Plumbing: Roughing a Half Bath

If you have an older home or a growing family, you could probably use another bathroom. A half bath often works well because it’s small enough to squeeze into your current floor plan. But even with a half bath, building an entirely new bathroom is a big project, involving carpentry, plumbing, electrical, drywall, tiling and other skills.

Space issues. Closets, pantries and portions of bed rooms are the most likely places to steal space for a half bath. At a minimum, you’ll need 30 x 66 in. (76 x 168 cm) of floor area if the fixtures are on opposite walls, or 48 x 54 in (122 x 138 cm) if the fixtures rest against the same wall. You might have to shift a wall or two to get the right dimensions. Some non-bearing or partition walls are simple to shift. Others—if they’re load-bearing or contain heat ducts, plumbing pipes and electrical wires—are best left alone.

Location issues. The main waste line is a 3- or 4- in. pipe called a soil stack when run vertically and called a building drain when run horizontally under ground. At a minimum, you’ll have to attach a 3-in. waste line from your new toilet to this main waste line. In a slab-built home, this main line can be difficult to find, because it runs under concrete.

Framing issues. Keep the subfloor intact and frame the new bath walls with 2x4s. If you have to frame a wall that contains the 3- or 4-in, waste lines, use 2x6s. The open space in your half bath might be too small for a normal inward-swinging door, so you may elect to install an outward-swinging or a pocket door. When you install the wall studs, leave space and access to run plumbing, electrical circuits, heat ducts, exhaust fan and blocking for things like grab bars and wall- mounted sinks.

Plumbing issues. If the toilet drain is over a joist, see if you can shift the toilet; cutting a floor joist can seriously weaken the floor and additional framing will be required. Another problem: Half-inch pipe can serve only two or three fixtures, so you might have to tap into a 3/4-in, supply line for the added fixtures.

Five Steps for a Top-notch Job

1. Slope all horizontal drain lines a mini mum of 1/4 in. per foot (2 cm per meter) and support pipe every 32 in. (80 cm).


2. Anchor flange with screws at finish floor height to provide a solid point for drain assembly.

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3. Tap into existing water lines and install supply lines for new bathroom. Run hot and cold for faucet and cold for toilet.

4.Stub out faucet supply lines above drain for pedestal sinks. Support cop per pipe with wood blocks or special copper strap.

5. Before connecting to main soil stack, rent pres sure gauge to pressure-test DWV system. With the system temporarily plugged, it should hold 5 lbs. (2.27 kg) for 15 minutes.

Half-bath plumbing and electrical rules

Codes vary, so confirm your plans with a local building inspector. Here are some generally accepted rules to follow:

  • Position a 2-in, vent to rise vertically from drain within 4 ft. (1 .2 m) of toilet flange.
  • Position a 1-1/2-in, vent to rise vertically within 42 in. (1 m) of a 1-1/2-in, sink trap.
  • Maintain uniform slope on all drain lines (see Step 1). Run sink and toilet vents vertically to a point 6 in. (15 cm) above overflow level of fixture. Slope horizontal vent runs back toward drain.
  • Whenever plastic or copper pipe or electrical wire pass within 1-1/4 in. (32 mm) of a framing surface, protect lines with protective steel plates. The bathroom should have its own 20-amp circuit.
  • Use a GECI-protected electrical outlet.
  • Provide a ventilation fan, vented to the outside, over the toilet.

Notching and Boring Rules

As you remodel, you can’t simply cut, notch and bore through structural members and expect your house to remain strong and your floors solid.

If you have solid wood joists, follow these rules to maintain structural integrity:

  • Holes must be at least 2 in. (5 cm) from top and bottom edges of joist.
  • Maximum hole size is one-third of joist depth.
  • Avoid locating holes and notches near loose knots.
  • The maximum depth of a notch at the end of a joist can’t exceed one-quarter of the joist’s depth.
  • Maximum notch depth in the outer third of a joist is one-sixth of joist depth.
  • Maximum notch length should be no more than one-third of joist depth.
  • Do not notch anywhere in the middle third of a joist along its length.


Smart shopper: Instant Hot-Water System

If the inconvenience and waste of water, energy and money that occurs while waiting for hot water to reach a fixture bothers you, install a re-circulating pump that brings hot water to your fingertips in seconds. The unit shown is compatible with most plumbing codes and requires only basic tools and skills. To work, a pump and controller unit are installed under the sink farthest from your water heater. This way, the system automatically works for any other sink or shower that runs off the main hot-water line.

The pump unit connects the hot-water line to the cold-water line. When activated, the unit pumps the cool water in the hot-water line into the cold-water line and back to the water heater. As soon as the hot water arrives, a temperature sensor shuts off the pump.

Last modified: Friday, 2007-11-02 23:42 PST