Why plans are so often missing or wrong
Original as built drawings for pre war housing rarely survive, and where they do they show the drainage as designed rather than as installed. Later work compounds the problem. A rear extension in the nineteen eighties may have diverted a run, a new bathroom may have been connected into the nearest available pipe, and a driveway may have been laid straight over a chamber.
The result is that the only reliable plan is one produced from what is in the ground now. That is what tracing gives you.
How tracing actually works
A small transmitting sonde is fitted to the camera head and pushed along the pipe. Above ground, a receiver picks up the signal and locates the head precisely, both in plan position and in depth. The engineer marks the ground as the camera moves, and the result is a physical line of marks following the pipe, with depths noted at intervals.
That is combined with a chamber survey, where every accessible cover is lifted, the connections in and out are recorded, and cover and invert levels are taken. Between the two you get a plan that shows the route, the direction of flow, the depth and where each branch joins.
What the finished drawing shows
- The route of each foul and surface water run across the site.
- Chamber positions with cover and invert levels.
- Pipe depths at intervals along each run.
- Direction of flow and the point of connection to the public sewer.
- Which connections are foul, which are surface water and any misconnections found.
- Redundant or abandoned runs, which are surprisingly common.
When you genuinely need one
Before any extension, garage, conservatory or substantial hard landscaping. Building over or close to a drain is not automatically prohibited, but it needs to be designed for, and the design cannot be done without knowing where the pipe is and how deep it runs. Discovering a live sewer once the foundation trench is open is expensive and delays everything.
Also worth doing before buying a property with unclear boundaries or shared drainage, before installing a driveway with a soakaway, and where a property has repeat blockages that never seem to have a source, because a forgotten redundant run or a misconnection is often the reason.
Building over or near a drain
Where a proposed structure sits over or beside a drain, the usual outcomes are to divert the run, to encase or bridge it with a lintel arrangement designed by the engineer, or to relocate a chamber. All three are ordinary pieces of work when they are planned. All three are difficult and costly when they are discovered halfway through a build.
Where the pipe is a public sewer rather than a private drain, a build over agreement with Scottish Water may be required, and the plan produced by the trace is the document that conversation starts from.
Combining tracing with a condition survey
Because the tracing is done with the same camera that inspects the pipe, it makes sense to do both at once. You get the route and depth for the build, and the condition of the run for your own information, from a single visit. If a defect shows up in a section that is about to be built over, that is the moment to repair it rather than after the slab is down.
We survey and trace across West Lothian, Edinburgh, Falkirk, Lanarkshire and Fife, and we provide the drawing in a form architects and building warrant applications can use.
What it costs and how long it takes
A trace and chamber survey on a typical domestic property takes a couple of hours on site, and the drawing follows within a day or two. It is priced as a fixed fee once we know the size of the plot and how many chambers are involved, so there is no open ended charge.
Set against the cost of redesigning a foundation mid build, or of a build over agreement being refused because nobody can say where the sewer runs, it is one of the cheaper pieces of survey work in a construction project. Architects and building standards officers both prefer to see it early rather than at warrant stage.
Questions we get asked
How accurate is drain tracing?
Position is typically accurate to within a few centimetres and depth to within about ten per cent, which is more than adequate for design and excavation.
Can you trace a pipe with no access chamber?
Usually yes, by launching from a gully, a rodding eye or a lifted toilet pan, though access affects how much of the run can be covered.
Do I need a plan for building warrant?
Where drainage is affected, the authority will want to know what exists and what you propose, and a traced plan is the simplest way to show it.
Will you find a septic tank or old soakaway?
Often yes. Redundant tanks and soakaways show up as terminations that do not connect to the sewer, and they matter for both building and safety.