The introduction of new guidance and mandatory testing for gravity drainage solutions in high-rise buildings will have an impact worldwide on system design.
With no real shake-up of the design standards since the 1960s, the launch of CIBSE TM70:2025 – Tall Buildings Drainage Design, which forms part of the new CIBSE Guide G, is a pivotal moment in high-rise design, setting new standards and testing regimes to provide safer solutions.
The Technical Memorandum (TM) highlights Fully Active (FA), which Aliaxis calls Active Drainage Ventilation (ADV) which uses the P.A.P.A.™ and Air Admittance Valves, as the best solution suitable for buildings up to 400 meters in height. The Technical Memorandum also introduces mandatory Drain Waste Vent (DWV) commissioning testing, aligning with realistic flow rates. It is the first guidance that actually tests the building drainage performance over and above the current tightness test.
David Thomas, Head of Technical Support Services at Aliaxis UK, explains why it has taken years of research to get to this point and why the new guidance, which is industry-led, will vastly improve the speed and accuracy of drainage system design, delivering high-rise buildings and skyscrapers that are healthier and safer places to be.
High-rise gravity drainage systems present a myriad of challenges, and getting the design wrong can have serious consequences. When air pressure becomes imbalanced, the results can be dramatic: negative pressure can suck water out of traps, leaving them dry and allowing foul odours and harmful pathogens to enter living spaces, while positive pressure can force air and waste gases back through the system, sometimes violently – the infamous ‘exploding toilet’ scenario. Behind these symptoms lies a critical health and safety issue that demands careful attention in design and ventilation strategy.
Infection risk
When a trap water seal blows out, micro aerosols can be expelled. If someone is sick in a building, pathogens such as SARS-CoV virus, COVID-19(SARS-CoV-2), Legionella or Norovirus, can be transmitted between floors in a tall building, creating the potential for an infection outbreak.
The trap seal acts as an integral part of the hygiene system in high-rise buildings and an essential barrier to minimise infection risk. To maintain system integrity, it is important to implement measures that stabilise and regulate these short-duration pressure events.
More than 30 years of research have gone into trying to resolve these issues, which is why, as structures get taller and taller, new guidance and testing was long overdue to ensure the provision of a healthy building.
Original data used to design gravity drainage systems and calculate flow rate was generated in the 1960s, and was based on a maximum height of 10 floors and this data is still being used today.
It is why the launch of CIBSE’s Guide G and its TM will make such a difference. This is the first guidance of its kind for high-rise buildings published in the world and will give designers, particularly Chartered Engineers, the tools to accurately design a gravity drainage system for high-rise buildings.
Aliaxis UK has been heavily involved in the research sitting behind the new Guide G and TM, using its Training and Research Centre, at the National Lift Tower (NLT), in Northampton. It is perfectly placed for such research, housing the world’s tallest drainage testing installation with a 75m soil stack, which can recreate 40 flushes within the system to test real-life situations.
The TM itself has undergone nearly 60 peer reviews, including input from our NLT team, who supported Heriot-Watt University in developing and defining the new commissioning protocol. It is why we felt it was important for Aliaxis UK to sponsor the launch of the new Guide G and TM event.
Extensive research
Heriot-Watt University has developed an innovative numerical model, AIRNET, which provides an accurate simulation tool for drainage systems.
Over the past three years, all 3,000 models and tables within AIRNET, which meet the new TM guidance, have been run through Aliaxis’ Training and Research Centre showing the simulations to be 98% accurate.
BS EN 12056-2 is the British Standard detailing technical guidance for the design and calculation of gravity drainage systems inside buildings. This standard is due to go under review and the new CIBSE TM is expected to be incorporated. The review could take two or three years, but it is worth noting that BS EN 12056-2 took 14 years to develop and was finally published in 2001.
The new commissioning test is also the first of its kind in the UK, as there has never been one for high-rise drainage, especially for system and design performance. Aliaxis UK’s research team and Heriot-Watt University were instrumental in helping to develop this new test.
It is important to us to help train up the industry and encourage best practice, which is why Aliaxis UK offers a suite of CPDs, including one on Active Drainage Ventilation, which delves into the reasons high-rise buildings could have issues and offers the reasoning for solutions, including how Active Drainage Ventilation attenuates any pressure immediately at the point of need.
Together, through expertise, research and experience, this industry is evolving to provide transformative solutions that make our world a safer and better place to live. CIBSE’s Guide G and new TM are a ground-breaking part of that journey as we continue to extend our knowledge and understanding.
Game-Changer for High-Rise Drainage: CIBSE TM70:2025 Explained Webinar
On February 3, Aliaxis UK will host a webinar at 11am on the new High-Rise Building Technical Memorandum and its compulsory commissioning tests. The panel discussion will give people the opportunity to ask panel members any questions they have on the topic.
Panel members will be Prof. Michael Gormley, Professor of Public Health and Environmental Engineering, and Jassim Daureeawo, CIBSE SoPHE, Technical Committee Chair, and Steve White, Technical Director Global Building Segment at Aliaxis UK.
To register for the Game-Changer for High-Rise Drainage: CIBSE TM70:2025 Explained webinar sign-up here
For more information about the new Technical Memorandum, please email technical.advice@aliaxis.com.
For more CPD information, please visit our CPD page.