If you need any help with any type of French Drain, timber repair, maintenance or other damp problems Property Repair Systems will be pleased to give you completely free, no obligation advice on 01626 336180. The information you need may be in the project below, if not, call them.
A French drain is simply a small trench, dug to a gradient that will allow surface water, or the top of the ground, to drain away from a building or area that is prone to surface water build up and/or flooding. The usual reason for constructing a French drain is to relieve a build up of water against a house wall. In older properties this may manifest itself in the form of rising damp and decaying brickwork and mortar joints. A French drain may not solve the problem totally and other means of controlling the water may need to be found. E.g. Insertion of a damp proof course. All other surface water drainage should be checked also before constructing a French drain, this includes rainwater pipes and gullies.
Rainwater should never be discharged into a cesspool or septic tank and foul drainage should never be discharged into a French drain or soakaway.
A French drain is not intended to replace existing surface water drains, and its life may be temporary because of a tendency for the shingle and stone to get clogged up with earth. It is advisable to use a French drain with a perforated land drain in the bottom, which may be wrapped in weed fabric from a garden centre, diy store or builders merchants. A layer of this fabric may be inserted into and across the trench to ensure longer life by stopping the fines from the earth clogging the stone. It must be indicated that there can be a danger of a French drain functioning rather too well and drying out the earth surrounding the house completely, which may lead to settlement of the foundations.
A French drain should be no deeper than the foundations of a building and in the case of older buildings, the side of the trench should slope away from the building at no less than 45 degrees. This is to maintain the lateral support of the foundations by the ground surrounding them. The surface of the drain may be covered with top soil to match the surrounding areas, but a layer of weed fabric is recommended for the above reasons.
The water, once entering the trench will have to run to a suitable drain off point, and in most cases this is a soakaway or watercourse. If a wall has been soaked continually by water against the building a French drain will also allow it to evaporate from the wall in the drier periods. The French drain, if a drain pipe is included, should be regularly maintained as a surface water drain should be. Regular rodding eyes should be included in the "run" and a small access chamber should be included where there is a change of direction. If the foundations of the building are very shallow then the French drain should be constructed at a minimum of 1 meter away from the building.
If you have any problems with new, or existing French Drains or soakaways, contact Property Repair Systems.
A soakaway is simply a hole in the ground filled with rubble and coarse stone with a drainage pipe laid to it removing surface (rain) water from other areas. The soil in which the soakaway is placed must be granular with good drainage properties. It is pointless sinking a soakaway in clay.
Soakaways must be at least 5 metres from any habitable building by most local authority regulations. The pipe flowing to them should be of at least 75mm diameter which is the minimum pipe size for any surface water drainage. 100mm is the recommended size. This pipe should be laid to a fall of 1 in 40. The size of the soakaway should be a minimum of 1m x 1m x 1m below the bottom of the incoming pipe. The stone infill should surround the pipe and finish approximately 100mm above it. An impervious layer should then be placed on the stone such as thick polythene, tarpaulin, or even a bed of concrete (A1). Topsoil can then be placed on top of this layer to restore the garden level (A).