, which are popular for ADUs because of their efficiency and small footprint, typically require a dedicated 240-volt, 20-amp or 30-amp circuit. We size the circuit based on the specific equipment being installed.
Permit Requirements in Aiken County
ADU construction in Aiken County requires both building and electrical permits. The electrical permit covers all wiring, panel installation, and connections. Here is what the permitting process looks like:
- Permit application: We submit the electrical permit application to Aiken County Building Department with a description of the work and a load calculation
- Rough-in inspection: After the wiring is installed but before walls are closed up, the county inspector reviews the rough wiring for code compliance
- Final inspection: After all devices, fixtures, and panels are installed and the work is complete, a final inspection verifies everything meets code
- Utility connection: If a separate service is being installed, the utility will not connect power until the final inspection passes
We handle the entire permit process for every ADU project, from application to final inspection. You do not need to visit the building department or coordinate with inspectors yourself.
Common ADU Types and Their Electrical Needs
Garage Apartment
A living space above a detached garage typically needs a 60-amp to 100-amp sub-panel or service, depending on whether it has electric heat, a full kitchen, and an electric water heater. The feeder usually runs underground from the main house or from a new meter on the garage. Considerations include the garage door opener circuit, outdoor lighting, and proper separation between the garage electrical and the living space electrical.
In-Law Suite (Attached)
An attached in-law suite can sometimes be served by the main house's panel if there is sufficient capacity. This is the simplest and most cost-effective setup. The suite still needs its own circuits for the kitchen, bathroom, and bedroom, and all circuits must be properly identified at the panel. If the suite will be a fully independent living space, a sub-panel dedicated to the suite makes management easier.
Backyard Cottage (Detached)
A freestanding backyard cottage requires either an underground feeder from the main house or a separate utility service. The underground run must be properly sized for the distance and load, installed in approved conduit at the correct burial depth, and equipped with a grounding electrode at the cottage. A detached cottage with a full kitchen, electric water heater, and mini-split HVAC system typically needs at least 100-amp service.
Planning Ahead Saves Money
The most expensive part of ADU electrical work is running power to the structure. If you are building new or renovating, plan the electrical early in the process. Running conduit before concrete is poured, coordinating with the utility before walls go up, and sizing the main house panel for the additional load before it becomes a bottleneck are all much cheaper when done proactively.
If you are considering an ADU project in Aiken County, call Unity Power & Light at (803) 220-4491 for a consultation. We will assess your existing electrical system, discuss metering options, provide a load calculation for the ADU, and give you a flat-rate quote for the electrical work.