Adding electrical outlets in your home is usually a fairly straightforward project, and determining the proper height at which to mount those new outlets just requires a little knowledge and a little common sense. Always follow the National Electrical Code and, of course, your local building codes. Some local codes have additional restrictions and requirements for the placement and wiring of receptacles, switches and fixtures. Always check with your local building enforcement department before adding to or modifying your home's electrical system.
The National Electric Code specifies that there must be a receptacle for every 6 feet of wall space in new construction. The NEC does not specify how high to put them, but there are a few guidelines that will help you determine what height to mount the receptacles you are adding.
Contact your local building code enforcement agency. Be specific about what you intend to do. If possible, speak directly with a building inspector. Tell him which room you are adding the receptacle in and what the intended purpose of the receptacle is. An inspector will be able to tell you whether there is a local height requirement.
Measure the height of other receptacles in your home. Remove the cover plate and measure up from the floor surface to the bottom of the receptacle box. Adding a new receptacle at the same height as the others in your home makes aesthetic sense, too, since you will want them to be consistent in appearance.
Orient the new receptacle in the same direction as the others in your home. Some homes have receptacles mounted vertically -- with one outlet on top of the other -- and others have them placed horizontally, with the outlets side by side. In addition, some electricians position the ground slot up or to the right. Others position it down or to the left. Follow the convention already in place in your home.
Consider the layout of your home's furnishings. In a bedroom, for example, add outlets on either side of the bed, rather than a single outlet in the middle of the wall where it will hard to get to. In the living room, placing an outlet behind the couch makes it hard to reach. Putting an outlet at either end allows you to plug in lamps easily.
Extensive remodeling projects give you the opportunity to place all your receptacles, switches and fixtures according to your needs, as long as NEC rules and local codes are followed. Choose a height and follow the height throughout the house; 10 to 14 inches above the surface of the floor is a good height in most cases.
Keep accessibility in mind. People with disabilities must be able to reach receptacles, too; so outlets should be high enough that a person in a wheelchair doesn't have to lean out of the chair. As a guideline, the Uniform Building Code requires that "accessible" receptacles must be at least 15 inches above the floor and no more than 48 inches above the floor.
Countertops are a special case. If you are adding receptacles as part of a kitchen or bathroom remodeling project, remember to consider the height of the backsplash. Place receptacles high enough that a backsplash won't interfere with the cover plates, but not so high that they bump into upper cabinets.