Damp management and remediation

In the short-term it is difficult to prevent damage to properties that are subjected to disastrous flood water. But much could be done to prevent internal flooding that is caused by poor design, failing materials or components, or sometimes just carelessness on the part of building occupiers.

Overflows are provided at construction stage for tanks in lofts, WC cisterns, baths, basins and sinks. The pipework is often routed out of the building to project from the face of the wall as a 'warning pipe' so that discharge water or sometimes waste effluent (from a bath) emerges from the building in a position to alert the occupant to the potential problem.

Unfortunately, many overflow pipes from sinks, baths and basins are not of sufficient diameter to cope with the potential volume of water that could be produced from the hot and cold taps. Much damage must be caused every year by this design shortfall. Additionally, overflow pipework is often of an inferior standard - sometimes relying on poor quality 'push-fit' pipe connections, assembled behind sinks, under baths or in roof voids where it is difficult for the plumber to reach. Once a bath, sink or basin has over-flowed, the flood water usually travels downwards to soak through ceiling finishes below, and may even track down through the property via ducts and pipe holes to cause damage many floors below its source.

These problems could be avoided with a little forethought at the design stage.

• Bathroom floors in housing blocks could be designed as watertight trays to contain overspill from baths, showers or basins, incorporating kerbed protection to vertical pipe ducts and a slightly raised door threshold.
• The overflow pipes that are so often ignored for months (even years) could be fitted with electronic or mechanical alarms to alert occupiers and buildings managers to the fault.
• In some basements that have been fully water proofed with a drained cavity membrane system they have been fitted with sumps and dual pumps with an alarm and battery back-up that can serve as fail safe mechanisms.
• Modern cisterns now incorporate integral overflows.