Should a shower drain have a P trap?

A P trap is a curved piece of pipe that is installed below drains in sinks, showers, tubs and other plumbing fixtures. The purpose of a P trap is to prevent sewer gases from entering the home while allowing water and waste to pass through. P traps get their name from the P shape the pipe makes below the drain. While P traps are required by code under most sink drains, whether they are necessary below shower drains is a common question among homeowners.

What is the purpose of a P trap?

A P trap serves two main purposes:

• It blocks sewer gases from entering the home. The curved shape traps a small amount of water which creates a seal that prevents gases from passing through.
• It allows water and waste to drain freely. The curved shape does not impede drainage.

Without a water seal in the trap, gases from the sewer system could enter the home. These gases can include methane, hydrogen sulfide (which smells like rotten eggs), ammonia, carbon monoxide and other harmful substances.

Why are P traps used?

P traps have been used in plumbing systems for over 100 years. They are required by plumbing codes in most areas because they provide a very effective water seal to block sewer gases.

Some key reasons P traps are so ubiquitous include:

• They are self-sealing – No manual seals or flaps are needed. The water in the trap creates the seal.
• They require no maintenance – P traps have no moving parts and do not need to be adjusted or replaced over time.
• They adapt to temperature changes – As water warms or cools, the trap still maintains an effective water seal.
• They are difficult to siphon dry – Siphoning occurs when pressure changes in the plumbing system draw all the water out of the trap. P traps are shaped to minimize this.

The simple but clever design of the P trap has made it the go-to solution for blocking sewer gas for over a century.

Do all drains need P traps?

While P traps are required by code under most sink drains, tub and shower drains are a bit different. Whether a shower drain needs a P trap depends on a few factors:

• Type of shower – Free-standing showers far from other drains often require a trap. Enclosed showers share drainage so individual traps are not always needed.
• Main trap location – If the shower drain connects to a main drain stack with a wet P trap within a few feet, an additional trap may not be needed.
• Trap seal depth – Shower traps may need deeper water seals to compensate for rapid drainage.
• Vent location – Showers must connect to a properly vented drain line. Vents equalize pressures in the pipes.

So while most shower drains should have a dedicated P trap, the exact code requirements can vary. Many factors influence whether a shower trap is mandated.

Do showers need deep trap seals?

Showers and tub-shower combinations require a 2-inch minimum trap seal depth under the International Plumbing Code and Uniform Plumbing Code. The standard for other fixtures is 1.5 to 2 inches. The deeper trap is needed for showers because:

• Water drains rapidly – The deeper seal prevents siphoning.
• Shower traps are shared – Multiple drains use the trap so it should hold more water.
• Vents equalize pressure – Showers have larger vents which can siphon standard traps.

The deeper the trap seal, the more water is held in the trap curve to block gases. For showers, 2 inches is the minimum, but deeper 3-4 inch traps are recommended by many experts.

Pros of installing a shower P trap

There are several benefits to installing a dedicated P trap below a shower drain:

• Blocks sewer gases – A shower trap provides an effective gas seal close to the drain.
• Contains odors – It prevents smelly gases from the sewer lines entering the shower area.
• Allows proper drainage – The P shape does not impede water flow from the shower.
• Required by code – In many cases, a shower P trap is mandatory under the plumbing code.
• Peace of mind – Knowing sewer gases cannot enter living spaces through shower drains.

Having a functioning P trap on all shower drains provides an added layer of protection from potentially harmful sewer gases.

Cons of installing a shower P trap

There are not many drawbacks to installing a P trap under a shower, but a few things to note are:

• Costs more – Adding a trap adds cost for materials and labor.
• Takes up space – Traps take up a few extra inches under the shower.
• Needs occasional maintenance – If clogged, shower traps need to be cleaned.
• Potential for leaks – Improperly installed traps can leak.

Overall the pros of adding a shower P trap far outweigh the cons for most homeowners. But they do require a small investment and a little maintenance.

P trap installation tips

If adding a new P trap below a shower drain, keep these tips in mind:

• Use 1.5 inch tubular PVC or ABS for optimal drainage.
• Ensure the trap is vented properly to prevent siphoning.
• Install with the curve as close to the drain opening as possible.
• Maintain a 2 inch trap seal depth at minimum.
• Secure with slip joints – no glue needed.
• Check for leaks and make sure all pipe is pitched properly.

Proper installation is key to gaining all the benefits of a P trap without any drawbacks like leaks or blockages. Getting a professional plumber to install shower drains and traps is highly recommended.

Maintaining and cleaning shower P traps

To keep a shower P trap functioning properly:

• Check routinely for leaks – Look under the shower for dripping.
• Fill with water after long periods of disuse – Letting traps dry out can allow gas to enter.
• Clear clogs and blockages – Use a drain snake or plunger.
• Clean sediment – Disassemble and flush out built-up debris.

With routine maintenance like this, a shower P trap should provide years of reliable service.

Signs of P trap failure

Some signs that a shower P trap may be malfunctioning include:

• Sewer gas smell in the bathroom.
• Gurgling noises from shower drain.
• Water leaking under the shower.
• Drainage problems or frequent clogging.
• Visible cracks or damage to the P trap.

If any signs of P trap failure are noticed, have a plumber inspect and replace the trap if needed. Allowing gases to enter living spaces can lead to health risks.

Replacing a faulty shower P trap

Here are the steps for replacing a malfunctioning shower P trap:

1. Turn off water supply and drain the trap.
2. Loosen the slip nut connections with pliers or wrench.
3. Remove old trap and clean out drain opening thoroughly.
4. Install new 1.5 or 2 inch P trap and hand tighten slip joints.
5. Restore water supply and check for leaks.
6. Test shower drainage and check for sewer gas odors.

Always replace shower traps with the same size and type that was originally installed. Make sure all slip nut connections are tight.

Cost to install a shower P trap

The cost to add a P trap under a shower depends on a few factors:

• Plumbing layout – Ease of access to pipes affects labor time.
• Drain location – Moving the drain costs more.
• Trap material – ABS plastic is least expensive.
• Trap size – 1 1/2 inches is standard.
• Contractor fees – Plumbers may charge $50-$100 per hour.

The total costs can range from $150 – $450 on average. Hiring a professional ensures proper installation and code compliance.

Conclusion

In summary, P traps are highly recommended below all shower drains. They provide effective protection from sewer gases and proper drainage. The pros of installing shower P traps far outweigh the cons for most homeowners. With routine maintenance, they will provide years of reliable service. Checking local plumbing codes is advised, as some areas do mandate shower P traps. But even if not required, adding this simple plumbing fixture brings peace of mind knowing damaging sewer gases cannot enter the home.