Drainage Systems in High-rise Buildings

Drainage Systems in High-rise Buildings

High-rise buildings have become staples of urban skylines, delivering housing, office space, and commercial utility to millions. Yet behind their glass facades and panoramic views lies a critical, invisible system: the soil vent pipe drainage system. Ensuring proper wastewater management in vertical environments presents unique engineering challenges that demand advanced design, regulatory knowledge, and continual innovation.

Foul water refers to waste from toilets, urinals, and bidets. The wastewater is coming from appliances used for washing or food preparation. It flows through traps with water seals that prevent foul gases from entering indoor spaces. Wastewater is then carried via branch pipes into vertical soil stacks.

The standard foul drainage system used in UK buildings is System III, defined by BS EN 12056-2. Soil stacks are vented above the topmost branch to allow pressure equalisation and gas release. Some stacks use air inlet valves, but at least one must vent directly to the atmosphere.

For small-scale buildings, Approved Document H offers pipe sizing guidance. For high-rise or complex buildings, BS EN 12056-2 is used, applying discharge units and frequency factors based on building type (e.g., residential, hospital, or kitchen).

In high-rise buildings, with greater variability in flow, a two-pipe (secondary ventilated) system is often used. This provides a dedicated air supply via a dry stack at intermediate levels. Though effective, these systems require significant space.

To address this, proprietary solutions have emerged. Enhanced geometry fittings manage flow direction and maintain airflow. For example, flow dividers within branch fittings separate incoming flow from the main annular flow, maintaining air continuity and preventing seal loss. These designs can boost discharge capacity significantly.

At offsets and base transitions, enhanced bends maintain airflow by guiding water along the pipe walls and reducing pressure surges. These systems can eliminate the need for secondary ventilation, saving space and simplifying the services layout, critical in dense high-rise developments.

To improve flow and maintain continuous air paths, manufacturers have developed enhanced geometry fittings. These allow smoother transitions and prevent airflow disruption, increasing efficiency and reducing pressure fluctuations. For example, advanced branch fittings can boost flow capacity by over 70%, reducing the need for secondary ventilation stacks.

Despite the increasing prevalence of tall buildings in the UK, no specific drainage standards exist for high-rise buildings. As a result, innovation is driven by manufacturers offering certified proprietary systems tailored to individual buildings.

By Paulina Stanislawczyk MSc CEng MCIBSE AMSoPHE