S Trap vs P Trap

S Trap vs P Trap 

When it comes to plumbing, selecting the proper trap for your bathroom or your kitchen is extremely important. Here, we will compare between the S traps and P traps, why the S traps are illegal in Australia and how to easily convert from an S trap to a P trap. No matter you are a homeowner or a professional plumber, this article contains all the information you might need!

What is an S Trap?

S trap is a plumbing fixture trap that is in the form of an “S”. This one is vented to an exterior to be able to retain a small amount of water to seal out sewer gases from the house. S traps were common in Australia and specifically in the housing developing before the period of the early 1990s.

However, S traps have since been prohibited in Australia since they pose a risk to human’s lives. Their design can lead to siphoning where water is pulled out of the trap with sewer gases pushing into your living spaces.

Are S Traps Illegal in Australia?

S traps are prohibited in Australia because they pose numerous safety and regulatory risks. Knowing the cause of this ban will assist homeowners and plumbers to make the right choices concerning the plumbing systems. Here are the key points explaining why S traps are prohibited:

  • Non-Compliance with Modern Plumbing Codes: S traps as used do not conform with set out in the Australian Plumbing Codes. The code other specifies that plumbing fixtures required to afford protection against the entrance of sewer gases into living space in matters of health and safety. S traps often fall short in this respect.

  • Siphoning Issues: Mechanism of Siphoning: S traps are especially vulnerable to siphoning – the forces in the water that hold the water seal of an S trap U bend, are pulled out by a rush of water or a negative pressure in the drains.

  • Health Risks: Whenever the water seal is breached contaminants such as methane and hydrogen sulfide contained in sewer gases find their way into homes and pose health risks to people.

  • Regulatory Prohibitions: The requirement of the National Construction Code (NCC) and the Australian Standard AS/NZS 3500 also does not allow the use of S traps in new plumbing systems. The regulations point toward the importance of implementing plumbing systems that will minimize the hazards of gas leakage substantially.

  • Historical Context: Older homes however used to employ the use of S traps. Nonetheless, improvements in pipes technology and recognizer of health hazards based their development of new and sophisticated designs such as p trap which are the most common in modem plumbing.

  • Increased Maintenance and Repair Costs: Some homes may use S traps than other types of pipe traps and this exposes them to more plumbing problems than their counterparts thus experiencing more frequent pipe problems. These costs are best avoided for the long haul, and one way of doing so is to upgrade to P traps instead.


  • Safety First: Governmental and non-governmental regulatory institutions’ chief consideration is the welfare of the general public. Through banning S traps, there are considerable losses of food hygiene potential accidents and health hazards from improper plumbing.

For More InformationYou can find detailed regulations and safety guidelines through the following government resources:

What is a P Trap?

To compare, it is crucial to note that While S traps resemble an S form the P traps are in the shape of a P. This design has a lower water-level rim-design which makes it easier for it to be less siphonic. P traps are used in most new systems of plumbing in Australia, and the P trap conforms to local standards of Australia.

Benefits of P Traps

  • Improved Safety: P traps are much more likely to provide a stronger water seal thus cutting down the chances of sewer gas breakout.

  • Ease of Installation: The disadvantage of a P trap is that it is slightly less flexible about the direction of flowing water, but this is a small compared to its benefits when it comes to versatility on plumbing.

  • Compliance: Soldering the P traps is crucial to conform with the present day building standards, thus the homeowners and other professionals might consider the upgrade important.

  • Reduced Risk of Clogs: P traps are different than other traps because the design of the pipes allows water to flow smoothly and with little chance of developing clogs in the long run. The result is low frequency of maintenance and low incidence of plumbing trouble.

  • Versatility in Application: P traps may be installed around any place where water is likely to flow, such as sink, bathtub, or toilet. This again comes handy in that they are fit for intermittent use, meaning that they can be applied on any kind of plumbing system, thus guaranteeing optimal installation.

  • Durability: There is a common use of P traps, and most of them are constructed from rather durable materials such as PVC, ABS or even metal. This means that the homeowners are capable of getting longer performance without having to replace them so often hence; more savings.

  • Ease of Maintenance: P traps are precise in their design so that they can easily allow access and maintenance. If a clog occurs then they can easily be disassembled and this means that plumbers will not spend much time clearing all the clogs without having to install the whole system.

  • Aesthetic Considerations: Besides their practical use, it can be noted that P traps can be selected from versatile types of material and can be finished to correlate with the stylistic look of modern sanitary ware facilities making a beautify addition to kitchens and bathrooms.

  • Noise Reduction: Overall, P traps are less noisy during operation as compared to S traps. An added advantage is that the design reduces the possibility of producing gurgling and any other noise commonly produced by drainages hence improving on the living standards.

  • Environmental Compliance: Eliminating vented fixtures corresponds with the general move towards the greening of plumbing systems. Due to their ability to decrease the chances of sewer gas breakout, and enhance system efficiency, they are generally healthier for the environment.

P Trap vs S Trap: Key Differences

Different types of traps used in plumbing systems do make some difference as far as the safety of the building is concerned, as well as the efficiency of the system. The sections below presents the adequate comparison table that will help to identify the differences between P traps and S traps.

P Trap

  • Design: Shape and Structure: These P traps are shaped round like the alphabet letter “p”. This design entails a level portion connected to the drain channel, which opens to a vertical pipe for adequate ventilation.

  • Siphoning Protection: Ventilation Connection: P traps are normally vented that is, they have a ventilation vent connected to them. This connection plays a big role in closing interactions within the drainage system meaning that the chances of siphoning where the water seal is easily realized are greatly minimized. In practical terms, it means that when there is a peculiar straining of water down the drain (for instance a large volume of water is washed down a sink) the vent prohibits the creation of vacuum pressure that sucks water out of the trap.

  • Efficiency: Greater Water Seal Preservation: P traps are designed to offer a better water seal that efficiently prevents a seepage of evil smelling sewer gases into homes. This increased efficiency is necessary for regulating IAQ indoors and giving occupants the assurance they need.

  • Legality: Regulations: P traps meet the requirement of the National Construction Code (NCC) as well as the Australian Standard AS/NZS3500, thus legal for use in new constructions in Australia. This compliance is as well beneficial in assuring the plumbing systems through the safe systems and efficiency and avert the homeowner from the avenues related to the legal implications on police on plumbing safety standards.

S Trap

  1. Design: Namely that Shape and Structure: S traps are literally S shaped. Although this design has been used in the past and is common today, its configuration results in problems on the modern systems.

  1. Siphoning Issues: - Vulnerability to Water Seal Loss: S traps are prone to siphoning because they lack the ventilation connection found in P traps. When a significant amount of water flows through the S trap, it can create negative pressure, which may suck the water seal out of the trap. This phenomenon can allow harmful sewer gases to escape into the home, posing a serious health risk to occupants.

  2. Efficiency: - Potential Dangers: Due to their susceptibility to siphoning, S traps are considered less efficient overall. The likelihood of sewer gas escape could lead to unpleasant odors and significant health concerns, making them a dangerous option for plumbing systems.

  3. Legality: - Prohibition in New Installations: S traps are illegal for new installations under Australian plumbing regulations, as stated in the NCC and AS/NZS3500. The ban aims to protect public health and safety by ensuring that modern plumbing systems use more effective designs that mitigate the risk of gas leaks.

Example of P Trap Use: In a modern kitchen sink installation, P traps are commonly used because they effectively prevent odors and sewer gases from infiltrating the home. The ventilation feature allows the system to function smoothly even during high water flow, such as when multiple dishes are rinsed simultaneously.

Example of S Trap Issues: An older home with S traps may experience persistent foul odors and complaints from residents about the smells in bathrooms or kitchens. If the home undergoes renovations, replacing the S traps with P traps could significantly improve air quality and compliance with current regulations.

Can You Still Buy S Traps?

While S traps are still available on the market, particularly in older homes, their use in new construction or renovations is prohibited under current plumbing regulations in many regions, including Australia. This prohibition is primarily due to safety concerns related to sewer gas escape and inefficient drainage performance.

If you currently have an S trap in your home, there is no legal obligation to replace it unless you are undergoing renovations or upgrading your plumbing system. However, it is highly advisable to consider replacing S traps with P traps for various safety and efficiency reasons. Upgrading can improve indoor air quality and comply with modern plumbing standards, ultimately protecting the health of the occupants and ensuring a more effective plumbing system.

How to Upgrade from an S Trap to a P Trap

Switching your plumbing system from an S trap to a P trap can be another major boost for improving safety and meeting current requirements. This upgrade can be done at the same time with the overall building renovation or as a separate plumbing work. Here are detailed steps to guide you through the process:

  1. Assess the Current Setup:

Evaluate Space Requirements: As a first step, consider the current plumbing of your home and evaluate adequacy of space for the installation of the P trap once work begins. P traps are usually designed different from S traps, and as such they more often than not requires more width horizontally. Look at the space under the sink or fixture and determine if the new layout will allow space for other plumbing fixtures in the same area.

Identify Accessibility: Make sure that the place is reachable for the removal of the S trap and replacement of the P trap. If such complicating factors as tight fitting or awkward angles are present then these may be an issue to the upgrade.

  1. Hire a Professional Plumber:

Importance of Professional Assistance: Replacing an S trap with a P trap is work that is best left to an expert licensed plumber. A professional plumber will know what the regulations are, local requirements such as the AS/NZS3500 or any other regulation and will ensure that the installation done meets the standard and requirement set in place.

Inspection and Recommendations: A licensed plumber can also run a check over your entire plumbing system, give further advice on other modifications that may be necessary and warrant that the change does not bring other issues downstream.

  1. Cost Considerations:

Estimate of Replacement Costs: The cost of replacing an S trap with a P trap is normally between 150 to 400. The last cost can be bigger or lower, depending upon the complexity of the installation and availability of the pipes for the plumbing, and rates that masters of plumbing demand in specific area.

Potential Additional Costs: Be prepared for potential additional costs if your plumbing system requires modifications or repairs beyond just the trap replacement. This could include replacing old pipes, enhancing venting systems, or addressing any pre-existing plumbing issues.

  1. DIY Option:

Evaluate Skill Level: While it may be tempting to attempt the upgrade yourself to save money, doing so is generally discouraged due to strict plumbing codes and potential legal ramifications. However, if you are a skilled DIYer with a solid understanding of plumbing systems, you may consider tackling the job.

Follow Local Regulations: If you choose the DIY route, ensure you follow all local regulations and building codes meticulously. Familiarize yourself with the correct procedures for installing a P trap, including venting and drainage requirements, as improper installations can lead to future leaks, clogs, or other plumbing issues.

Resources and Guidance: Refer to reputable plumbing resources or instructional guides to aid your project. Consulting manuals or online resources can provide valuable insights into the correct installation techniques and troubleshooting tips.

  1. Consulting Professional Guidance:

Always consider reaching out to local plumbing associations or the Building Institute of Australia for additional information and resources regarding plumbing qualifications and advice. They can provide further guidance on standards and best practices to ensure your plumbing system remains safe and efficient.

Upgrade Your Plumbing for Safety and Compliance

If you still have an S trap in your home, it’s time to consider an upgrade. Replacing your outdated plumbing with a modern P trap will not only improve the safety of your home but also bring your system up to code. Whether you need to install a P trap in your kitchen, bathroom, or toilet, professional plumbers can assist you in making the switch.

Want To further your career in plumbing?

Consider pursuing certifications or qualifications through reputable institutions. The Building Institute of Australia offers various programs such as, Certificate III in Plumbing designed to provide you with the necessary knowledge and credentials to succeed in the plumbing industry.

FAQ

  1. What are the risks of keeping an S trap in my home?

Answer: The biggest risk of an S trap is siphoning, which can cause the trap to lose its water seal. This allows dangerous sewer gases to enter your home, creating potential health risks and unpleasant odors.

  1. How do I know if my plumbing uses an S trap or a P trap?

Answer: To determine the type of trap, look at where the waste pipe exits. If the pipe goes through the floor, it’s likely an S trap. If it exits through the wall, it’s a P trap. A licensed plumber can also inspect your system for you.

  1. Do I need to replace an S trap if I’m not renovating?

Answer: You are not required to replace an S trap if you’re not renovating or upgrading your plumbing. However, it’s highly recommended to do so for health and safety reasons.

  1. Can I replace an S trap myself, or do I need a plumber?

Answer: While DIY replacements are possible, it’s recommended to hire a licensed plumber to replace an S trap with a P trap. 

  1. What should I do if I smell sewer gas in my kitchen or bathroom?

Answer: If you smell sewer gas in your kitchen or bathroom, it’s a sign that your trap may have failed, likely due to siphoning in an S trap. It’s important to contact a licensed plumber to inspect your plumbing system and, if necessary, replace the S trap with a P trap.

  1. Are there any alternatives to S traps and P traps?

Answer: While P traps are the standard, there are other types of traps, such as bottle traps and drum traps, which are used in specific situations. However, P traps remain the most common and reliable for residential and commercial plumbing systems.