The Self Build Self Help Site Drains
Sub header photo of a roof

Laying the drains is something that can be achieved by the self builder. You will need a small digger which you can hire from the many hire companies around, and there are plenty of small companies (often one man companies) that will hire a digger and driver for less than the hire charge for a digger from a hire point. If you take this option, it is likely that the contractor may have experience of laying drains and may be prepared to help as well as excavating and back filling.

Work out what materials you need in advance, but be prepared in that the layout may vary from expectations once the trenches are dug and you determine how everything will actually fit together. The position of 4" soil and ventilation pipes, rainwater down pipes and 4" underground pipes may be shown on architects plans - but make sure that these are sited taking into account the actual positions of sanitary ware - where you may site them in different positions to those shown by the architect.

A very good brochure (PDF) describing various drain components is the Huntley Plastics Ltd Guide to Drain and Sewer Systems or their web site.

Internal or external soil pipes?

There are 2 options for 4" soil pipes - internal and external. In the main this is a matter of choice, the criteria being:
  1. do you want the pipes to show externally? (white pipes look better and should cost no more than grey)
  2. will the rooms be able to accomodate boxed-in pipes easily - can they be accomodated in corners?
  3. internally they will vent via slate vents in the roof, or can be vented into the soffits
If you prefer the clean lines externaly, your architect will have a good chance of desiging for internal pipes.

Get the drains done sooner rather than later

Get the drains done before the scaffolding is erected. The ground can then be levelled nicely for the scaffolding. Once the scaffolding is down much of the heavy work will have been completed and you will be more into fitting out and finishing - if you leave it, excavating, laying drains and backfilling will seem more like a chore at that stage.