Adding a room, a second story, or an in-law suite to your Aiken home is a major investment, and the electrical work is one of the most critical components to get right. Unlike a simple renovation where you might update fixtures or add a few outlets, a home addition creates entirely new living space that needs its own circuits, lighting, and often its own subpanel. Planning the electrical system early in the design process prevents costly changes during construction and ensures your addition meets current building codes.
Step One: Evaluate Your Existing Electrical Panel
Before designing the electrical layout for your addition, you need to know whether your current panel can handle the additional load. This is the single most important assessment in the entire project.
A licensed electrician performs a load calculation based on NEC Article 220, which accounts for your existing home's electrical demands plus the new addition's projected needs. The calculation considers square footage, appliance loads, HVAC equipment, and any special circuits.
Common scenarios we encounter in Aiken:
- 100-amp panel: Almost certainly needs upgrading. A 100-amp service barely handles a modern home without an addition. Adding rooms, HVAC, and circuits will exceed capacity. Plan for a 200-amp upgrade as part of the project.
- 150-amp panel: May work for a small addition like a single bedroom or sunroom. A load calculation is essential to confirm. If the addition includes HVAC or a kitchen, you will likely need a 200-amp upgrade.
- 200-amp panel: Usually sufficient for most additions, depending on existing load and available breaker spaces. If the panel is already nearly full, a subpanel in the addition is the typical solution.
Discovering a panel upgrade is needed mid-construction causes delays and budget overruns. Get the load calculation done during the planning phase so the panel upgrade can be included in the project scope and budget from the start.
When You Need a Subpanel
A subpanel is a smaller electrical panel installed in or near the addition, fed by a dedicated circuit from the main panel. Subpanels are the standard approach for additions that need multiple circuits, and they offer several advantages.
Benefits of a subpanel for additions:
- Shorter wire runs from the subpanel to outlets and fixtures in the addition, reducing material costs and voltage drop
- Easier troubleshooting since all addition circuits are grouped together
- Dedicated breaker space without overcrowding the main panel
- Ability to shut off power to the addition independently for maintenance
A typical subpanel for a home addition is 60 to 100 amps with 12 to 24 circuit spaces. The size depends on what the addition includes. A bedroom and bathroom addition might need 60 amps, while a full in-law suite with a kitchen, laundry, and HVAC needs 100 amps or more.
The subpanel connects to the main panel through a feeder circuit sized to match the subpanel's capacity. For a 100-amp subpanel, this is typically #3 AWG copper or #1 AWG aluminum wire in conduit, run from the main panel to the subpanel location. The distance between the panels determines wire gauge, as longer runs require larger wire to compensate for voltage drop.
Matching Existing Wiring
One of the trickiest aspects of addition electrical work is connecting new wiring to an existing home. The new work must meet current NEC standards, but it also needs to integrate cleanly with the existing electrical system.
Common matching challenges:
- Wire type: Older Aiken homes may have NM-B cable (Romex), armored cable (BX), or even knob-and-tube wiring. New work must use current-standard NM-B cable or MC cable depending on the application. Where new wiring connects to old, proper junction boxes and connections are required.
- Grounding: Many older homes have two-wire circuits without a ground conductor. The addition must have proper grounding throughout. Where new grounded circuits connect to ungrounded existing circuits, the electrician must establish grounding back to the panel.
- AFCI and GFCI requirements: Current code requires arc-fault circuit interrupter (AFCI) protection for bedrooms, living rooms, and most habitable rooms. GFCI protection is required for bathrooms, kitchens, laundry areas, garages, and outdoor outlets. Your addition must meet these current requirements even if the existing home does not.
An important point: the existing home's electrical system does not need to be brought up to current code just because you are building an addition. Only the new work and any existing circuits you modify must comply with current standards. However, if the inspector identifies safety hazards in the existing system during the inspection, they may require corrections.
Permits and Inspections in Aiken County
All home additions in Aiken County require building permits, and the electrical work is inspected separately from the structural and mechanical work. Here is what to expect.
Permit requirements:
- An electrical permit is required for all new circuits, panel work, and wiring in the addition
- The permit application must include an electrical plan showing outlet locations, circuit assignments, panel schedules, and load calculations
- Only licensed electrical contractors can pull electrical permits in Aiken County (homeowners cannot self-permit electrical work on additions)
- Permit fees are typically based on the scope of work and are separate from the building permit
Inspection stages:
- Rough-in inspection: Called after all wiring is run through open walls and ceilings but before insulation and drywall. The inspector checks wire routing, box fill calculations, proper stapling and support, circuit identification, and grounding connections
- Final inspection: Called after all devices, fixtures, and cover plates are installed. The inspector tests GFCI and AFCI devices, verifies outlet polarity and grounding, checks fixture installations, and confirms the panel schedule is complete and accurate
Scheduling inspections promptly keeps your project on track. A failed rough-in inspection means the drywall crew waits until corrections are made and the inspection passes. This is why hiring a qualified electrician who understands current code is so important for addition projects.
Code Requirements Specific to Additions
Beyond the standard NEC requirements for outlets, circuits, and protection devices, additions trigger several specific code considerations:
- Smoke and carbon monoxide detectors: New additions must have interconnected smoke detectors in every bedroom, outside sleeping areas, and on every level. If the addition includes a fuel-burning appliance or attached garage, carbon monoxide detectors are also required. These must be hardwired with battery backup and interconnected with the existing home's detectors.
- Exterior lighting: The NEC and local codes require lighting at all exterior doors of the addition. These must be controlled by a wall switch inside the addition.
- Bathroom requirements: Each bathroom in the addition needs at least one 20-amp GFCI-protected circuit, a ventilation fan (required by IRC for bathrooms without operable windows, and recommended for all bathrooms), and proper lighting at the vanity area.
- Tamper-resistant receptacles: All 15A and 20A outlets in the addition must be tamper-resistant (TR rated). This has been an NEC requirement since 2008 and applies to all new construction and additions.
- Energy code compliance: South Carolina's energy code may require specific lighting controls, such as vacancy sensors in certain rooms and high-efficacy lighting throughout the addition.
Budgeting for Addition Electrical Work
Electrical work typically represents 10% to 15% of the total cost of a home addition. For Aiken-area projects, here are general ranges:
- Single room addition (bedroom or sunroom): $2,500 to $5,000 for electrical, including circuits, outlets, lighting, and smoke detectors
- Bedroom and bathroom addition: $4,000 to $8,000, including GFCI circuits, exhaust fan, vanity lighting, and heated floor circuit if desired
- In-law suite (bedroom, bathroom, kitchenette, living area): $8,000 to $15,000, including subpanel, dedicated appliance circuits, and full lighting package
- Second story addition: $10,000 to $20,000+, depending on scope. Running new circuits vertically through an existing home adds complexity
These ranges do not include a panel upgrade if one is needed. Add $2,500 to $4,500 for a 200-amp panel upgrade.
Start Planning Early
The earlier you involve an electrician in your addition project, the smoother the process will be. Ideally, your electrician reviews the architectural plans before they are finalized so outlet placement, circuit routing, and panel requirements can be designed into the project rather than patched in later.
Unity Power & Light works closely with general contractors and homeowners on addition projects throughout the Aiken area. We handle everything from the initial load calculation through final inspection, ensuring your addition's electrical system is safe, code-compliant, and built to serve you for decades. Contact us for a free consultation on your upcoming project.