Water under the Floor…

More and more these days I seem to be dealing with problems of water beneath suspended timber floors, sometimes it’s quite deep enough to paddle in!  Once people are aware that it’s there, they’re quite terrified of it and want to know how to get rid of it.  Well, often the answer is: ‘You can’t’. 

Unless its caused by a substantial leak, from a water main or a cracked drainpipe for example, the most common source for this type of water is the ‘water table’, which can be thought of as the ambient level of water in the earth,  Although in most cases it isn’t actually the ambient level, it’s more likely to result from a ‘perched’ water table, which occurs when a house is built on a non-permeable material such as clay.

Over the past few years (this article is published in 2008) the summer seasons in the UK have been much wetter than normal, and the heavier rainfall we usually associate with the winter months hasn’t had chance to drain away before the summer rainfall has replenished it.  Consequently, the water table in some places is higher than its long-term norm.

As I alluded to earlier, it isn’t really practical to consider draining or pumping this water away; it’ll be replenished as fast as you’re pumping.  You could create a tank around the perimeter walls inside the sub-floor areas of your house, but this would be buttock-clenchingly expensive and require a significant amount of disruption.

Another thing you could try is raising the level of the solum (the earth beneath the floor) so that it’s above the highest level of the water table; this could be achieved by tipping gravel or some other form of hard-core.  The water table wouldn’t have gone away but at least you wouldn’t be able to see the water.  If you made a neat job of it, levelled it off and then laid a heavy-duty Visqueen sheet on top, it would also help to reduce the relative humidity beneath the floor.

However, as this is a natural phenomenon and it’s probably affected your house for a long time - probably since it was built - the simplest thing to do is to just accept it and make sure that you have excellent ventilation beneath the floor.

This means plenty of efficient airbricks: not the half-blocked with grunge and years of dirt terracotta or masonry ones that are associated with many properties.  Modern ones, made of either plastic or aluminium, provide much better ventilation than the older types and are well worth considering if you’re at all worried about the health of your floor joists (don’t even think about it if you live in a listed building). 

If you’re at all concerned you have a sewage leak, get the local Water Authority to test the water for contaminants.  The water table is usually pretty clear and doesn’t often smell (although some would dispute this).

‘Course, the really adventurous install lights and breed goldfish, but that’s another story.