Where do cables run in walls in the UK?
In set zones. The IET, which publishes the UK wiring regulations, sets out where a cable buried less than 50mm into a wall may run without mechanical protection. It can run straight up, down or across to a socket, switch or light point. It can also run within 150mm of the top of the wall, or within 150mm of a corner. Electrical Safety First gives the same advice to people doing DIY: buried cables should run horizontally or vertically from sockets and switches.
The zones carry through thin walls. If a wall is 100mm thick or less, a socket on one side creates a zone on the other side too. So check both sides before drilling an inside wall.
The zones tell you where cables are likely to be. They don't make the rest of the wall safe. Cables can run outside the zones if they have other kinds of protection, such as an earthed metal covering or metal conduit. Cables buried less than 50mm deep without that protection should also be protected by an RCD, a safety switch in the consumer unit. That cuts the risk of a shock, but it doesn't stop you drilling through a cable.
A trick we used a rough sketch of each wall before drilling. We marked the sockets, switches and light points, shaded the zones in pencil, and only drilled outside them.
Where are pipes in walls?
Assume they could be behind any wall. The NHQB warns that pipes and electrical cables may be hidden behind walls, and says to use a cable and pipe detector before drilling or fixing anything.
Stud walls (plasterboard on a frame) are hollow, and services can pass through them. Knauf's installer manual for its plasterboard walls includes details for pipes running through them. Where a wall is built on metal studs, the RCD rule applies to cables inside it at any depth.
Floors and lofts hide services too. The NHQB says loft spaces may contain pipework, electrical cables or ventilation, and to take care not to damage them. NHBC's standards for builders also expect any services under a wood floor finish to be tested before the floor goes down.
How can I tell if water pipes are behind a wall?
Use a cable and pipe detector, as the NHQB suggests. Electrical Safety First says a good-quality detector can help track buried cables before you start work.
It also says to shut off the power for DIY close to electrics. If you hit a water pipe, turn the water off at the stop tap.
Underfloor heating pipes
Underfloor heating pipes are hidden in the floor. NHBC Foundation guidance for builders says this makes them potentially vulnerable to puncture from later work that involves screwing or drilling into the floor. It says the installer must clearly and accurately communicate the layout. Its example is pipe loops running under a toilet, where fixing screws too close to the loops could cause a leak.
Ask the builder for the layout before you fix anything to the floor: a door stop, a new toilet or a fitted wardrobe. The heating page covers how to run it.
Can I get drawings of what's behind the walls?
Ask, but don't expect a full map. Three documents come close.
- The health and safety file. The builder must give you one at completion. HSE guidance says it should consider including where significant services run, and as-built drawings.
- The heating and ventilation instructions should show where each system is, on a floor plan.
- You should get the builder's photos of the build quality. They show insulation, not cables.
The builder doesn't have to let you visit during the build. If it does, it must tell you what safety precautions to take.
The stop tap and the outside stop valve
Thames Water says the inside stop valve, also called the stopcock or stop tap, is usually just after the water pipe comes into the house. Common places are under the kitchen sink, in an airing cupboard, under the stairs or in the garage. It suggests checking every month that it still works.
The outside stop valve is usually under a cover on the path or the road, sometimes near the water meter. Thames Water says to use it only in an emergency, and you may need a special key to turn it.
Gas and electricity meters
Know how to turn off the gas. Cadent says the shut-off handle is usually near the gas meter and turns 90 degrees. If you or your builders hit a gas pipe, National Gas says to call the National Gas Emergency Service on 0800 111 999, day or night.
Not everything in the electricity meter box is yours. GTC, a network operator, explains that it is responsible for the incoming service cable and the cut-out (the box that cable runs into). The meter belongs to your energy supplier, and only your supplier can remove the main fuse.
The official checklist expects meter boxes outside to be securely fixed, level and clean, with the pipework sealed where it goes in. If they're not, add it to your snag list and report it to the builder.
What you own, and what the water company or network owns
Water. Ofwat says the water company looks after the mains and the pipe up to your property boundary. From there, the supply pipe into your home is usually yours, along with any stop taps on it. Thames Water adds that all your internal pipes, appliances and fittings are yours. There can be exceptions, so Ofwat suggests checking with your water company and your deeds.
Gas. Cadent, one of the gas networks, looks after the pipes in the street and up to your meter. Your supplier is responsible for the meter. The pipes from the meter to your boiler and cooker are yours.
Electricity. GTC says the network operator is responsible for the service cable and cut-out, and the supplier owns the meter. The consumer unit is part of your own wiring, to be looked after by a qualified electrician.
Will drilling affect my warranty?
It can. Premier Guarantee says damage caused by DIY or maintenance is unlikely to be covered by its policy. It also warns that building over water or gas pipes, or electricity or telephone cables, could damage them. Pipes and cables on your side of the boundary or meter are yours to repair, as above.