Minimum distance between foundations and drains/services?

[MattD]

We are due to begin put drains and services in for a project soon but are yet to finalise the foundation details with the structural engineer. The services will be running alongside the outside of the buildings. One building will have spot foundations, and the other strip founations. Since we don't yet know how deep our foundations will be, I can't say for sure whether the drains/service trenches will be higher or lower than the bottom of the foundations.

 

What is a minimum distance from foundations for service trenches to run where the foundation depth is not yet known? I'd rather put them a bit further away from the buildings to avoid future problems, but we're on a slope and putting them too far from the building would also lead to excessive groundworks so am looking for a sensible but safe distance.

 

Of course the inspection chambers will come a little closer than the drains themselves, so there may be different distances for (1) drains, (2) inspections chambers and (3) other services (water pipes, cable ducts etc). I'm assuming that there is no minimum distance for (3), but their inspection chambers may need to be a certain distance?

Edited January 22 by MattD

[Conor]

I really wouldn't bother putting in services until after the foundations are done. Maybe the main connection runs to sewer / soakaway etc, but nothing near the building. Chances of something being on the wrong place are too high, as well digger smashing something.

[MattD]

Thanks @Conor. Actually that sounds very sensible!

[saveasteading]

The principle is to not have the drains take any load from the building. In approx terms the loads spread at 45° into the earth from the bottom of the foundation. so keep drains above that notional line.

But there's a very strong chance of damaging the drain if in early. So work out where it's going but do it later.

 

If there isn't room then ask again.

 

[George]

In theory they can be as close as you want... But what changes is the manner in which they are built, both in the temporary and permanent condition.

 

Check out diagram 8 in part H of the building regulations for concrete backfill to avoid long term undermining.

 

For temporary stability you may need to do short runs or provide excavation shoring if the foundations are undermined.

 

Above foundation formation level there is unlikely to be issues.