Drainage is another large part of carrying out groundworks, with appropriate provisions having to be put into place for the correct disposal of waste and rainwater. In areas with high water tables or poor natural soil drainage, special systems may have to be installed around the perimeter of a building to prevent the foundations from becoming waterlogged. Here we shall look at the common types of drainage systems and how they are installed.   

Soakaways

Soakaways are the primary source of rainwater disposal used within modern residential construction. At its most basic, a soakaway is a hole in the ground that is filled with well-draining materials such as hardcore or rubble. Rainwater collected by the gutters of the building is piped into the hole to allow for the water to slowly drain into the deeper layers of the soil, away from the foundations of the property. In the past, these soakaways would have been lined with honeycomb masonry to promote proper draining. In modern times, plastic soakaway crates are very common - these are hollow mesh crates that are buried in the ground to promote water drainage. If the ground surrounding the soakaway has a very high water content, the soakaway allows a space for excess water to collect without saturating the surface of the garden or surrounding land. Unless otherwise impractical, soakaways are always installed as a means of disposing of waste rainwater. The alternative is to dispose of the water into the main waste drain - a scenario that prevents the water from re-entering the earth as nature intended. Soakaway pits are dug 5m away from the property that it is servicing, and 2.5m from any surrounding boundaries. Exceptions can be made in some scenarios depending on the geography of the surrounding area.  

Foul wastewater drainage

The “foul” is the main waste disposal drainage that services a property. Bathroom and kitchen sink waste are connected to the foul - which is typically a 4” plastic or clay pipe that runs off of the property under the ground and into the main street sewer. Under the streets are a series of wider drainage and sewage tunnels, with all of the waste pipes from the properties on that street running into it. During the creation of new plots or estates, new foul pipes must be connected into the street to service the property. When carrying out renovation and extension works, new bathroom and kitchen sinks can be plumbed into existing foul pipes. Alternatively, existing foul pipes can be tapped into and extended further into a property to accommodate new services. Where possible, rainwater is discouraged from being disposed of into the foul. The drainage must have a fall on it from the highest point until it reaches the road. A fall of around 1:40 is typical for residential waste. If the pipe features not enough fall, then larger items that are flushed may become lodged. Alternatively, if the fall is too great, then the same issue can occur, with the water draining too fast to carry heavier items with it. 

Rodding access and inspection chambers

At multiple points throughout the run of a foul, inspection chambers and rodding access points must be made available. These concrete or plastic chambers feature removable lids that allow access to the inside of the run of a foul in the event of a blockage or leak.

French drains

French drains are a form of soakaway that are installed around the perimeter of properties in areas with a high water table. A trench is dug and filled with well-draining material such as gravel or hardcore. This trench allows for excess water to appropriately drain away from the external masonry and foundations of a property. 

Aco drains

This is a modern type of drainage that often comes in the form of precast plastic lengths. The lengths are installed in the ground at surface level, at the point where flat surfaces such as driveways, patios, and steps meet the vertical walls of the property. The grooves in the surface of the drain allow water to pass into the trough and be directed away from the building and into the foul or soakaway. These can commonly be seen before garage doors, on plots where the driveway slopes towards the property. In times of heavy rain, the water can deluge down the driveways and under the garage door. Appropriate aco drainage can help to remove this excess water.