Modular extension cost per m²
One rate, multiplied by the floor area, is how most people first size up an extension. Here is the 2026 rate for modular work, what is inside it and why two firms can quote £1,000 a metre apart for the same room.
What the rate buys
The figure is for a finished, heated, wired room joined to your house. It takes in the structure, insulation, roof covering, windows and external doors, plaster, electrics, a concrete base on ordinary ground, transport from the factory and a mobile crane for a day.
VAT is in it. It does not take in the fees for drawings and approvals, a new kitchen, or anything the ground or the street throws up. Those are set out on the page about what a price includes.
The range is wide because it has to hold a plain garden room with one set of French doors and a kitchen with five metres of sliding glass and a lantern over the table. Both are single-storey modular extensions.
Which square metres?
A rate means little until you know what it is multiplied by. Some firms measure the footprint from the outside of the walls. Others use the floor you can stand on.
Take a room that measures 4 m out from the house and 5 m across on the outside: 20 m². With walls 300 mm thick on three sides, the floor inside is 3.7 m by 4.4 m, or a little over 16 m². Quote the same room at the same total and one firm's rate looks nearly a fifth cheaper than the other's.
Ask for the internal floor area in writing and divide the price by that. It is the number you will live in.
What moves a quote within the range
Glass. Wide sliding doors, corner glazing and rooflights cost several times as much per metre as the insulated wall they replace, and large panes can limit how a module is lifted.
Wet rooms. A kitchen or shower room needs drains, hot water and extraction. An open living space needs sockets and a radiator.
Finish. Brick slips or zinc outside, engineered timber underfoot and plastered-in lighting all sit at the upper end. Render, laminate and standard downlights sit lower.
Shape. A rectangle that travels as one piece is the cheap case. An L-shape, or a room wider than a lorry can carry, is built as two modules with a joint to finish at your house.
What sits on top of the rate
| If this applies | Typical effect |
|---|---|
| The house is in London or the South East | 20 to 40% more |
| The crane needs a second day A lift over the house, a long reach or a road that has to be closed | about £1,400 a day |
| A new kitchen goes in | £15,000 to £35,000 |
| A shower room goes in | £5,500 to £9,000 |
| Clay, trees or made ground need piles Designed by the engineer after a ground investigation | several thousand pounds |
National guide figures, VAT included. The calculator adds the first three for you.
Why a small room costs more per metre
Some costs ignore size. A contract lift, meaning the crane, its operator and the crew who sling and guide the module, is about £1,400 for the day whether it lifts 12 m² or 40 m². The lorry makes one trip. The hole in the back wall of the house needs the same steel beam.
Spread that lift over 12 m² and it adds about £117 to every metre. Over 40 m² it adds £35. That is why a compact utility room tends to be quoted near the top of the range and a large family room nearer the middle, even at the same finish.
Two storeys
We do not give a per-metre figure for two-storey modular extensions, because we have not found a published one we would stand behind. The principle is simple enough: the foundations and the roof are bought once and shared between two floors, so the rate for each square metre normally falls. The crane is bigger and the lift takes longer, which gives some of that back. Ask for a quote.
Against brick and block
An extension built on site in brick and block typically runs £2,200 to £3,200 per m². The two bands sit almost on top of each other. Modular pays for factory time, transport and the lift; it buys a build that spends far less time in your garden. The comparison page works through a 20 m² example.
Where these figures come from
Typical national ranges for 2026, VAT included. Expect 20 to 40% more in London and the South East. A guide, not a quote. Rates per square metre, the crane day, fit-out costs and the regional uplift are typical ranges from UK cost guides published during 2026. The inside and outside measurements are our own arithmetic for a 300 mm wall. The rules referred to are on the pages below.
Cost per m² questions
What is the cost per m² of a modular extension in 2026?
£2,100 to £3,300 for a single storey, finished, with a standard base, delivery and a one-day crane lift in the figure and VAT included. These are national ranges.
Is the rate worked out on inside or outside measurements?
It depends on the firm, and the gap can be a sixth of the floor. Ask each one which it uses and compare quotes on internal floor area.
Does a bigger extension cost less per m²?
Usually a little, because the crane, the lorry, the opening into the house and the council fees are much the same whatever the size. Nobody publishes a reliable sliding scale, so our tables use one band for every size.
Do the rates apply in Scotland and Wales?
Yes, as a guide: they are UK-wide figures. Planning rules and fees differ in Scotland, where you also need a building warrant before work starts.
Get a quote for your extension
A guide figure only goes so far. Tell us where the house is and what you want built, and a builder can price the real thing.
Your pick:
This site is a free introduction service, not a builder. We look for a firm that builds modular extensions where you live and tell you its name. Your details go to that firm only once you say yes.
Thank you. We have your request.
- We look for a builder that makes this kind of extension and works in your postcode, then ring or email you with its name.
- Nothing is passed on unless you tell us to go ahead.
- The builder visits, looks at the ground and the street, and gives you a price in writing. We never send marketing.