Confused by plumbing codes? Not anymore. Find tips and information on common plumbing codes, purchasing the right fittings, avoiding cutting notches in joists, and more.


Plumbing is the most complicated aspect of most bathroom and kitchen remodeling projects. Plumbing must conform to building codes to prevent dangerous and unhealthy conditions.

The National Uniform Plumbing Code applies generally to the entire country. You also must follow local codes, which may be more stringent. When planning your project request information about local plumbing codes from your local building department. Have the plans approved before starting work and perform all work to the satisfaction of the inspector. Draw a detailed plan that includes a list of all materials.

Common Codes

Common codes mainly focus on venting. After all, drainpipes that are not properly vented will run sluggishly and may release noxious fumes into the house. But here are some other important code considerations:

  • Fixtures must not be placed too close together. This is critical in a bathroom, where space may be at a premium.
  • Determine the correct pipe sizes for drains, vents, and supply lines.
  • Determine the correct pipe materials. Most inspectors will accept rigid copper pipe for supply lines and PVC for drain lines.
  • To ensure adequate water pressure, you may need to replace an existing globe shutoff valve with a full-bore ball or gate valve that does not impede the flow of water. If pressure is low, you may need a booster pump. Where pressure is too high, you may need a pressure-reducing valve.
  • The installation of plumbing must not weaken the structure of a house. The inspector may require that you reinforce joists that have been cut to accommodate pipes. Other requirements include the use of fire caulking around pipes and placement of protective plates over pipes.

Other Important Plumbing Codes:

Correctly Slope Drainpipes

In most cases drainpipes must slope at least 1/4 inch per running foot. Running a drain across a room that does not have a basement or crawlspace may call for careful calculations. Codes may require that vent pipes slope 1/8 inch per foot. Some codes allow level vents.

Use Purple Primer

Use purple primer when joining PVC pipes so the inspector can quickly tell that the pipes have been primed. Pipes that are glued without primer eventually will leak.

Purchase the Right Fittings

List fittings in detail on your plan so you will be sure to purchase the right ones. Be sure to use special drain fittings, such as a closet bend, so wastewater can flow smoothly. Inspectors will have specific fitting requirements for different fixtures.

Avoid Cutting Notches in Joists

Cutting a notch in a joist greatly weakens it. So whenever possible bore holes through joists instead. This calls for careful work as holes for a drainpipe must be at slightly different levels so the pipe will slope. Whether notched or bored long spans may need doubled joists.

Install Cleanouts

Codes call for cleanouts at various points so drains can be easily augered in case of a clog. To be safe, install a cleanout whenever you tap into a drain line unless there is already one nearby.

Check for Leaks

Once drain lines are assembled, an inspector will probably test to make sure they do not leak. Some inspectors will simply pour water through the pipes. Other inspectors require that the line be plugged with an inflatable drain plug and the system filled with water.

Install an Access Panel

Valves, fixture controls, cleanouts, and compression pipe fittings must not be covered by a wall or floor surface in case you need to work on them in the future. If necessary, install an access panel. The most common location for an access panel is behind a tub or shower.

Use the Correct Transition Fitting

When changing pipe materials use the correct transition fitting. Without a dielectric union (shown), the joint between galvanized and copper pipe would quickly corrode. Use the approved fitting when changing from plastic to copper, cast iron to plastic, and ABS to PVC.

Replace Old Gate Valves

Old plumbing usually can remain; however new plumbing needs to meet code. If old galvanized pipes and gate valves cause low water pressure, you may need to change them in order to supply new pipes with enough pressure. Here a ball valve has replaced a gate valve.

Consider Water Hammer Arresters

Water hammer arresters may be required for appliances such as a washing machine (shown). Supply pipes may need to be cushioned wherever they run through or against a framing member.

Shutoff Valves

In addition to the main shutoff valve for a house, codes may require shutoff valves that control a portion of the house. A hose bib should have an interior shutoff valve. All faucets and toilets must have individual stop valves. This corroded old valve will need replacement or repacking.

Use Approved Clamps or Straps

Use approved clamps or straps to secure pipes. According to most codes copper supply pipe must be supported every 6 feet, galvanized or black steel pipe every 12 feet, PVC or ABS drainpipe every 4 feet, and cast-iron pipe every 5 feet. To be safe install more supports than are required.

Make Sure Pipes are Up to Code:

Branch Pipes

These pipes run from the distribution pipes to the fixtures. As a general rule you can run 1/2-inch pipe to most fixtures; run 3/4-inch pipe to a hose bib or a water heater. Different fixtures place different demands on supply pipes. Each fixture has a demand rating based on fixture units (see chart).

Supply Tubes

These are the flexible lines that run from the stop valve to a faucet, fixture, or appliance. As a general rule run 1/2-inch supply lines to all fixtures except toilets and bathroom sinks, which use 3/8-inch tubes.

Sizing Drainpipes

Use this chart to count the number of fixture units that will be connected to a drain line and for the minimum drainpipe size. If a toilet connects to a drainpipe, the pipe must be at least 3 inches. Check local building codes.

Fixture Trap Size

A bathroom sink uses a 1-1/4-inch trap. Showers and floor drains use 2-inch traps. All other fixtures and appliances use 1-1/2-inch traps.


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