Modular Extensions London
Made in a factory, craned over the roof, and weathertight in days: an extension for a London terrace without months of skips in the street.
Get a quote- £2,500 to £4,600
- per m² for a finished modular extension in London, including VAT. National ranges with a 20 to 40% London allowance; a guide, not a quote.
- About £1,400
- for a one-day contract lift with a 25 tonne crane and its crew, before any borough charge for the parking bays.
- £548
- householder planning fee in England from 1 April 2026, if your street needs an application.
Sources and how we use them
A guide, not a quote. Typical national ranges for 2026 including VAT, with the usual London allowance of 20 to 40% added. Build rates come from 2026 national cost guides; fees are set by MHCLG from 1 April 2026.
Built for streets with no way round the back
Most London terraces have no side gate. A brick extension means every block, bag and steel beam carried through the hall. A modular one arrives on a lorry and goes over the roof in a morning.
That lift is the part to plan. The crane needs two or three parking bays suspended by the borough, a clear swing over the house, and a firm standing on a road that may be narrow, sloping or a bus route. Get those right and the rest is quicker than a traditional build.
From first visit to lift day
The factory time runs alongside your paperwork and groundworks, which is where the weeks are saved.
Survey the street
The builder measures the house, checks the crane position and the drains, and looks at the ground.
Permission and neighbours
Planning or a lawful development certificate, party wall notices and, over a public sewer, a build over agreement.
Factory and foundations
Modules are made indoors while the crew digs and pours the foundations at home.
Lift and finish
One crane day, then joining, roofing, electrics and decoration inside the house.
Want a figure first? The London cost calculator prices your size and finish, then carries both into the form.
Questions London owners ask
Can a modular extension go on a London terrace with no side access?
Usually, yes. The modules or panels are lifted over the roof by a mobile crane parked in the street, so nothing has to come through the house. The crane needs a parking suspension, and on narrow or busy roads sometimes a short road closure, both arranged with the borough. See parking suspensions and crane access.
Is a prefab home extension in London cheaper than a brick one?
Not by much per square metre. Finished modular prices sit close to a traditional build. The saving is time: most of the work happens in a factory, so the street, the neighbours and your kitchen put up with a few weeks of site work, not a few months.
Do I need planning permission?
A modest single-storey rear extension is often permitted development, but not in every London street. Conservation areas and Article 4 directions remove some rights, and flats have none. A full householder application in England costs £548. See planning in a conservation area.
Will I need a party wall agreement?
If you dig foundations within 3 metres of a neighbour’s building, or build on or against the party wall, the Party Wall etc. Act 1996 applies, which is almost always the case on a terrace. A surveyor typically costs £700 to £1,500 per neighbour where one surveyor is agreed.
Get a quote for your extension
Postcode, four quick questions, then your contact details. It takes about a minute.
We are an introduction service, not a builder. We look for a firm that works in your borough, tell you who it is, and pass your details on only when you say yes.
Got it. Thank you.
- We look for an extension builder who takes on jobs like yours in your part of London, and we email or phone you with the firm's name.
- If you are happy with that firm, we send it what you told us. If not, nothing goes anywhere.
- The firm arranges a visit, looks at the access and the ground, and gives you its price.