Evidence-based design, pressure control and public health in the vertical city
As cities continue to densify and towers grow ever taller and more complex, the engineering systems that support them are facing unprecedented demands. Nowhere is this more evident than in the drainage and ventilation systems hidden within the risers and service cores of modern high-rise buildings.
Against this backdrop, a recent Tall Buildings Magazine roundtable hosted by Geberit during Clerkenwell Design Week brought together leading engineers, drainage specialists, TM70 contributors, consultants, manufacturers and public health experts to discuss one of the most significant developments in UK drainage guidance for decades: CIBSE TM70 – Tall Building Drainage Design.
The session explored why traditional drainage guidance is no longer sufficient for contemporary tall buildings, how pressure control and ventilation strategies are reshaping public health engineering, and why TM70 may represent a decisive turning point in the evolution of high-rise drainage design.
For decades, drainage design in the UK has relied heavily on BS EN 12056 and associated discharge unit methodologies. However, while these standards remain valuable, participants agreed that they were never written with today’s super-tall, mixed-use, highly-serviced buildings in mind. Over the last couple of decades, the UK has seen multiple ‘super tall’ buildings designed and constructed with 50 storeys plus now commonplace, with some buildings such as The Shard (95 storeys) and the Pinnacle (75 storeys) creating real prominence on the London skyline.
Mike Carter of Arup explained that confidence in legacy guidance begins to diminish significantly once buildings exceed the mid-rise range. The problem is that traditional flow-based sizing methods do not adequately account for the effects of true vertical height, stack offsets, pressure transients and complex building geometries.
Professor Michael Gormley, co-author of TM70 and a leading authority on building drainage and public health engineering, described how the guidance emerged from years of research and modelling work designed to address these shortcomings. TM70 introduces a fundamentally different way of thinking about drainage systems – moving away from purely hydraulic calculations toward pressure-based system performance.
The roundtable heard that TM70 formally integrates considerations such as effective building height, treatment of offsets, pressure fluctuation modelling, advanced pressure attenuation technologies and alternative ventilation strategies. This represents a substantial shift in industry thinking.
One of the strongest themes throughout the discussion was the importance of pressure control within tall building drainage systems.
Historically, many drainage designs have focused primarily on flow capacity. However, in tall buildings, airflow and pressure behaviour can become the dominant performance issue. Trap seal depletion, transient pressures and air movement within stacks can all compromise system integrity.
Chris Grubb of Ramboll noted that many real-world tall building failures stem not from insufficient pipe sizing, but from poor pressure management and inadequate ventilation strategies. TM70 therefore provides designers with an evidence-based framework for demonstrating compliance through pressure stability rather than relying solely on historic rules of thumb.
The discussion repeatedly returned to the impact of stack offsets and horizontal transfers. In modern towers, architectural constraints increasingly introduce transfer floors, complex riser arrangements and mixed-use vertical zoning. These interruptions can create significant pressure disturbances within drainage systems if not carefully considered early in the design process.
As several participants stressed, drainage design can no longer be treated as a late-stage coordination exercise.
Stage 2 coordination is becoming critical
James Buckley of Couch Perry Wilkes highlighted the growing importance of early-stage coordination in tall building projects, particularly under the evolving Building Safety Regulator (BSR) Gateway process.
The panel agreed that drainage strategies now need to be established during Stage 2 design, while architectural and structural decisions are still fluid. Once riser positions, offsets and service routes become fixed, opportunities to optimise ventilation and pressure control diminish rapidly.
This is particularly important where advanced systems are being considered. These technologies actively manage pressure transients within drainage stacks and can reduce venting requirements, improve riser efficiency and support more compact building cores.
However, as several contributors pointed out, these systems require a higher level of engineering understanding and validation than traditional approaches.
Perhaps the most profound shift discussed during the roundtable was the reframing of drainage design as a public health issue.
Professor Gormley’s research has highlighted how pressure fluctuations within drainage systems can drive the movement of aerosolised particles and potentially create cross-contamination pathways between spaces.
This has become particularly relevant in the post-pandemic environment, where building resilience and indoor environmental quality are under greater scrutiny than ever before.
Several participants argued that TM70 effectively shifts drainage engineering away from a narrow focus on hydraulic adequacy and toward broader concepts of health resilience and pressure stability. The implications for healthcare facilities, residential towers and high-occupancy mixed-use developments could be substantial.
It was suggested that future versions of TM70 may need to include more specialised guidance for healthcare buildings and environments where pathogen control is especially critical.
The panel also discussed whether future regulations may eventually place greater emphasis on drainage system resilience as part of broader building safety and public health frameworks.
Evidence-based engineering
A defining characteristic of TM70 is its evidence-based approach.
Professor Gormley explained that the guidance is underpinned by approximately 3000 modelling scenarios alongside extensive laboratory validation and mathematical analysis.
Rather than replacing existing standards, TM70 effectively fine-tunes them for tall building applications, introducing conservative assumptions designed to improve design certainty and reduce risk.
Participants noted that this evidence-led methodology is particularly important in the context of the Building Safety Act and Gateway approval processes, where engineers are increasingly expected to demonstrate the rationale behind their design decisions.
Importantly, the panel clarified that TM70 remains guidance rather than regulation. Compliance is still governed through Building Regulations, meaning engineers can adopt alternative approaches provided they can demonstrate performance equivalence.
Nevertheless, there was broad agreement that TM70 is likely to become a de facto industry benchmark over time.
Another major theme was the relationship between drainage design and sustainability.
Martin Murray of Geberit argued that modern drainage guidance must evolve beyond simply ensuring system safety and reliability. Future standards also need to enable carbon reduction and material efficiency.
Several participants questioned whether some traditional discharge unit assumptions remain appropriate in an era of lower flush volumes and more efficient sanitary appliances. Revisiting these assumptions could potentially allow for smaller pipe sizes, reduced material use and lower embodied carbon without compromising performance.
However, the discussion also acknowledged that safety and performance must remain the overriding priorities.
There was widespread support for the idea that future editions of TM70 could incorporate stronger guidance around material optimisation, embodied carbon, circular economy principles and whole-life system performance.
Offsite construction and DfMA
The discussion also explored the growing intersection between TM70 and industrialised construction.
Tall building MEP systems are increasingly being delivered through prefabricated riser modules, bathroom pods and offsite manufactured service assemblies.
Rob Rowlands from Pipekit Offsite highlighted how prefabrication can significantly improve installation accuracy and alignment with digital design models, reducing reliance on variable site workmanship.
This aligns closely with the principles of Design for Manufacture and Assembly (DfMA), where greater precision and standardisation can improve pressure control predictability and system reliability.
The panel debated whether factory testing of prefabricated risers should eventually become standard practice, particularly for high-risk or high-rise applications. Several contributors felt that offsite assembly could play a major role in improving quality assurance and reducing installation defects in future projects.
Artificial intelligence inevitably entered the discussion, although participants were cautious about its role.
Professor Gormley warned that AI is currently unsuitable for precise engineering calculations involving drainage system performance. However, he acknowledged that AI could become valuable for data aggregation and pattern analysis once sufficiently robust datasets become available.
A recurring issue identified by the panel was the lack of operational data from real buildings. Many clients remain reluctant to permit long-term instrumentation and monitoring, limiting opportunities for performance feedback and continuous optimisation.
Several attendees argued that this needs to change if the industry is to fully embrace evidence-based drainage engineering.
Towards a global standard?
The roundtable also considered how UK guidance compares internationally. Some participants pointed to Australian standards such as AS/NZS 3500 as examples of more mature hydraulic and ventilation guidance.
There was consensus that greater international harmonisation would benefit manufacturers, designers and contractors alike, particularly as global construction supply chains continue to expand.
TM70’s authors stressed that the guidance was intentionally developed to be globally relevant while remaining compatible with UK regulatory frameworks.
The skills challenge ahead
Finally, the panel addressed the implications for the next generation of engineers.
TM70 introduces a level of systems thinking and pressure analysis that extends beyond traditional drainage design education. Participants agreed that future public health and building services engineers will require stronger understanding of airflow dynamics, pressure modelling, system validation, digital tools and integrated design coordination.
Education and CPD were repeatedly identified as critical to successful industry adoption.
As tall buildings continue to evolve, the engineering profession itself may need to evolve alongside them.
Top 10 key takeaways from the TM70 roundtable
- TM70 fills a critical gap in UK guidance
Traditional standards such as BS EN 12056 were never designed for today’s super-tall, complex buildings. - Pressure control is now central to tall building drainage design
System performance is increasingly governed by airflow and pressure behaviour rather than flow alone. - Drainage engineering is a public health issue
Pressure transients and aerosol movement may have implications for pathogen transmission and health resilience. - Height fundamentally changes drainage behaviour
Effective stack height and offsets must now be considered as core design parameters. - Early-stage coordination is essential
Drainage and ventilation strategies need to be resolved during Stage 2 design, not left until later coordination. - TM70 is accelerating evidence-based engineering
Designers are increasingly expected to justify system performance through modelling and validation. - Pressure control technologies are reshaping riser design
Advanced systems are enabling more efficient and compact tall building layouts. - Offsite manufacturing supports better drainage performance
Prefabricated risers and modular MEP systems can improve accuracy, consistency and verification. - Future guidance must address carbon and material efficiency
Drainage standards are likely to evolve toward whole-life performance and embodied carbon reduction. - The industry skills base must evolve rapidly
Engineers will require stronger expertise in pressure modelling, digital coordination and integrated system design.
The Tall Buildings Magazine roundtable made one thing abundantly clear: TM70 is far more than a technical memorandum. It represents a broader shift toward evidence-based, performance-led and health-conscious drainage engineering for the vertical city.
Attendee List
- Facilitator Darren Richards, Managing Director, Cogent Consulting
- Martin Murray, Specification Manager, Geberit
- Rob Rowlands, Commercial Director, Pipekit
- Chris Grubb, Associate Director, Ramboll
- Mike Carter, Director and Chair of SoPHE, Arup
- James Buckley, Director & Chair of SoPHE Midlands, Couch Perry Wilkes
- Professor Michael Gormley, Professor of Public Health and Environmental Engineering, Heriot-Watt University
- Adam James, Specification Manager, Geberit
