Kitchen Additions (How to Build Additions Guide: Simple Room Additions)

Some additions involve kitchen and bathroom remodeling, such as enlarging a cramped kitchen by expanding into the yard, building an entirely new kitchen, or adding a second or third bathroom to the bedroom wing.

These projects begin with the basics of a simple ground-level addition. They are more complicated, however, because they require plumbing, complex wiring, efficient space planning, and the coordinated installation of appliances and fixtures.

Using the information presented in this section, you can turn a simple addition into an elegant and efficient kitchen or bathroom.

Light and airy two-story addition features a hot tub and dressing room adjoining the master bedroom. Stairs in background lead to upstairs study.

Kitchen Additions

The kitchen is the nerve center of most homes, with many appliances, fixtures, work areas, storage spaces, and traffic corridors concentrated in one room.

This focus of activity, combined with a bewildering choice of available colors, materials, and styles, makes the kitchen the most complex room to plan and construct. Careful preparation is the key to a successful project. It will most likely mean set ting up a temporary kitchen or making alternative arrangements.

Preparing for Construction

A thorough design, with every detail clearly specified, makes construction easier. It is also important to compare plans with actual site conditions before starting construction, to make sure the proposed addition can be built as designed. Some errors and oversights can be corrected as you proceed, but the job will go much more smoothly if you anticipate as many of them as possible ahead of time. (There will be plenty of new problems to solve during construction.) Even if it means an extra week or two of preparation, dealing with the following issues now will help you avoid costly delays or mistakes during construction.

Walls. Verify thickness of existing walls. Do not assume that walls are framed with 2 by 4s or covered with 1/2-inch finish material. Wall framing thickness is critical for concealing drain- and vent pipes, for ordering new windows (you may need jamb extensions for thicker walls), for sup porting new roof loads, and for matching new walls to old if you plan to extend them.

Also determine whether bearing walls you plan to expose are framed properly, with double top plates, studs centered at 16 inches, and large enough headers for window and door spans. It may be difficult to check ahead of time, but be ready for surprises when you do open up walls.

Measuring walls is also important. The standard height is 8 feet, but measure to be sure. Nonstandard wall height may affect cabinet dimensions, soffit dimensions, location of over head light fixtures, size of wall-finishing materials, or framing techniques for the new addition.

Structural systems. Verify the direction of floor and ceiling joists, exact location of girders or foundation supports, and thickness of sub- flooring. Can the addition’s subfloor be built at the same level as the existing kitchen, or are there underlayments between subfloor and finish floor that must be considered? If so, will they need to be removed?

Plumbing and gas lines. Verify the location and position of existing plumbing and gas lines. Check roof or attic to see where sink vent lines up. Check under floor for sink drain and main house drain. Take accurate measurements to determine exact locations; there must be enough clearance to extend horizontal lines up stream with proper slope (¼-inch per foot). Look for places to tap into cleanouts or other fittings.

Locate water heater and all hot water pipes running to kitchen. Are they insulated? Can you shorten runs for quicker hot water at tap?

Check flue and duct locations in existing structure to verify their locations in plans.

Ceiling insulation. Find out whether ceiling insulation will get in the way of demolition, wiring, or other construction activities. Al though there is no point in removing it early, just knowing whether it's loose fill or blankets will help you prepare for removal.

Doorways. Measure doorways to see whether there will be one wide enough for delivering large cabinets, appliances, countertops, fireplace, and so on to finished kitchen. Most fixtures can fit through standard 32- inch doorways, but if you have corner cabinets or other large items, have them delivered before walls are closed in.

Appliances. Choose appliances and verify manufacturers’ installation specifications. You will need to know framing dimensions and rough-in locations for utility lines long before you install appliances.

Also, measure appliances or cabinets you intend to reuse to be sure they will fit in planned locations.

Finally, decide countertop details such as type of material, height of backsplash, and whether sink will re quire a rim or be set below counter- top (as in some tile installations).

Sequence of Construction

The construction sequence will vary with each job, but the first step usually is to apply for the building permit and arrange for financing.

Next order cabinets, windows, and other materials that take more than two weeks for delivery.

Next line up subcontractors, if you are doing the job yourself, and set a preliminary schedule.

Then begin the site preparation and foundation for the addition, following the guidelines for basic additions presented earlier.

In most cases the addition shell can be framed and closed in before you open the wall and disrupt the kitchen itself. However, this process includes a few additional steps that aren't part of a simple room addition.

+ If plumbing, wiring, or any duct work will be run under the floor, install and have it inspected before applying subflooring, unless basement or crawl space is large enough for full inspections to be made standing up.

+ Install plumbing vents, chimneys, flues, or ventilating ducts that penetrate roof before roofing goes on so they can be flashed properly.

+ If necessary, leave part of exterior wall open to remove cabinets and debris from existing kitchen and to bring in bulky items.

When the addition is closed in, the next step is to demolish as much of the present kitchen as necessary. Make arrangements for removing debris ahead of time. Observe safety precautions such as turning off gas and electricity to the areas where you plan to work, and wearing gloves, goggles, a hard hat, and dust mask.

If the project is a complete renovation, gut the room to the wall studs and ceiling framing. Although it's tempting to leave small sections of wall or ceiling material intact, they are seldom worth saving; patching into them is tedious and you will probably need to get behind them for wiring or insulating anyway. It is only worthwhile when you can save a whole wall.

With the shell completed and the present kitchen gutted, proceed as you would with any new construction, following the guidelines in the next section.

Rough Framing for a Kitchen

Stabilizing a free-standing wing wall:

Rough framing techniques for a kitchen are the same as basic carpentry techniques for any other room, but a few framing details occur more often in kitchens than in other rooms.

Blocking. Wall cabinets are easier to hang if you nail blocking (2 by 10 or 2 by 12) between studs where tops of cabinets will align.

Wing walls. Short walls (2 to 3 feet long) are often used to enclose a refrigerator, define an alcove, or terminate a row of cabinets. If they extend from floor to ceiling, they can be framed like any stud wall, with top plates tied into ceiling joists or into blocking between ceiling joists.

But sometimes a wing wall is designed not to reach the ceiling, to create a feeling of more space and admit more natural light into an al cove. Because such a wall has no support along the top and one edge, it must be stabilized by other means. A corner cabinet, shelving, or counter installed against the wing wall and adjacent wall should be enough to brace the wall as long as the unit is well secured.

If the wing wall is freestanding, assemble the framing with screws in stead of nails; or stiffen the wall by using thicker wallboard (3/8- inch rather than ½-inch) or plywood; or anchor the front edge of the wall by using a long 2 by 4 for the last stud, extending it through the floor, and attaching it to a joist or other framing underneath. This is particularly effective for walls that support extensive tile work.

Kneewalls. (Also called pony walls). Open kitchen designs often have low walls that separate the cooking area from dining, laundry, and other areas. Frame them the same way as full-sized walls, with studs at 16 inches on center, double top plates, and a single soleplate. If one end (or both) is freestanding, stabilize it the same way as a wing wall, adding diagonal or plywood bracing if wall has no support at either end.

Cover framing with wallboard or a similar wall finish and cap the top with a wood, tile, or laminate shelf to match other design accents.

Pass-throughs. Frame a pass- through the same as a window, with a double rough sill across the bottom and a header to span the top of the opening. If you are opening up an existing bearing wall, shore up ceiling joists on each side of the pro posed opening before altering any studs. Rather than completely removing studs from the opening, cut them off at the height of the pass-through, allowing for the double rough sill and finish shelf or trim.

Soffits. Soffits fill the space between ceiling and wall cabinets, and consist of a simple ladder frame covered with wallboard. It is customary to build soffits after covering main walls and ceiling with wallboard. To allow for crooked walls or discrepancies in cabinets, the finished soffit is usually 13 inches wide, even though wall cabinets are only 12 inches wide. This creates a thin overhang just above cabinets, so wallboard should be covered with a corner bead along this edge. The overhang can be painted or wallpapered to match the rest of the soffit, or covered with wood trim.

Frame the soffit with 2 by 2s to make it easier to drive nails or screws in both directions. Choose lumber carefully for straightness; warps or bows will show clearly. You can also use 2 by 3s or 2 by 4s, which require toenailing but are more stable.

Build an L-shaped ladder frame on the floor and then secure it in place overhead by nailing or screwing one rail into ceiling joists and the other into wall studs.

Windows. When framing windows over a sink or countertop, first decide the height of the finished sill—that is, whether to make it flush with the countertop or place it above the backsplash. If the finished windowsill will be flush with the countertop, be sure to take into account any finished flooring material, countertop thickness, thickness of finished sill, and extra clearance for shimming when laying out height of rough sill.

Kitchens and breakfast nooks are ideal places for specialty windows such as garden (greenhouse) windows, bay windows, and bow windows. Framing for these windows is the same as for any window. All you need to know are the rough opening dimensions from the manufacturer.

Ladder soffit: 10d nails hold soffit to studs and joists; Corner bead.

Plumbing for a Kitchen

The basic fixtures for most kitchens are a sink, a disposer, and a dish washer, but your kitchen may also have a bar sink, an ice-making refrigerator, or a washing machine. You may also need a gas line for the range or a cooktop and oven.

Drainpipe and Vent Pipes

The first plumbing consideration is the drainpipe. A kitchen sink with dishwasher requires a 2-inch pipe, which your present kitchen may have already. If you are adding a washing machine to the kitchen drain, most codes require a 3-inch branch drain all the way to the main drain.

If you are extending the drain to a new sink location, you must also consider slope. Drainpipes must slope ¼-inch per foot. This means that if the existing drain is strapped close to the bottom of the floor joists, there may not be enough clearance to extend it to the new fixtures unless the new pipe runs parallel to the joists and can be suspended between them. For a 2-inch pipe it may be possible to bore through the joists if they are 2 by 10s or 2 by 1 2s so that the holes are at least 2 inches from the joist edges. Otherwise, it will be necessary to connect the new drainpipe to the main drain farther downstream in order to get the proper flow.

All plumbing fixtures must be vented to the roof. If you are keeping the sink near the old location you can probably use the same vent. Check local code for “trap arm distance”— the maximum allowable distance between sink trap and vent pipe. (Typical distances are 3 to 5 feet for 1½-inch drainpipe and up to 6 feet for 2-inch.)

Drainpipe between joists; Vent pipe below kitchen window; Venting an island sink

Kitchen sinks often have windows over them, making it impossible to run the vent pipe directly up to the roof next to the sink. Codes prohibit changing the vent pipe direction from vertical to horizontal at any point lower than 42 inches above the floor, a distance higher than most windowsills. To solve this problem you can locate vertical vent pipe alongside the window and run a horizontal trap arm from sink to pipe (as long as it does not exceed the maxi mum trap arm distance of 3 to 5 feet). Or you can offset the vent pipe with two 45-degree fittings to clear the window, thus avoiding a 90-degree change in direction below the 42-inch limit.

Related to the problem of venting a kitchen sink with a window over it's the problem of venting an island sink without installing a vent pipe in the middle of the room. Most codes accept a venting arrangement similar to the diagram shown.

Water Supply Pipes

Run water supply pipes after drain- and vent pipes are installed. The dishwasher requires a 3 supply, usually flexible copper tubing, connected to an angle stop under the sink or dishwasher. A refrigerator with icemaker will need its own cold water supply. Check manufacturer’s specifications for size and location of supply line. Typically it's 3/8-inch tubing with a separate angle stop behind or next to the refrigerator.

Rough-in dimensions. Typical kitchen sink rough-in dimensions are 15 inches above floor for drain stub and 19 inches for hot and cold water supply stubs.

A laundry P-trap is usually installed inside the wall behind the washing machine. It must be between 6 and 18 inches above the floor.

Freeze protection. If you live in a cold climate, take the following pre cautions to prevent frozen pipes:

+ Try to run hot and cold water lines within the insulated area.

+ Tuck blanket insulation under drainpipe.

+ Wrap heat tape around and insulate any water supply pipes that will be vulnerable to freezing.

+ If you use plastic pipe, allow slack for expansion (enough for 6 inches of expansion for every 50 feet of pipe).

+ If you install an outside hose bibb, consider a freeze-proof valve or an extra valve inside the house to shut off the hose bib and drain it for the winter.

Gas lines. If you are relocating a gas range or cooktop, you will have to move the gas line. This may re quire a larger pipe if the run is very long. If you are adding a gas range or cooktop, you may have to enlarge the main gas supply pipe for the entire house to accommodate the increased demand. Consult with a qualified plumber about running new gas lines. Besides obtaining a permit you will need to run a pressure test before completing the installation.

Water supply pipes: Alternate: New shutoff valve in nearby cabinet, Alternate: New shut off valve in basement; Shutoff valves: New shutoff valve and compression coupling for copper tubing under nearby sink, or on cold water in basement or crawl space, or on cold water pipe in nearby bath or utility room

Roughing in Ventilating Ducts

Mechanical ventilation—either a range hood or a down-draft system— eliminates cooking odors, excess water vapor, and buildup of harmful contaminants.

The venting system should be rated to move 200 to 400 cubic feet per minute (CFM) of air for most kitchens, and more for large kitchens. Range hoods should be located 30 inches above the cooking surface (some codes allow 21 inches).

Plan duct installation for the shortest possible run with the fewest turns. The maximum length is usually 25 feet, with turns totaling no more than 180 degrees. The duct must terminate outside, not in the attic or crawl space, with an approved roof or wall cap. The termination cap may require a damper or other means of controlling air movement, as well as an insect screen.

Sheet metal duct sections of various lengths are available in a round shape for running in free space (such as attic or crawl space) or in a rectangular shape for installing between studs. The manufacturer of the ventilating unit specifies duct size (typically 7 or 8 inches for round ducts, 3¼- by 10 inches for rectangular). For greater flexibility, use adjustable rather than rigid elbows. Various transition pieces are available for connecting the duct to the fan unit or joining a round duct to a rectangular one. Duct materials are readily available from sheet metal shops or dealers who supply fan units.

Install duct before insulating, extending it far enough into kitchen space so that remaining pieces can be connected to it when cabinets and hood are installed. Secure each joint with a sheet metal screw, drilling pilot holes if needed. Seal joint with metallic or other approved duct tape. If you run a duct between studs and have to cut through the double top plate, reinforce plate with a metal framing strap.

Range venting options: Range hood and fan, Range hood and fan, Range, Rectangular duct inside cabinet, Round duct between joists, Roof cap

Electrical Wiring for a Kitchen

Wiring is an important part of any kitchen project. Rough wiring consists of installing electrical boxes in the open framing and running wire or cable to them from the circuit breaker panel or other source. First you must plan the circuits, based on the wiring diagram, the working drawings, and local codes.

Typical circuit requirements for a kitchen are:

+ A separate circuit for each permanently installed appliance, including electric range (240v), electric cooktop (240v), electric oven (240v), dishwasher, in-counter blender mo tor, trash compactor, and freezer.

+ At least two 20-amp circuits for countertop and other outlets. Outlets in pantry, breakfast nook, or dining room can be included on these circuits. Codes don't specify how many receptacles can be used on each circuit, but common practice for kitchens is to use no more than six.

Receptacles set over countertops should be located no more than 4 feet apart, with at least one outlet placed over any section of counter that's longer than 12 inches. The height is customarily 42 inches above the finish floor.

+ Lights can't be connected to any of the above circuits. Although it may be possible to wire new lights into an existing lighting circuit, there are usually enough lights in a kitchen to warrant a separate 15-amp circuit for them, especially when a breakfast nook or dining area is included.

Adding new circuits. As you plan new circuits you must consider whether your present electrical system can meet the new demand. There are two things to consider: first, available space for new circuit breakers (including a double space for each 240-volt breaker); and second, the electrical capacity of the main service entrance. If your present panel has few or no empty spaces for new breakers you can either use half- size “wafer” breakers to get more space, or install a subpanel for new kitchen circuits. Check with your lo cal building department for allowable subpanel locations.

First you must determine whether your home’s electrical system can handle all the new circuits. If you aren't adding any major appliances such as an electric range or dryer, and your home’s present service is properly grounded and at least 100 amps, it should be able to handle the new kitchen circuits. Otherwise you may need to upgrade the service entrance. The National Electrical Code has formulas for sizing a service entrance based on the anticipated electrical load, but as a rule of thumb a home with no electric heating or major electrical appliances (range, dryer, water heater) should need no more than 100-amp service; one major appliance, 125 amps; two major appliances, 150 amps; and electric heating, 200 amps or more.

Running multiwire circuits. Some codes allow two 120-volt circuits that are close to each other to be wired on the same three-wire cable, such as a dishwasher and garbage disposer.

The black wire is the hot leg for one circuit, the red wire is the hot leg for the other, and the neutral wire serves both. Each hot leg has its own circuit breaker; handles must be connected to turn off both simultaneously.

Pictured below are receptacles along a kitchen counter alternately wired on different circuits, using the same three-wire cables. In some cases, local codes may require that the white neutral wires be connected together and joined to the receptacle with a short pigtail.

Typical circuit wiring for a kitchen


• Lights: Kitchen, porch, and family room, 15 amp or 20 amp

• Small appliance, 20 amp

• Small appliance, 20 amp

• Range and oven: 20 to 50 amp

• Dishwasher 20 amp

• Garbage dispose 20 amp


• Light

• Switch

• Outlet

• Circuits

Typical circuit requirements for a kitchen

Multiwire circuit: The second outlet is wired with red wire, From source, The first outlet is wired with black wire, The third outlet is wired with black wire

Installing electrical boxes. Following your working drawings, install an electrical box for every switch, light, receptacle, and fixed appliance. Common practice is to center switch boxes 48 inches above the floor, wall outlets 14 inches above the floor, and over-counter outlets 42 inches above the floor. You can adjust locations as needed, however; you might raise outlet boxes to clear a tall backsplash behind the counter, or lower a box to conceal it behind a slide-in range.

Running electrical cable. Codes al low nonmetallic sheathed cable (Romex) in most installations. Use #12 for all 20-amp circuits and larger sizes for 240-volt circuits. Observe the same rules for running cable in a kitchen as in any other room, such as stapling it every 4½-feet and within 8 inches of plastic boxes and 12 inches of metal boxes. Many local areas don't allow wiring to be run horizontally through exterior wall studs; it must be run under the floor and brought up through the sole- plate for each outlet.

Specialty wiring for kitchens. Most kitchen wiring is straightforward, but some unique situations require special attention. E.g., if you are wiring more than one smoke alarm into the house current, link the alarms with three-wire cable (plus ground wire). The extra wire makes it possible to coordinate them so that all alarms will sound whenever one is activated.

Electrical boxes for some fixtures — range hoods, island outlets, and other cabinet outlets — can't be installed until after the walls are covered and cabinets placed. For rough wiring, simply run the cable to the general location and leave a generous length for completing the run when walls and cabinets are finished.

Although the disposer and dish washer must have separate circuits, many codes allow them to be wired with a single three-wire cable connected to a duplex receptacle under the sink. Isolate the two halves of the receptacle by breaking the external tab on the hot side and wiring the top half with the black conductor from the three-wire cable, and the bottom half with the red conductor. Both halves share the white neutral conductor. At the circuit breaker panel each black or red wire has its own 20-amp breaker, but the handles must be bonded so both breakers are off whenever one is tripped.

Kitchens need plenty of light, but not all the time. Use multiple switches to separate task lighting from general lighting, and dimmers to create pleas ant effects.

A freezer circuit should have some means of warning you if the breaker has been tripped. Most freezers have a light on the front that tells you the electricity is on. If yours does not, install a frequently used light on the same circuit as the freezer; in this way it will be immediately apparent if the circuit is dead.

Other wiring needs may include telephone cables, speaker wires, computer connections, telecom wiring, and low-voltage switch loops for operating fixtures in other areas of the house.

Finishing Walls and Ceiling

The walls and ceiling of a kitchen are insulated and covered in the same fashion as other rooms. Apply poly ethylene sheeting over the insulation to eliminate potential damage from water vapor.

Installing wallboard in a kitchen is more difficult because of all the cut outs for plumbing, wiring, and mechanical devices. Order a few extra sheets. If you are patching new wallboard into old wallboard or plaster, cut the old material back to a corner, door, window, or other feature to make the joint less obvious.

Most baseboard and other trim can be installed at this point, except where it abuts cabinets and built-in appliances.

Although special vinyl paints are often recommended for sealing fresh wallboard, a durable alkyd primer is better for sealing wallboard in kitchens, and it also creates sufficient tooth for oil-based finish paint. The final painting can be done after cabinets have been installed, although it's easier to do before.

Completing the Kitchen

Install cabinets, flooring, countertops, plumbing fixtures, appliances, and electrical fixtures the same as in any new kitchen.

If you are having the countertop fabricated at a shop, don't take final measurements until framing is completed and , ideally, finish wall applied. If possible, make the shop responsible for taking field measurements. If your plans don't specify them, make decisions about edge de tail, corner angles, and backsplash height. If you want the shop to install the countertop, be sure the sink, cooktop, and other built-in appliances are on site so the installers can make accurate cutouts. If you are installing the countertop yourself, you can make cutouts with a scroll saw. You may need to install a 2 by 4 ledger or other support on the back wall at cabinet height where sink and range cutouts are located and dish washer is installed; this will support the countertop where there is no cabinet backing.

Next: Bathroom Additions

Prev: Finishing the Interior

Top of Page  All Related Articles  Home