Residential
House extensions in London, built under one contract
Rear, side-return, wraparound and double-storey extensions. One survey, one agreed set of drawings, one fixed price, and the same crew from the first trial hole to the completion certificate.
- Fixed-price contract
- Principal contractor, CDM 2015
- In-house crew
Updated October 2026
A house extension in London adds floor area to an existing home, usually as a rear, side-return, wraparound or double-storey build. Extension builders handle the survey, approvals and construction. MO Team builds from your architect's or designer's drawings under one fixed-price contract, with its own team doing the main trades and a structural engineer engaged for the structure, and hands over a building control completion certificate.
What a London extension involves
An extension suits a household that likes where it lives and needs more of it. The common London jobs are a rear extension across the back of a terrace, a side return that fills the alley beside the kitchen, a wraparound that does both, and a double-storey that adds a bedroom above. The question is rarely how big. It is how the new space meets the old one, because a full-width rear extension leaves the middle of an original house dark. The useful conversation is about rooflights, where the kitchen sits, and whether the existing rear wall comes out completely or stays as a defined threshold between old and new. The house extension cost guide sets out typical London prices for each type, from published sources.
We run every job in the same sequence. A measured survey establishes what is there, the agreed drawings and the engineer's calculations settle what is going in, a fixed price is written against a named specification, then our crew builds it and hands over the certificates. The London detail is where budgets move. Victorian and Edwardian foundations are shallow by current standards and the new ones go deeper, deeper still within influencing distance of a mature tree on clay subsoil. Drainage often crosses the footprint, and building over a public sewer needs an agreement with the water company rather than a decision on site. Party wall notices carry statutory periods that cannot be shortened. Skip permits, suspended parking bays and low traffic neighbourhood restrictions decide how material reaches a back garden, and each borough sets its own hours for noisy work.
One team matters most on the parts nobody photographs. The groundworker who digs the trial hole and the carpenter who hangs the doors work to the same drawing as the engineer who sizes the steel, and answer to the same site manager, so a discovery in the ground becomes a priced variation the same week rather than an argument between trades. You hold one contract, one programme and one number to ring. If the workmanship is wrong, there is no argument about which trade caused it, because every trade answers to us.
What a house extension includes
A typical extension contract with us covers the following as one package, priced against a written specification.
What is in the price
How it runs
- 01
Survey and feasibility
We measure the house, look at the drainage, note any trees within influencing distance, and confirm the permitted development position for your address. You get an honest budget bracket before you have spent anything on design.
- You receive
- A written feasibility note and a budget range
- 02
Drawings and structural work agreed
Layout, glazing, roof form and how the new space meets the old are agreed in the drawings for the job. The engineer's calculations for the openings, the new floor and the roof, and a first view on foundation depth from what is visible above ground.
- You receive
- Agreed drawings and structural calculations
- 03
Fixed price and approvals
A named specification, priced line by line, with the ground carried as a stated provisional sum so you can see which part is firm and which part is not. In parallel we submit planning where it is needed, lodge the building control application and serve the party wall notices.
- You receive
- A fixed-price contract, a written specification and the submitted applications
- 04
Groundworks and shell
Trial holes first, then foundations to the depth the ground actually requires, drainage, and the structure up to a weathertight shell. Anything found in the ground is priced as a variation before it is built, never afterwards.
- You receive
- A weathertight structure and the building control inspection records
- 05
Fit-out and handover
Services, insulation, plastering, finishes, and the making good beyond the extension that people forget to budget for. We walk the snagging list with you rather than handing you one.
- You receive
- Completion certificate, warranties and a closed-out snagging list
Regulations that apply to an extension
Work of this kind
Common questions
Straight answers.
Not answered here?
Tell us what you are planning. We read every enquiry ourselves.
Ask us directly07424 445105It depends on floor area, ground conditions, the glazing specification and how much of the existing house is disturbed. Foundations and drainage move the figure more than finishes do, and neither is knowable before the trial holes are dug. Our cost guides set out the variables in detail. A firm price follows a site visit and the drawings, so you can see which part of the number is fixed.
Often not. Permitted development allows a single-storey rear extension of three metres on an attached house and four on a detached one, with six and eight metres available through the prior approval route where neighbours are consulted. Height, materials and how much garden is covered all carry limits. Permitted development is removed in conservation areas, by Article 4 directions, and for flats entirely, so the answer is address-specific.
It depends on the size, the ground and the glazing, so we give you a programme with the quote. Approvals run before the build and frequently take longer than the build itself, which is why we start planning, building control and party wall notices in parallel rather than one after another.
For a small single-storey rear extension with a simple specification it can be. For a wraparound with structural glazing it will not be. The figure is set by floor area, ground conditions and glazing rather than by ambition. Tell us the budget at the first conversation and we will say which version of the project it buys, rather than finding out together in month three.
Three metres from the original rear wall on a semi-detached or terraced house, and four metres on a detached one, under the standard allowance. The larger home extension procedure doubles both figures to six and eight metres, subject to prior approval and a neighbour consultation. Separate conditions apply to height, eaves, materials and how much of the original garden may be built on.
Almost certainly, if you are building on or near a boundary. The Act is triggered by building on the line of junction, cutting into a party wall, or excavating within three metres of a neighbouring structure to a lower depth than its foundations, which extension foundations normally do. Notice periods are one or two months depending on the section, so notices are served at design stage rather than when the crew is booked.
For a rear extension, usually yes, until the break-through. The extension is built as a separate structure alongside the house, and the disruptive phase is the few days when the existing wall is opened and the two become one space. Where the extension takes the kitchen, plan a temporary kitchen rather than improvising, because months of eating out costs more than the temporary kitchen does.
We do. We build from your architect's or designer's drawings, a structural engineer is engaged where the job needs one, and we deal with the building control inspector at each stage through to the completion certificate. Where a planning application or a party wall notice is needed we submit those too. You pay the authority fees directly, so you can see what they are.
Thinking about extending?
Send the address and a sketch, even a rough one. We will tell you what is realistic before anyone visits.