Studying the drainage plans for your new build might not seem like the most exciting aspect of the drawings. However, drainage can be an expensive part of a build and its important to consider the cost implications of what is going in below ground!
The lower ground floor of the house at Gamekeeper's will sit nestled in the sloping hillside meaning that excavations to 3m deep are required for the foundations. However, the garage will be built at ground level so its foundations are just half a metre down.
Both the garage and the house have a perforated land drain around the back perimeter to take storm water run off away from the waterproofed concrete retaining walls and around the buildings to discharge into the large pond at the front of the house. This second defence against water breaching the property is key to any new basement design.
The storm drainage pipes for the main house and the garage are link up under the driveway between the two buildings before the run off is taken down to the pond.
Result: The garage drainage runs had to be dug down to be at a similar level as the house drainage. A deep labyrinth of pipes now run below the new driveway and when building control came to sign off it became clear that they require a concrete access point (once you go deeper than 2.5m) for future servicing and maintenance checks as once you are down this deep it has to be wide enough for a person to enter. So the black plastic drain shown above had to be removed and replaced with....
A very large concrete entrance chamber complete with a nice yellow step ladder down....
Cost overrun of £1.5k per concrete drain and the drawings indicate we need three of these!
Conclusion: This probably would have been a difficult problem to avoid given the garage and house are being built at 3m difference in ground levels but separating the two drainage runs for the buildings entirely might have been a lot cheaper then digging such deep trenches and then having to replace the normal drain service pipe with the concrete drain. It's sometimes difficult to see these problems early on even if I had reviewed the plans in more detail I personally wouldn't have spotted the building regs requirement for the concrete drain but the cost implications were painful at such an early stage of the build.
"Experience is simply the name we give our mistakes"