SPONSOR CPD PROGRAMME Continuing professional development (CPD) is the regular maintenance, improvement and broadening of your knowledge and skills, to maintain professional competence. It is a requirement of CIBSE and other professional bodies. This Journal CPD programme can be used to meet your CPD requirements. Study the module and answer the questions on the final page. Each successfully completed module is equivalent to 1.5 hours of CPD. Modules are also available at www.cibsejournal.com/cpd Ensuring effective foul water drainage in high-rise buildings This article provides an overview of foul water drainage systems in high-rise UK buildings and considers how enhanced geometry fittings can improve performance and reduce space requirements As described by the approved document (AD) part H of the England Building Regulations, the prime purpose1 of a sanitary drainage system in a building is to convey foul water to an external sewer (or appropriate alternative). Sanitary drainage systems should minimise the risk of blockage and leakage, and be accessible to clear any blockages. The installation must prevent foul air from the drainage system from entering the building, and be ventilated so that any foul gases can be released to atmosphere without adversely affecting building occupants. Surface water drainage carrying rainwater (and melted snow and ice) from gutters and rainwater pipes is collected separately and recycled or, where available, passed into specific surface water sewers. This is discussed extensively in CIBSE Guide G, Public health and plumbing engineering.2 For sizing and determining appropriate piping arrangements for soil (named after the euphemism night soil) and waste pipes which are collectively known as foul water drainage UK installations should conform with BS EN 12056-2:2000 Gravity drainage systems inside buildings. This is referenced by the Building Regulations (for example, as described in AD part H of the England Building Regulations) and other standards appropriate to the particular building application and location. Section 3 of CIBSE Guide G2 draws the information from a number of sources and provides agood reference when developing designs for building water drainage. Products usedin drainage systems should conform to the EU Construction Product Regulation and national requirements for example, in England this is defined in AD7 Materials and workmanship.3 Foul water is generally defined as waste from a WC or urinal, bidet or appliance used for washing receptacles for foul waste, or water that has been used for food preparation, cooking or washing. When water flows away or is flushed from a fixture, it will first pass through a trap that employs a water seal (normally a water trap) to prevent gases from drains and sewers from entering the occupied space. The soil and waste pipes also known as sanitary pipes carry water discharged through the branch pipework into the main vertical soil pipe, or stack. The diameter of the branch pipe is determined not only by the fixtures that drain into it, but also by the distance that it runs before joining the main stack. The foul drainage system typically applied in UK buildings is what is known in terms of BS EN 12056-2 as System III. Under working conditions, traps should retain a minimum seal of 25mm of water and, as specified in the national annex to BS EN 12056-2, for UK class III installations, comprise a static trap water seal of 50mm or 75mm, depending on the particular fixture. The soil stack is continued upwards above the topmost branch (now solely a stack vent) and this combined soil and vent pipe may provide an outlet to vent foul gasses, as well asbeing a source of vent air to relieve pressureimbalances. Stack vents may be terminated by an automatic, one-way air inlet valve, but at least one stack vent in the buildings system must allow relief of foul gas to atmosphere. For single domestic applications, small commercial premises and some smaller groups of homes, the guidance in AD part H directly provides the design data to determine www.cibsejournal.com August 2019 49 CIBSE Aug19 pp49-52 CPD v5.indd 49 19/07/2019 15:05