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Build Advice

Installing Drainage

The decision on whether to construct your drains once you have reached oversite or damp proof course (DPC) level with the underbuilding is a tricky one. It may seem best to get drains out of the way and backfilled at the same time as all of the other groundworks are taking place. On the other hand, if work on the superstructure is to continue, they may be in the way, prevent the erection of scaffolding or get damaged by the ensuing works.

There are two main functions of your Drainage: The first is to dispose of 'foul water' the domestic waste from bathrooms, toilets and sinks etc. The second is to deal with 'surface water,' the rainfall from the roof etc.

Septic tank installation on a plot of land for a self build homebuilding project 1050241541

Foul Drainage
Foul drainage is best disposed of to the ‘mains drains', which may be adopted or private at the point of connection. If mains drainage is available, you will be required to connect, even if this is not the cheapest option. If a sewer is not available, there are at least three other options:

  • On site septic tank: This passes partially treated effluent into subsoil irrigation.
  • Treatment plant: This passes more refined semi-sterile effluent into subsoil irrigation, a soakaway or a watercourse.
  • Cesspool: This is where the household effluent is stored for collection and off site disposal.

Surface water is usually dealt with by taking it to soakaways constructed 5 metres from the home. These are often simple holes filled with rubble but in areas of poor drainage may have to be more complicated brick or concrete chambers. If a watercourse is available, this is the best option. Consider recycling your rainwater, not only is it ecologically friendly but with our partner's tank and assembly kit, it offers a simple alternative.

Surface Water
Most self builders opt for plastic type drainage, which is easier to handle on site and stand to test. Drains must be laid in carefully dug trenches and surrounded by clean pea gravel. All routes must follow straight lines and all changes of direction must be made at a manhole or inspection chamber. Falls are usually 1-40 but can go as low as 1-100 if plastic drainage is used. No drains can be backfilled before inspection and testing.