How to Wire a house Addition

However big or small your house addition is, there’s a good chance you’ll need to give it with electrical power. When adding a workroom, bathroom or a couple of bedrooms for family expansion, building codes and common sense dictates placement of electrical outlets and lighting. Even something as small as a backyard window may benefit from an additional lighting fixture. Planning ahead and consulting local code requirements before you construct will help save you money and time.

Electrical Supply

A scaled floor-plan is the best place to begin your wiring layout. First, choose whether you will supply power to the addition from the home’s main service panel or if you need to install a sub-panel in the addition. For a big addition where you anticipate the demand for many circuits or high energy use, a sub-panel makes sense, as it lessens the amount of supply wires you have to rush to the addition in addition to providing you a closer location to shut off power for future maintenance or in a crisis. Estimate the amperage required by each standard, 110-volt household circuit in addition to any high-demand 220-volt circuits necessary for heating, cooking or cooling. Gauge the entire amperage requirement when buying a sub-panel.


Circuit breaker capacity have to match the safe carrying limits of their wiring. Most conventional lighting circuits can be safely run on a 15-amp breaker utilizing 14/2 wire. Common wiring for 110-volt household circuits is designated by the wire gauge and the amount of conductors. The term 14/2 describes 14-gauge wire with 2, typically one black and one white, conductors. While conventional household wiring really has three conductors, the bare ground wire is not included in the count. For circuits intended for heavier demand functions like appliances or computers, use heavier 12/2 wiring with a 20-amp breaker.


Most of the time, the very best time to install wiring in the addition is after the outer sheathing is installed and before drywall is applied to the interior. At this point in construction, the inside of the addition is guarded from the weather and also the wall studs remain easily accessible. Plumbing also needs to be installed before wiring. Wire is more elastic than copper or PVC pipe and also easier to re-route if necessary.

Licenses and Inspection

Consult your local code enforcement agency before you install any wiring. Exact conditions for socket spacing, ground and circuit demands differ somewhat from 1 place to another. In most cases, a building permit and reporting are required before a certificate of occupancy is issued. The very best time to call for an electrical inspection is after the wiring is complete and before the walls have been enclosed with drywall or paneling. This is particularly important when you are doing the job yourself and have very little experience with power. The inspector will point out any safety concerns and explain to you how you can correct them prior to approving the work.

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