What are the considerations when installing drainage solutions?

We are self building a four bed detached property, which is part of a development of four new homes in total. We are project managing our own house and a contractor is developing the other three plots. The contractor proposes to connect all four plots to one sewage pipe at the front of the development, converging at a new manhole chamber on the front of our drive. From here, it would head in a straight line to the sewage chamber located in the road.

We also need to install a soakaway at the front of our house. Are there any issues with building a soakaway close to a sewage connection? We are not sure of our finished ground levels yet and don’t know what depth the new chamber needs to be. What impact might this have on our future development potential at the front of the house, and could there be any repercussions for the other three plots?

e offer of connecting all four houses into the same run is a sensible one, as it will be the most cost-effective solution. You need to ensure a fall of between 1:40 and 1:80 on the pipework. Your developer should be able to achieve this, even if you don’t know the exact finished levels of your house yet. ey will dig and install the chamber with the correct invert (depth) to suit all four properties. e sewage system will be sealed and pipes buried in trenches lined with pea gravel, so will have no effect on any soakaways – although, clearly, they can’t be in the same place.

e variable here is the soakaways, which are used to dispose of surface water. Soakaways are usually simple pits (sometimes lined with concrete rings) filled with hardcore and covered over, eg with lawn. ese act as a repository for water from your roof, patios or driveway and rely on suitably porous surrounding material to allow rainwater to disperse. e soil around them can become saturated, so it is good practice to locate soakaways at least 5m from your foundations and 2.5m from boundaries.

ere’s no specific guidance from the Buildings Research Establishment (BRE) regarding the location of soakaways in relation to drainage systems, so it would be best to use a common-sense approach. Speak to your local building control officer to check that what is being proposed by the developer is acceptable and agree the proposed location of your soakaway before starting work. Building control are the ones who will be signing everything off, so if they’re happy, you should be, too!