Plumbing codes can be confusing. To make sure your DIY renovation is up to code, check out this guide to common plumbing codes, including how to purchase the right fittings, checking for leaks, and more.

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Plumbing is the most complicated aspect of most bathroom and kitchen remodeling projects. To prevent dangerous and unhealthy conditions, plumbing must conform to building codes. The National Uniform Plumbing Code applies generally to the entire country. You must also follow local codes, which could be more stringent. When planning your kitchen or bathroom 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 before you begin. Then follow these guidelines to make sure your remodel abides by the proper plumbing codes.

man adjusting plumbing underneath pedestal sink basin
Credit: Jay Wilde

Common Plumbing Codes

Common codes mainly focus on venting. After all, drainpipes that are not properly vented will run sluggishly and could release noxious fumes into the house. Here are some other important plumbing code considerations to keep in mind during your remodel:

  • Fixtures must not be placed too close together. This is critical in a bathroom, where space might 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 might 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 the pressure is low, you might need a booster pump. Where pressure is too high, you might need a pressure-reducing valve.
  • The installation of plumbing must not weaken the structure of a house. The inspector can 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

Adhere to these plumbing code requirements to ensure your kitchen or bathroom renovation goes smoothly.

correct slope for drainpipe diagram illustration

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 might call for careful calculations. Codes might require that vent pipes slope 1/8 inch per foot. Some codes allow level vents.

applying purple primer to join PVC pipes to prevent leaking

Use Purple Primer

Pipes that are glued without primer eventually will leak. Apply primer when joining PVC pipes to ensure a secure hold. Some plumbing codes require you to verify that primer was used. Choose a purple-colored primer ($8, The Home Depot) so the inspector can quickly tell that the pipes have been sufficiently primed.

various PVC fittings, tape measure and marker

Purchase the Right Fittings

List fittings in detail on your plumbing 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.

drainpipe through bored holes in doubled joists

Avoid Cutting Notches in Joists

Cutting a notch in a joist greatly weakens it. 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 will likely need doubled joists.

plumbing with cleanout installed opposite branch drain line

Install Cleanouts

A drain cleanout provides a convenient access point to a pipe. Plumbing codes call for cleanouts at various points so drains can be easily augered in case of a clog. You can simply remove the cap to access the blockage or debris inside the pipe. To be safe, install a cleanout whenever you tap into a drain line unless there is already one nearby.

testing for leaks in plumbing with inflatable drain plug

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.

open access panel covering plumbing valve inside wall

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.

adding dielectric union transition fitting joining pipes

Use the Correct Transition Fitting

When changing pipe materials, use the correct transition fitting. Without a dielectric union (shown above), 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.

ball valve in old galvanized pipes

Replace Old Gate Valves

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

water hammer arresters for washing machines

Consider Water Hammer Arresters

Water hammer arresters might be required for appliances such as a washing machine. Supply pipes could need to be cushioned wherever they run through or against a framing member. This helps prevent pipes from shaking or clanging against each other when the water flow suddenly stops. A water hammer arrester ($13, The Home Depot) creates a cushion of air that helps absorb the shock.

corroded shutoff plumbing valve

Shutoff Valves

In addition to the main shutoff valve for a house, plumbing codes might 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, for example, will need replacement or repacking.

various approved clamps and stamps for securing pipes

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.

Plumbing Codes for Pipes

Make sure pipes are up to code by adhering to these guidelines.

diagram for determining supply fixture units for pipes

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).

diagram for determining supply size for distribution pipes

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. These fixtures require 3/8-inch tubes.

diagram for determining drain fixture units for plumbing fixtures

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.

diagram for determining drainpipe size

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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