Installing the New Bathroom (Finally!)

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With an idea, a plan, and the methods in this guide, you can install the plumbing in a whole new room, You will need to size and frame pipes and fixtures and may need to cut through old walls, Here’s how.

This section will help you to plan and install a new bath room, either in an addition or in an existing room in your house. Because it has the most fixtures—including a toilet, which presents special problems in drainage and venting—the bathroom is the most complex plumbing installation in your house. If you can install a new bath room or remodel an old one, which is sometimes more difficult, you will find that the steps are very similar for installing a new kitchen, laundry room, or wet bar.

Two checks of new plumbing are required by law— approval of your plans when you apply for a building permit and inspection of your work before it's covered. Not only will this inspection contribute to your health and safety, but it should also reassure you if this is your first attempt at installing plumbing.

Planning a New Installation

In your initial planning, you may want some professional help. You can either have a builder or architect do the planning for you, with the understanding that you want to do the work yourself, or you can arrange to have a professional go over your plans. Check with your local authorities to see how much detail is required in the plan you submit for your permit.

Surveying Your Plumbing System

You may have a very specific idea of how and where you want your new bathroom to be. But whether you plan to remodel or to add on a new room. the first step is to check over what you have now. Explore the plumbing systems in your house. Walk around the outside and make notes as to where pipes enter and leave. Check the roof to see where the vent pipes are. Look into the crawl spaces under the house, into the basement, and into the attic to familiarize yourself with the piping that's visible and to get a general idea of the location and size of pipes hidden within walls, floors, and ceilings.

Design the kind of bathroom you really want and install it yourself.

Find where the water supply line (house main) enters the house and where along its length it would be easiest to install a tee for water supply to the new bath room. Check your water heater to see if it will supply enough hot water for the new bathroom or if you will need another water heater for the new addition. If the old heater will suffice, check along the hot water main to find where it would be easiest to install a tee for the hot-water supply to the new bathroom.

Img_81 Where to Tap Supply Lines

To find the best place to tap existing pipes, follow them through the basement or crawl space and trace them through the walls until you find where they are both accessible and as close as possible to your new installation.

The most important consideration in bathroom plumbing is the location and size of the existing soil stack. You will probably find it in the wall behind the toilet, in a closet, or beneath a stairway. There should be a clean- out plug at the base of the soil stack. Also note the location and size of the house drain—the large horizontal pipe that goes from the bottom of the soil stack to the sewer. A new toilet will usually drain directly into the soil stack or have its own secondary soil stack that connects to the house drain. If there is adequate crawl space, the toilet can be served by a 3-inch branch off the main drain and a 2-inch vent of its own.

The cost of the plumbing and materials and the amount of labor to install the new bathroom can be kept at a minimum by carefully planning the room’s location and layout. If the fixtures in the new bathroom can be located on the opposite side of a wall of an old bath room, back-to-back with the existing fixtures, and if the existing soil stack is of adequate size, you have an ideal situation. The amount of new plumbing will be minimal. The next-best situation is to have the new fixtures on another nearby wall and the toilet within a few feet of the existing soil stack. As long as they are vented properly, other fixtures can be quite a distance from the soil stack, but, depending on local codes, the toilet must be within 5 or 6 feet or have its own branch drain and vent.

Because most existing bathrooms are already backed up against a kitchen or another bathroom (for just the reasons mentioned here), it's unlikely that you will be able to place your new bathroom in such a position. In most cases, you will need to add a new soil stack or branch drain for the new bathroom. The easiest place to put a new soil stack is inside a new wall, as close as possible to the house drain. A new branch drain can be installed under the floor and vented through a wall.

If the new bath is in an addition to your house, the stack, branch drains, and all the new supply lines can be built into the walls and concealed beneath the floor as in any new construction. If, however, the new bath room is going to be built within your present house, the new soil stack, as well as other drain and supply pipes, may have to be concealed by thickening existing walls, boxing them in, or hiding them in closets or cabinets. A stack can also be run up an exterior wall of a house and boxed in with siding to match the outside finish of the house. This should be done only in warm-winter areas where freezing is unlikely or if the stack will be well insulated against freezing.

Mapping out the Bathroom

Once you have decided upon the actual location of your new bathroom, you can draw up a plan. A scale drawing is essential to accurate planning. One good method is to use graph paper, marking ¼ or ½ inch to 1 foot. Although bathrooms come in many shapes and sizes, the recommended size for a family bathroom is 6 x 8 feet and the minimum size for a full bath with tub is 5 x 7 feet.

First, draw in the room walls and mark the exact location of any doors and windows. Do not plan to run DWV or supply pipes through windows or doors. Most doors open into a room, but you can design the door to open out or to slide into a wall.

Back-to-Back Bathrooms: New bathroom; New double tee with two side outlets; This new bathroom is connected back-to-back with the existing bathroom on the second floor of the drawing.

A New Nearby Bathroom: The new bathroom isn't back-to-back with the existing one, but close enough so the new toilet is within a few feet of the stack.

A New Bathroom on a Branch Drain: 2-inch drain for shower

Next, mark the location of the soil stack. The locations of the other drain pipes and the supply pipes will be determined by the placement of the soil stack, structure of existing walls, and location of the fixtures. Pipes can be hung under first-floor joists in the basement or crawl space. Supply pipes can also be hung on top of ceiling joists in the attic. Between floors, try to plan your installation so that pipes can run the same way as the joists and lie between them.

The size and shape of bathroom fixtures can vary considerably. Once you have the measurements of your new bathroom, visit a couple of bathroom showrooms and decide on the fixtures you would like to have. To determine the exact location of your fixtures, you can cut out templates (scale models) and move them around on your drawing. One of the most important parts of planning fixture locations is allowing sufficient space for easy access, cleaning, and repairs. Although the plumbing fixture clearances in your local code may vary some what, you should plan for approximately the following clearances:

• Toilet: The minimum distance allowed from the center of the bowl to a wall or partition is 15 inches and to a bathtub, 12 inches. The minimum clearance from the front of the bowl to any wall or fixture is 21 inches.

• Lavatory: Allow 4 inches from the side edge of a lavatory to a toilet tank or finished wall, 2 inches to a tub, and 21 inches from its front edge to any wall or fixture.

• Shower: Allow 24” from the shower stall to any fixture or wall. The minimum floor area required for a shower is 1,024 square inches.

Plan the location of branch drains from each fixture. All horizontal soil pipes should slope downward about ¼” per running foot. Never plan to install a major fixture, such as a toilet, upstream from a minor one. The toilet’s closet bend goes directly into the stack. The lavatory bathtub, and shower must all have traps.

Every fixture trap must be vented, either into the soil stack through the drain pipe—a process called wet venting—or through vent pipes joined to the stack above the other waste lines, which is called re-venting. According to the National Plumbing Code, a tub or shower that has a trap within 3½ feet of the soil stack or a lavatory within 2½ feet of the stack can be wet vented. Check the plumbing code in your area for vent pipe specifications. The toilet will always require its own vent pipe.

Once the DWV system is planned, you can map out your hot- and cold-water supply pipes. If these will be connected to existing systems in your house, use the same route and openings as much as possible, Supply pipes should be located at least 6 inches apart and , although it isn't required, can have the same slope as drain piping. On your drawing, mark the exact locations of the faucet hookups—with the cold water running to the faucet on the right and the hot to the faucet on the left.

For both the DWV and supply pipes, allow enough space for pipe insulation if you live in a cold climate. An alternative is to cut 3- to 4-inch openings in the existing foundation to allow warm air to circulate from the basement into the crawl space beneath the new bathroom.

If a new water heater is needed, decide where it will be located. For a gas heater, determine the location of its flue pipe and how the heater will be enclosed and vented.

Fixture Clearances

Fixture Venting

Choosing the Pipes

Carefully choose the kind and size of pipe you will use for each part of the installation. We recommend ABS pipe for all of the DWV system because it's so easy to work with. Even if the existing system is copper or cast iron, ABS pipe can be connected to it easily. The size of DWV pipe is regulated according to fixture units (one fixture unit represents a waste flow of one cubic foot per minute). The soil stack will be 3 to 4 inches in diameter and most branch drains 1½” or 2”. Although the table lists pipe sizes according to the National Plumbing Code, you should check your local codes as well. Use the smallest size your code will allow. The code also sets a maximum length for drain pipe to run from a fixture to a stack, depending on its diameter:

DWV Pipe Length Limits


Distance to stack







The size of the vent piping is determined by the maximum fixture unit load, the length of pipe, type of fixture, and diameter of the soil or waste stack the vent pipe serves. Again, check your local codes for specifics. As a rule of thumb, the diameter of a vent can't exceed the soil stack diameter. The vent diameter can't be less than 1¼ inch or less than half the diameter of the drain it serves, whichever is larger, A vent stack serving a toilet must be at least 2 inches in diameter.

Vent pipe

















For supply piping, we recommend either copper tubing or plastic pipe. Copper is accepted by all codes and can be connected to any existing system. If you will be installing a shower stall, plan to use flexible copper tubing for the supply lines. Plastic water supply pipe is approved in some areas and not in others.

Comparing Drainage and Supply Fittings



Installing pipes in new construction is a matter of doing the various jobs in the right order and making sure the framing accommodates the piping and fixtures. If you have carefully planned your work, you should be able to proceed through the following stages step by step.

Assembling the DWV System

Once the foundation has been poured and the posts and girders are all in place, you can do the initial plumbing.

Some plumbers like to wait until the floor joists are in place, too. The floor joists in the bathroom must be set properly to allow room for the pipes to go up into the wall and to avoid the need for cutting through them when installing drain pipes for the tub, shower, and toilet. This means that a joist set parallel to a wall should never be placed directly under the wall. When joists are parallel to the long side of a bathtub, they should be doubled under the outside edge (see drawing).

At this stage, install the first 5 or 6 feet of soil stack with a cleanout. The soil stack must be as close to the toilet as possible. If the building drain and soil stack are of different sizes, you will need an adapter or reducer to connect them. Wait to extend the rest of the stack until after the framing of the room is complete.

Ill-84b Placing Joists Beneath a Bathtub:

Now locate the center of the hole for the toilet drain and cut a hole slightly larger than the fitting that will go through it. The closet flange under the toilet will connect to a closet bend that will turn toward the stack. If the fitting does not provide complete support to the soil pipe, you may need to build a support for the stack clamps.

Start assembling the drain pipes at the toilet drain. Suspend the closet bend from the joists or from nailed- on braces. Then work backward to it from the building’s drain line in the wall or floor. Horizontal DWV pipe must be supported at specific intervals as designated by your code. The drains for the tub and /or shower and the lavatory can also be put in place. Put in any branch tees for drains and revents as needed. Stub out all drains as they can be fitted with fixture traps after the walls have been installed.

Joists parallel to a wall allow pipes and wiring to enter from below.

Sample Pipe: Sizes for Bathroom Fixtures

Fixture; Supply; Drain units pipe

Double joists beneath the outside edge of a bathtub strengthen the floor.

A drainage fitting’s 1

Diameter is the same as pipe.

A supply or vent fitting’s diameter is larger than the pipe.

If you are installing a bathtub or lavatory with an overflow, check your local code for regulations The waste pipe must be designed so water never rises in the over flow and must be connected on the fixture side of the trap.

The main drain for a new toilet will have to be vented out the roof. Drains from the tub and lavatory can probably be wet vented.

Running Supply Lines

Run the hot- and cold-water supply lines from their source and extend them upward to a few inches higher than they will eventually be stubbed of f. Follow the rough-in dimensions specified for each fixture (see the drawings).

Make sure to keep the pipes at least 6 inches apart, In stall the main line runs first and then the branch runs, supporting horizontal pipe at intervals of 4 to 10 feet to minimize movement from hammering and temperature changes. At the point where branch runs to fixtures come through the wall, install tees. Above each tee, install a 12-inch length of capped pipe for an air cushion chamber, if required.

Once you have completed the rough plumbing (the inside-the-wall work), you must have your work inspected by a local authority. Be sure to arrange to have this done before you close the walls or you will have to open them up again. You may also find that a pressure test is required.

Rough Plumbing Dimensions: Centerline; counter top; Shower stub; Shower; Faucets; Toilet; Lavatory; Bathtub

Framing Pipes and Fixtures

When the joists and subfloor are in place, build the wall framing around the pipes. Build the wall enclosing the soil stack with a 2 x 6 or 2 x 8 sole plate, nailing 2 x 4 studs in place flat against the edges of the plate.

In addition to accommodating the framing of your new bathroom to the pipes, you must provide for the attachment of the fixtures:

• Install a 1 x 8 board across the studs behind the lavatory if it's to be wall-hung, and notch the 1 x 8 into the studs so it's flush. For most fixtures, the distance from the unfinished floor to the top of this board will be 32 inches. Of course, you can vary this distance according to the height of the people using the fixture.

• Install a 1 x 4 or 1 x 6 board across the studs to support the shower head, notching the crosspiece in so it's flush. The shower head will be attached to its midpoint—usually about 73 inches above the floor.

• Framing for a bathtub should include support blocks for the side and ends of the tub that go against the wall and blocking at the rim for drywall nailing. If you need to make room for the pipes at the head of the tub, measure up the wall the height of the tub and saw out the stud closest to the center of the tub. Insert a 2 x 4 between the joists, nail it in place, and cut two vertical studs to support it. Or you can nail a 2 x 4 to the studs to support the tub flange, as shown in the drawing.

Any handrails or grips around the tub or toilet also need 2-inch blocking between the studs.

• For the medicine cabinet, you will need headers at the top and bottom and vertical side nailers. A typical cabinet fits into a 16 x 22-inch opening between the studs, but you can cut out a section of stud to place the cabinet where you want it.

Thickened Wall to Accommodate the Soil Stack: To make a wall thick enough for the soil stack, use 2x6 or 2x8 lumber for the plates and set the studs flat against the edges. If you want a handrail, set a 1x6 board into the studs beside the toilet to hold the rail.

Toilet Framing: You are allowed to remove part of one joist if is in the way. You must secure the cut joist to adjacent joists with headers. Soil; Headers; Shower support

Framing for Bathroom Fixtures: Headers and framing for medicine cabinet; A shelf.

Finishing the Job

Once the framing for the pipes and fixtures is complete, add elbows and stubs to the drain and supply pipes so they will extend through the finished wall in the proper position (see drawings). Install the bathtub and /or shower at this time, too. Check your local code to see if it requires you to provide access to the supply and drain pipes serving your tub. You can usually install an access door in a closet or crawl space.

When the framing of the new room is finished, including the roof, extend the remainder of the soil stack and any other vents to their proper termination 12 inches above the roof line.

Now you can install the drywall or paneling and any built-in cabinets. The final step in the plumbing is the installation of supply stops for each fixture, faucets, shower stall, lavatory, and toilet.

Ill-87 Exposing Pipes

1. After making test holes and finding the pipes, use a tape measure to find and mark the position of the closest studs.

Marks at the edges of studs

2. Outline the area you’ll need to work, drill starter holes at each corner, and use a knife or keyhole saw to cut the opening.

Extending Pipes

Installing fixtures in a room that already exists can pre sent more problems than starting from scratch. If you want to conceal all the piping inside the existing walls and floors, you will have to remove a lot of drywall or lath-and-plaster wall covering and pry up a lot of flooring. You will also have to cut, drill, reinforce, and maybe replace some floor joists and wall studs to accommodate the soil stack and drainage pipes. Because supply piping is quite small, in most cases it can be run alongside the drain pipes without additional damage to the existing structure.

Exposing the Pipes

Once you have found the existing soil stack, you can use it as a starting point to locate other pipes and fixtures hidden in the walls and floors. You can sometimes track the pipes by turning on the water, one faucet at a time, and listening for the flow with your ear against the wall. You may need to drill test holes to determine the exact location of the hot- and cold-water supply pipes. When you have located the supply lines, turn of f the water at the main shutoff valve and drain them through the lowest faucets before you cut an opening in the wall.

As close as possible to where you plan to install your fixture, carefully knock a hole in the plaster or plaster board to expose the existing plumbing. Insert a steel tape measure into the hole on either side of the pipes until it contacts the closest studs. Mark the location of each stud edge on the wall and outline a large rectangle—about 3 feet high—to form a work area. Drill starter holes in each corner and use a keyhole saw or heavy knife to cut the opening.

Making Connections

Just as in new construction, you will need to connect each fixture to incoming hot- and cold-water lines and to the DWV system. Wherever possible, tap into existing pipes. Tapping the drain stack. First you must make sure that the stack is solidly anchored. If it slips even slightly, the roof seal at the top may break and cause a leak. To anchor the stack, install additional stack clamps above and below the section to be removed. (A stack or floor clamp consists of two perforated steel straps bolted together at the ends.) Put one strap to the back of the stack and the other in front. Tighten the bolts and support the ends with wood cleats nailed to the sides of the studs.

Tapping the Drain Stack

Measure the height of the new tee or tee Y fitting and mark it on the stack. Use a pipe cutter to cut along the marked lines. Slip the rubber sleeves of hubless pipe connectors over the cut ends, positioning them just above and below the pipe opening. Insert the tilting and slide each sleeve over a joint. Place the band clamps over each sleeve and tighten the screws. Leave the support clamps in place.

1. After installing stack clamps, mark the existing stack where it must be cut to insert the new tubeless fitting; Floor or stack clamp.

2. Use a soil pipe cutter to remove the marked section.

Tapping supply pipes. Procedures for connecting fixtures to supply pipes vary according to the kind of piping that exists. In all cases, you’ll want to install a tee, and if the pipe you want to use differs from the existing pipe, an adapter as well.

If the existing pipe is threaded, iron, or brass, you’ll have to use a wrench on the fitting to which it connects. This may involve cutting more than one wall opening.

You’ll have to cut the pipe; unscrew it from the fittings on each end; and install three pieces of pipe, the new tee, and a union.

If the existing pipe is copper or plastic, you can just cut out a section of pipe and sweat or cement the tee in place. The tee can be installed with or without slip fit tings, depending upon the rigidity of the existing pipe (see drawings).

Once the tee is in place, install an adapter if it’s needed and extend the piping to the location of the new fixture you want to install.

Tapping Supply Lines; Threaded pipe; Plastic or copper pipe

To tap threaded iron or brass pipe, you must have access to fittings at both ends of the piece you want to cut. If they aren't visible, you must cut other holes in the wall to find them.

Fittings - Vent pipe

Hot and cold Supply pipes

Loose or flexible pipes



Pipe extension

Tight or rigid pipes: Slip fitting

Pipe extension—Slip fitting

Installing a New Bathroom

Closing the Opening

In all new connections, leave the wall open for a couple of days to check for leaks before you close the opening. Alter you have checked your connections, nail cleats against the studs on either side of the opening. Cut a piece of plasterboard to fit the opening and cut slots in the board to fit around the pipes. Nail the plasterboard to the cleats and then close the slots with strips of plasterboard, taped smooth against the wall. Or you can install the plasterboard before you make your connections to the fixture, which will allow you to cut round openings that will fit the pipes.

Closing the Opening

In most cases, you will need to run a short length of pipe from the fitting through the wall surface. Mark the replacement plasterboard and drill holes for the tubing or pipe, using a wood bit or hole saw. You can patch around the pipe with plaster or taping compound; Install a chrome-plated escutcheon to hide the hole edges.

2x4 cleat

1. Nail cleats to the studs on each side of the opening.

2. Cut plasterboard to fit the opening and drill holes or cut slots for the pipes to come through. Nail the panel to the cleats and seal the edge with drywall tape and patching plaster.

ill-91 Back-to-back Sinks

Supporting Fixtures

Each fixture will need to be supported, just as in a new installation. This means that to install new fixtures in an existing structure, you will need to open up the wall or floor. Because of its size, install the bathtub first, remembering to leave access to the plumbing at the head of the tub if your code requires it.

When installing a toilet in a room not originally de signed for it, you may find that you can't place the closet bend between the joists. If you must remove a section of joist, cut of f the end—never a piece from the middle. Then securely fasten the cut joist to the joists on either side with a header, as shown. To be safe, shore up the floor before starting this process.

Adding a Lavatory

You may be able to extend piping from an existing fixture to serve a second fixture. There are several ways to do this, but one precaution pertains to all of them. Make sure the new drain pipe enters the existing stack at a point low enough to make the waste flow downhill, but not so low it will create suction on the new fixture’s trap.

(See below for the maximum distances drain pipes can travel from the fixture trap to the stack.) Also, check your local code to be sure a separate vent pipe isn't required.

Side-by-side sinks. To connect a second lavatory to one already in the room, you can make all the connections outside the wall. Attach the new fixture so that its drain hole is no more than 30 inches away from that of the existing sink and no more than 6 inches higher—al though the new drain must start somewhat higher than the old one to provide some slope. Cut the existing sup ply lines and install tee fittings to supply water to the new sink. Do the same for the drain line. Remove the tailpiece of the existing fixture and install a slip-joint tee above its trap. Connect this tee to the drain holes of both fixtures with a tailpiece for the existing sink and a tailpiece and 90-degree slip elbow for the new sink. Remove the existing shutoff valves, install tees behind them, and re place the existing shutoffs. Then run piping from the tees to the shutoff 5 of the new sink, Sinks connected through a wall. If you want to connect a new lavatory to an existing one in an adjacent room, you will need to open the wall to extend the supply and drain lines. If the sinks will be back to back, the drain and supply lines should be kept as short as possible. Re place the old stack fitting with a sanitary cross (which has no internal ledges that trap waste), Make the supply connections by installing new tee fittings on the existing supply lines and run pipes to the shutoffs on the new fixture.

Old lavatory. New lavatory. New sanitary cross fittings

Side-by-Side Sinks

If the new sink will not be directly behind the old one, you will need to extend the supply and drain lines along the wall. To run a drain pipe along a wall, use a 90-degree elbow and a spacer. Temporarily support the pipe with pieces of lumber or bricks until you connect the pipe. If the pipe extends along the wall for more than a few feet, use metal straps to anchor it to the wall.

Concealing Pipes in Existing Walls

To hide plumbing inside a wall or between a ceiling and the floor above, there must be enough clear space for the pipe and the fittings. Two-inch cast iron pipe and fittings (4 inches wide) will not fit inside a standard wall made of 2 x 4 studs (which are 3½ inches wide). This same wall, however, has plenty of space to contain 2- inch plastic or 3-inch copper pipe and fittings.

Because plastic, copper, and threaded iron pipe can be cut to virtually any length and the fittings placed wherever you want them, it's possible to plan your job so a length of pipe without fittings goes through an especially narrow area. You can put on fittings where more space is available.

If an existing wall has too little space for the piping that must go into it, enlarge the wall by setting new studs against the old ones and making the wall thicker. Even a 6-inch or larger addition to the thickness of an interior wall is difficult or impossible to detect once the wall surface is replaced and painted.

When running pipes horizontally inside a stud wall or across joists in a floor, you must drill or notch the studs or joists. In order not to weaken the wall, you may have to set new studs next to the old and thicken the wall even though there is room enough for the pipes.

Here are some regulations based on national building codes to prevent weakening the structure of your house too much:

• Do not notch a stud deeper than one third of its thickness unless you reinforce it with a steel strap.

• Do not notch deeper than one half of the stud, even if

you do reinforce it.

• Never notch a joist in the center half of its length. Make

any notches in the quarter of the length at each end.

• Never notch deeper than one quarter the height of a joist and always reinforce the notch with a steel strap or 2 x 2 board.

• Instead of a notch, a hole can be drilled anywhere along the length of a joist as long as it's centered from top to bottom and its diameter does not exceed one quarter the height of the joist.

Especially with small-diameter supply pipes, you can often minimize or entirely eliminate notching by lifting the flooring and cutting a groove in the subfloor. You may need to add furring strips between the subfloor and the flooring, as shown in the drawing.

Concealing Pipes in the Floor: Existing lavatory; New slip-joint; tee; New slip-joint elbow 30” or less

Furring strips Finished floor

Thursday, January 26, 2017 19:45 PST