External Meter Box: Gas vs Electric, Surface vs Recessed, and How It's Built In

A rear extension swallows the outside wall the gas meter is bolted to, so the meter has to move. The builder builds a box into the new blockwork and the wall goes up looking neat. Then the homeowner discovers the energy supplier can't move the actual meter for nine weeks, the scaffold is already up so the gas network won't attend, and the box is the wrong size anyway. The box is a cheap part. Getting the right one in the right place at the right time, and booking the meter move early, is the bit that goes wrong.

What it is and what it's for

An external meter box is the weatherproof enclosure on an outside wall that houses a gas or electricity meter. It protects the meter from rain, frost, and knocks, keeps the supply head and meter tidy, and lets the meter reader and the network engineer reach the meter from outside without anyone needing to be home. The box has a lockable door, opened with a standard triangular meter key, so utility staff get in but the meter stays secure.

On most extensions the box is being fitted because a meter has to move. The new wall covers the old meter position, or the new footprint sits over the supply run, and the meter and its box have to relocate to a wall the network can still reach. A meter sealed inside your new kitchen is not allowed: gas and electricity meters have to stay on an external wall so the network can read, inspect, and isolate them. So the builder builds a fresh box into the new external wall during blockwork, and later the supplier moves the meter into it.

The box is a standard, off-the-shelf component, not a bespoke item. It comes in recognised sizes matched to UK domestic gas and electricity meters, with a back plate (the panel the meter and supply head fix to) and a base that lets the supply duct enter from below. The builder fits the empty box. The meter that goes inside it is moved and connected by the energy supplier and the gas or electricity network, never by the builder and never by you. That split is the single most important thing to understand about meter boxes, and the part that catches people out.

The two box families: gas and electric

Gas and electricity meters live in different boxes. They are not interchangeable, and you cannot put a gas meter in an electric box or the reverse.

A gas meter box houses the gas meter, the emergency control valve, and the regulator. The standard UK domestic gas box is a recognised size designed around a standard credit or smart gas meter, so a box described as "UK standard" or "Mark 2" fits the meter your network will install. The defining feature of a gas box is that it must vent. Gas is lighter than air for natural gas, so a small leak inside the box needs somewhere to escape rather than pooling. Gas boxes are moulded with vents top and bottom and a base that drains, and they must never be sealed airtight.

An electric meter box (also called an electricity meter housing) holds the electricity meter, the service head or cut-out (the sealed unit with the supplier's main fuse), and the meter tails feeding your consumer unit. It does not need to vent for safety the way a gas box does, but it still has a base entry for the service cable and weep points so condensation can drain. Electric boxes come in single-phase domestic sizes and larger three-phase sizes for higher-demand supplies.

Both families are usually moulded from GRP (glass-reinforced plastic, a tough weatherproof composite) or a similar UV-stable plastic, with a lock and steel or stainless hinges. The standard colour is white, with cream and brown offered to suit render or brickwork. The door colour is cosmetic; what matters structurally is the box size, the box type, and the back plate matching what the network needs to bolt the meter to.

Surface-mounted, recessed, and semi-recessed

The other choice is how the box sits in the wall. There are three forms, and the right one depends on the wall build-up and how much the box can project.

A surface-mounted box bolts onto the face of the finished wall and stands proud of it. It is the simplest to fit, needs no recess formed in the masonry, and suits a solid wall or any situation where you do not want to interrupt the blockwork. The trade-off is that it sticks out, which can look bulky on a narrow side return or a tight passage.

A recessed box is built into the wall so its door sits roughly flush with the finished face. This is the tidiest look and the usual choice for a new extension wall, because the box can be set into the cavity or into the blockwork as the wall is built. A recessed box needs the wall thickness to take it: the box body projects back into the wall, so the builder forms an opening in the inner or outer leaf to receive it. On a standard cavity wall this is straightforward to plan; on a thin or single-skin wall there may not be depth for a fully recessed box.

A semi-recessed box is the middle option. Part of the body sits in the wall and part stands proud, used where the wall is not quite deep enough for a full recess but you still want to reduce how far the box projects. It is less common but useful on awkward build-ups.

Choose based on the wall and the look. For a new cavity-wall extension, recessed is usually the right call: it builds in cleanly during blockwork and finishes flush. For a solid wall, a retro-fit onto an existing wall, or where there is no depth to recess into, surface-mounted is the honest answer.

The back plate, the duct entry, and building it in plumb

Two details inside the box decide whether the meter move actually works on the day.

The back plate is the panel at the rear of the box that the meter and the supply head fix to. The network needs the right back plate for the meter they are installing, so the box type has to match the supplier's requirements rather than just being "a box that fits". Order the box the network or supplier specifies, not a generic one, and confirm the back plate is included rather than a separate part.

The duct entry is the opening at the base of the box where the supply enters. The gas pipe or the electric service cable runs up through a duct from the ground, in through the base of the box, and onto the meter. The builder has to leave that duct in place as the wall goes up, with the box positioned over it, so the supply has a clear route in. Build the box with no entry left for the duct and the network engineer arrives to find nowhere to bring the supply in: a wasted visit and a rebooking weeks later.

The box also has to be built in plumb and level, and at a sensible height. A meter reader has to reach the meter and read it, so the box wants to sit at a comfortable standing height, not down at ankle level or up out of reach. Networks publish height ranges for meter positions; build it too high or too low and the move can be refused on the day. The builder sets the box during blockwork, checks it for plumb with a spirit level as the surrounding courses go up, and beds it so it is not racked or twisted in the wall.

Standard sizes, colours, and locks

Gas and electric boxes each come in a small set of standard sizes. The common UK domestic gas box is a recognised size built around a standard gas meter, and the common recessed electric box is around 595mm tall by 409mm wide by 210mm deep, sized for a single-phase domestic meter and service head. Three-phase electric supplies need a larger box. The point is that these are standard parts: match the box to the meter type and you will not be guessing dimensions.

White is the default door colour, with cream and brown stocked to blend with render or brick. The door locks with a triangular meter key, the standard utility key that fits gas and electric boxes across the country. You can buy one cheaply from any merchant, but you will rarely need it: the network and meter reader carry their own. Locks and hinges on a decent box are heavy-duty and weather-resistant, because the door is exposed to the weather for decades.

Cost and where to buy

The box itself is one of the cheapest parts of the whole meter relocation. The expensive part is the network and supplier work to move the meter, covered on the meter relocation page. A homeowner or builder typically buys the empty box from a builders' merchant or a specialist meter-box supplier; the prices below are current UK retail, including VAT, for the common domestic types.

Prices in the table above are from UK specialist meter-box suppliers and builders' merchants stocking gas and electric boxes. A standard domestic box is an inexpensive part; if you are paying much more than the figures above you are likely looking at a three-phase box, a metal cover, or a bespoke size you do not need. Builders' merchants such as Travis Perkins and Selco stock the common types, and specialist suppliers carry the full range plus replacement doors if you only need to swap a damaged cover rather than the whole box.

Buy the box that matches the meter and back plate your network specifies. A replacement door or frame is far cheaper than a whole box, so if an existing box is sound but the door is cracked or sun-damaged, a new door alone does the job.

Who fits it and who connects it

This is the split that trips people up, so it is worth being blunt about. The builder fits the empty box into the wall during blockwork: positions it over the duct, builds it in plumb, and makes it weathertight. The energy supplier moves the meter itself into the box. The gas or electricity network moves and reconnects the supply (the pipe or the cable) to the meter.

You cannot move a live meter yourself, and neither can your builder. Disconnecting and reconnecting a gas or electric supply is work only the network and supplier are permitted to do. The builder builds the box in and leaves it empty, ready; the meter goes in later, on a booked appointment, done by the people allowed to do it.

That booked appointment is the bottleneck. Suppliers and networks run their own booking systems with their own queues, and lead times of several weeks to a few months are normal once you factor in survey, quote, payment, and scheduling. The box being ready on the wall does nothing to speed that up. The work has to be arranged early, well before the wall is even built, so the meter move can slot in when access allows.

Weatherproofing, drainage, and venting

A meter box sits outside for the life of the building, so it has to shed water and breathe. The door overlaps the body to throw rain off, and the box drains through weep points at the base so any water that does get in runs out rather than sitting on the meter.

For a gas box, venting is not optional. The box must vent top and bottom so that any escaped gas can disperse rather than build up inside a sealed enclosure. Never seal a gas box airtight with foam, mastic, or render packed around the door: blocking the vents removes the safety function the box is built around. The duct entry at the base is sealed against the duct itself to stop draughts and vermin, but the box vents stay clear.

An electric box does not vent for gas safety but still needs its base entry and weep points clear so condensation drains. Pack the box solid with insulation or render and you trap moisture against the meter and tails, which is the opposite of what you want.

Building it in: the sequence

The order the box gets built in matters, because it has to be in place and ducted before the wall closes up and before the meter can be moved.

Common mistakes

Building the wall before arranging the meter move. The most expensive mistake. Supplier and network lead times run to weeks or months, and the box being ready on the wall does nothing to shorten them. Start the meter relocation paperwork early, before the wall is built, so the connection can be booked in.

The wrong box size or type. Buying a generic box that does not match the meter or the back plate the network needs means a refused move on the day. Confirm the type with the network before ordering.

No duct or entry left for the supply. Building the box in with no opening at the base for the gas pipe or electric cable leaves the network engineer with nowhere to bring the supply in. The duct has to go in as the wall is built.

Fitting it too high or too low. A meter reader and engineer have to reach the meter. A box built down at the skirting or up out of reach can have the move refused. Set it at a sensible standing height to the network's range.

Sealing a gas box airtight. Foam or mastic packed around a gas box to "neaten" it blocks the vents the box needs to disperse a leak. Gas boxes must vent. Leave the vents and weep points clear.

Assuming the builder can connect the meter. The builder builds the box in. Only the supplier can move the meter and only the network can reconnect the supply. Treating the box being built in as "job done" leaves the actual connection unbooked, and that is where the long lead time bites.

Where you'll need this

• Utility meter relocation - the box is built into the new wall to house the relocated gas or electricity meter, and must be arranged early because the supplier and network lead times are long

An external meter box is built in on any extension or renovation where a gas or electricity meter has to move to a new external wall. The box is a cheap, standard part fitted by the builder during blockwork, but the meter move and final connection are done by the energy supplier and the network on their own timescale, so the work has to be booked well before the wall goes up.