Domestic drainage systems are covered under part H of the building regulations, and alterations to the drainage system will require Building control approval. Typically, the drains in a property constructed in the last 50 years will direct foul water into the public sewer and storm water will be directed through separate pipework into a soakaway. The foul drains are not designed to dispose of storm waters though often I find incorrect connections into the foul drains have been made over the years.
The above ground parts of the drain include the soil and vent pipe which is tall and usually affixed to the house’s flank wall. This pipe is formed in either cast iron, asbestos cement or plastic. It is designed to ventilate the drainage installation and for this reason must terminate well above any window or other opening in the wall. It should be fitted with a cowl to prevent birds nesting. The older metal pipes frequently fail where they join the underground drains. It is also quite common to find leakage where the connection from the first floor W.C. joins the main pipe.
Underground, drains should be laid at a ’self-cleansing’ velocity no less than 1;80 fall. The drain sections may be laid either in salt glazed piping, cast iron, or in more modern property, patent plastic piping. Access points for cleaning and repair (commonly known as ‘man holes but more correctly described as inspection chambers), are installed within the curtilage of the site. Very often I find the steel lids to these chambers corroded, loose or dangerously defective. In older property the inspection chamber closest to the boundary is likely to be an ’interceptor’ chamber incorporating a water trap to minimise odours from the sewer. Such chambers are fitted with a nearby fresh air inlet which projects a couple of feet above ground level.
A brief inspection of the drains very often reveals blockages which may be caused by root growth, fat build up, drain collapse or incorrect ‘fall’ during construction. My suspicions are always aroused when I see a set of drain rods left casually on display in the gardens ready to deal with the next blockage……… time to arrange a CCTV drain inspection and test!