Regulations state that vent pipes that are situated within 3m of an opening window must terminate at least 900mm above the eaves. On a two-storey building that generally means that the open end of the pipe will be above the level of the eaves. One way to avoid such a high-level installation is to use an External Air Admittance Valve at the top of the pipe, which allows air to be drawn in to balance any negative pressure but does not let out any foul gases - it is essentially a one-way valve.

Remember, the vent size is not based on the trap or fixture drain (trap arm), but the drain size that continues downstream from the point where the vent and fixture drain connect. The drain size is determined by the fixture unit load in accordance with Tables 709.1, 709.2, 710.1(1), and 710.1(2) in the IPC. Hence, if the drain size is 4 inches (102 mm), a 2-inch (51 mm) vent is required. A 3-inch (76 mm) drain would require a 1½-inch (38 mm) vent. A 2-inch (51 mm), 1½-inch or 1¼-inch (38 or 31.8 mm) drain would require a minimum 1¼-inch (31.8 mm) vent, this being the minimum size allowed. A waste system, as previously mentioned, is made up of pipes and fittings designed to carry wastewater from sinks, showers, bathtubs, washing machines, and dishwashers out to the sewer. Because these pipes shouldn't have to carry any solid waste away (stop scraping leftover food down the kitchen sink!), they don't need to be as large a diameter as the soil system pipes, meaning that less space is required to install them. The most common waste pipe sizes in the UK are 32mm (suitable for low volume outlets, such as small hand basins), 40mm (suitable for most kitchen sinks, showers, and baths), and 50mm (suitable for more commercial applications, or for connecting multiple waste pipes into a single flow.

Venting a Bathroom Fan into the Soil Stack.

Every building that has drainage pipe systems: toilets, sinks, and baths, are connected to a series of interconnected pipes. Together, they all connect to a network of horizontal pipes called waste pipes, or soil and vent pipes. These horizontal pipes transport any wastewater from a property by joining with a vertical pipe outside of the building. Note: If your property uses a sewage treatment plant, septic tank, or cesspool instead of a connection to the mains drains, there must be AT LEAST one open vent in the system to prevent a dangerous build-up of gasses. Solving pressure build-up with an Air Admittance Valve By legislation, ventilation pipes must be able to handle an air test of 38mm of pressure on a water gauge for three minutes. A 25mm water seal should be maintained. It is important to always test pipes after an installation because if there is not the right balance in pressure, it could even lead to burst pipes. Along with this, in the winter months an inconsistency in pressure may lead to things such as dried up taps as well as various other problems. So to ensure your whole system runs as it should make sure to correctly carry out the drain testing procedure. For more information on testing pipework properly you can see our ‘All about drain testing’.

Tees - used to connect two waste pipes (single Tee) or three waste pipes (Cross Tee) together at a 92.5-degree angle. Conversion Bends - used to create changes in direction while also converting the connection type between push-fit and solvent weld. In some situations pipe from your ground floor closet can directly get rid of water when the depth from the floor to the drain has an invert of 1.3 meters. This is the maximum invert allowed without breaking the rules and regulation put in place by the government. The diagram shows this in further detail.In recently constructed homes, there may be a single horizontal soil vent pipe that terminates below ground level as well as a clean-out cap on top of the pipe. While this is not strictly part of the three-pipe method, it is designed to operate in a similar fashion and can work just as well provided you have outdoor access to the clean-out cap so it can be used for cleaning during non-building seasons or if needed. The only thing I can think of is to cover the hole with some fibreglass insulation which would hopefully keep the heat in, but could make the fibreglass damp and cause other problems, so I have left it open for now.