Locating Underground Services Before You Dig

The cheapest insurance on your entire build costs nothing and takes a few minutes online. The most expensive mistake on the whole project can happen in the first hour of digging, before a single brick is laid, and it can kill the person holding the spade. Both involve the same question: what is buried under the ground you are about to break open?

A homeowner planning a rear extension thinks of the dig as the easy bit. Clear the patio, get a digger in, scoop out the trench. But under that patio there may be the gas service feeding the house, the electricity cable that powers it, the incoming water main, and a telecoms duct, any of which the previous owner, the original builder, or a tired groundworker put exactly where you now want to excavate. Hit the wrong one and the consequences run from an inconvenient broadband outage for the street to a fatality.

This task comes first in groundwork for a reason. You settle what is under the plot before you mark the footprint and long before you dig the trench.

The Danger, Stated Once

A buried electricity cable looks like a pipe. You cannot tell whether it is live by looking at it. Strike one with a digger bucket or a pick and the arc flash can cause severe burns, blow the tool out of your hands, and kill. A gas service that gets nicked risks an explosion and asphyxiation. A struck water main floods the trench in seconds and can wash out the bearing your foundation is supposed to sit on. Even a telecoms duct, the least dramatic of the four, takes out broadband for the street and arrives with a repair invoice you pay.

This is not best-practice advice you can weigh up. The law requires it. Under the Health and Safety at Work Act and the supporting HSE guidance HSG47, "Avoiding danger from underground services," anyone excavating has a duty to locate and avoid buried services first. CDM Regulations 2015 put the same duty on the people running the job. HSE has prosecuted and fined contractors who dug on regardless and struck live services. The duty is real, it is enforced, and on your project the builder carries it while you carry the cost.

HSG47 sets out a safe system of work in three parts: plan the work using the records you can get, locate and identify the services on the ground with detection equipment, then excavate carefully. Skip any one and the system fails. The rest of this page is those three parts in plain terms.

Stage One: The Desktop Search

Before anyone goes near the ground, find out what the asset owners have recorded. The free tool for this in Great Britain is LSBUD, LineSearch Before You Dig.

You draw your site boundary on a map at lsbud.co.uk, submit the enquiry, and within minutes the service tells you which of its 160-plus registered asset owners have apparatus in or near your search area. It then routes you to each owner to request their detailed plans. Some respond instantly with maps; others email plans within a few working days. That lead time is exactly why this belongs in your pre-construction programme, not on the morning the digger turns up.

Beyond LSBUD, the builder can request plans directly from the networks that matter on a domestic plot: the local electricity distribution network operator for cables, the gas network operator for the gas service, the water and sewerage company for mains and sewers, and Openreach for telecoms. These requests are generally free for a domestic enquiry, occasionally with a small admin fee.

Every one of these plans shows an indication, not a guarantee. HSE is blunt about it: plans give only an indication of where services run, and depths in particular drift over decades of resurfacing and re-laying. A plan tells you to expect a cable along the back boundary. It does not tell you it sits exactly 600mm down on the line drawn. That gap between the record and the reality is the whole reason for stage two.

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