The drainage codes we use today are primarily based on research that was conducted in Bern, Switzerland and the United Kingdom in the 1950s and 1960s. There is some early research that exists on tall buildings, but the buildings tested had limited discharging of appliances.

All of these studies were based on steady state conditions, meaning that they focused on the applied water flowrates to drain diameters and slope. In reality, a drainage and vent system also has air, and the time-dependent water flows within the drainage network entrain an airflow that is itself unsteady. In order to communicate changes in shear driven airflow demand, each change in water flow is accompanied by the propagation of a low amplitude air pressure transient that ensures that a modified airflow demand is recognised at the system boundary. These pressure transients are capable of depleting trap seals if they exceed +-400Pa. Flow conditions in building drainage and vent systems such as these can be defined as an unsteady multi-phase, multi component flow.

What this means is that the current codes are based on old data. The industry is still using decades-old research on limited height buildings (10 to 25 floors), with steady-state conditions, to set the standards for tall buildings 30 floors or higher. And since code and standards updates are typically managed by committees, adapting old data is often chosen as the easiest path forward.

The answer is clear: they cannot. To limit the risks of failure, engineers across the globe are forced to overdesign their drainage systems.

The good news is that preliminary research has been conducted, taking into account the unsteady state of building drainage systems for high-rises. Research institutes and manufacturers have collaborated over the last 20 years on understanding the issues specific to higher-rise buildings, and have developed solutions that meet the requirements for tall building drainage systems.

The next step is to update the codes and standards, which would benefit all stakeholders and facilitate the design of best-practice drainage systems, preventing costly and space-consuming overdesign, while ensuring peace of mind with regards to system performance.