Sources of moisture

Plumbing leaks can range from tiny drips that continue for many years and cause little damage, to dramatic mains leaks that cause large volumes of water to destroy ceilings, ruin carpets and flood basements or subfloor areas. They may cause large damp patches in wall, floor or ceiling finishes, or create pools of water. Remember that leaks may sometimes come from an adjoining property.

Leaks can sometimes be picked up by ear (e.g. when water board engineers use a listening stick), or they may be noticed via unusually high water bills, if the dwelling has a water meter. (Water meters also offer a means of finding out whether there is a mains leak: simply turn off all taps and valves in the house, and then observe, over time, whether a flow of water registers on the meter.)

Long-term leaks from embedded pipes may cause a spreading of moisture out to perimeter walling, leading to a dampness pattern that looks just like a 'textbook' case of rising damp (see The 'weeping stones' of Lough Neagh case study). Testing the suspect pipework will often confirm a plumbing leak as the cause. Leaks to pipes concealed in duct-work can create damp conditions ideal for the development of dry rot – sometimes undetected for several years until the outbreak has become very well established.

A potential source of leaks is heating pipes that run in concrete floors or screeds, and if they do leak they will probably need to be re-run. In a conventional stored hot water or central heating system the water level of the expansion tank drops so that the tank keeps refilling. In sealed central heating systems a drop in pressure on the pressure gauge of a combi-boiler pressure could be the clue.

Leaks from waste or soil systems often follow a pattern related to the use of sanitary or bathroom appliances. A common source of escapes of water from defective plumbing and/or waste pipes is from below baths and shower trays, which in the case of multi-storey flats may not reveal any specific problems in the subject dwelling, but will cause a major problem of water penetration to the ceiling of the flat below. Therefore it is good practice for the surveyor to fill up and drain sinks, basins and baths to check the efficiency of drainage and watertightness of pipework and waste fittings. Similarly, fill and flush WCs (and with due attention to health and safety requirements, a dry finger should be placed at the pan connection to detect any drips). Leaks behind WC pans may cause local wet rot to develop at boards or joists. Leaks under baths located on ground floors where the floor is of a suspended timber or suspended solid construction and where a solid ground floor is lower below the bath than the surrounding finished floor level, may go undetected for some years if the bath is panelled or tiled in and there is no easy access for inspections.

Leaks inside vertical common ducting in tower blocks can be the subject of detailed trace and access investigations, as the source of the escape of water could be much higher in the building than where the damage is manifest. These cases often involve multipole dwelling investigations and opening up of ducting to examine communal riser services; waste pipes, rainwater and water main supplies.