Plumbery
House extension builders in London
Kitchen, rear, side-return and wraparound extensions in London, with the build, plumbing, electrics, heating and fit-out handled by one team.
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- One team for every trade
- Written estimate before work starts
- Gas engineers and qualified electricians
Starting prices
House extension prices: what the starting package includes
From £1,900 per m²
A simple single-storey rear extension: foundations, blockwork walls, flat roof, standard insulation, uPVC window and door, plastered and painted walls, basic sockets and lighting, and a radiator. A 15 m² extension on this specification starts from about £28,500.
Popular upgrades
Bi-fold or sliding doors, roof lights or a roof lantern, underfloor heating, a pitched roof, and a new kitchen or shower room inside the extension.
What costs extra
Drawings, structural engineer, planning and building control fees, steel beams to open up the back of the house, moving drains and party wall costs. Each one is itemised in your written quote. All starting prices include VAT.
House extension London
House extensions in London, from planning checks to the finished room
Most extensions go wrong in the gap between trades: the builder finishes the shell, then the plumber, electrician, plasterer and kitchen fitter all have to be found and scheduled. Plumbery builds the extension and does the plumbing, electrics, heating and fit-out itself, so one team is responsible from the foundations to the last socket.
In London the typical project is a rear or side-return kitchen extension on a Victorian or Edwardian terrace, where party walls, shared drains and conservation areas all need to be dealt with before the build starts. We check these on the first visit.
Our clients
Design-led extensions for homes that want it done once
Our London extension clients are mostly in Victorian and Edwardian houses in boroughs such as Islington, Hackney, Camden, Wandsworth, Lambeth, Richmond and Kensington and Chelsea. They want a finished kitchen-diner, not just a shell: slim-frame glazing, roof lights, underfloor heating, a kitchen island and lighting designed with the room.
We take on a limited number of extensions at a time and keep one project lead on each, so you deal with one person from the first drawing to the building control completion certificate.
What we build
Extension projects we take on
Kitchen extension
A bigger kitchen and dining room at the back of the house, often with roof lights and sliding or folding doors.
Side-return extension
Filling the side passage of a terraced house to widen a narrow kitchen.
Wraparound extension
Combining a side-return and a rear extension into one L-shaped open-plan space.
Single-storey rear extension
Extra living space, often within permitted development limits.
Garden room and annexe
A separate insulated room in the garden, with power, heating and, where needed, a shower room.
Extension fit-out
Plastering, underfloor heating, electrics, flooring and a new kitchen or bathroom in the new space.
How it works
How a house extension runs, step by step
Survey and feasibility
We look at the house, garden, drains, boundaries and any conservation area, and tell you what is realistic before you pay for drawings.
Drawings and approvals
Planning permission, prior approval or a lawful development certificate as needed, structural calculations, building regulations and Party Wall notices.
Groundwork and drainage
Excavation, foundations and any drain diversions, inspected by building control.
Shell and roof
Walls, steel beams, roof, roof lights and glazing to make the extension weathertight.
First fix
Plumbing, heating, electrics and data run before plastering.
Fit-out
Plastering, flooring, kitchen or bathroom installation, decoration.
Sign-off and handover
Building control completion certificate, electrical and gas certificates, and a full clean.
Planning
Planning permission, permitted development and party walls
Many single-storey rear extensions in England can be built under permitted development: up to 3 metres deep on a terrace or semi and 4 metres on a detached house, or up to 6 and 8 metres through the prior approval process, within height and boundary limits. Side-return and wraparound extensions, flats and maisonettes, and houses in conservation areas or under an Article 4 direction usually need full planning permission, which is common in inner London boroughs.
Every extension needs building regulations approval. On most London terraces the work is on or close to a party wall, so the Party Wall etc. Act 1996 requires notice to your neighbours before work starts. We plan this into the timetable.
Cost and time
What a house extension costs and how long it takes
The cost depends on the size, the foundations and ground conditions, the roof and glazing, steelwork, and above all the fit-out: a kitchen extension costs more than a living room of the same size. Use the house extension cost calculator for a budget with labour, materials and VAT.
A single-storey rear extension typically takes around 10 to 16 weeks on site once approvals are in place. Planning decisions usually take about 8 weeks, and Party Wall notices need at least one to two months, so we start these early.
Beyond London
Extensions within 200 miles of London
Our team also takes on bathroom, kitchen and extension projects within about 200 miles of London. See the towns and cities we cover.
Questions
House extension in London: your questions
Do I need planning permission for a house extension in London?
Not always. Many single-storey rear extensions fall under permitted development, but side-return and wraparound extensions, flats, and houses in conservation areas or under an Article 4 direction usually need planning permission from the borough.
How long does a house extension take?
A single-storey rear extension usually takes around 10 to 16 weeks on site, plus the time for drawings, approvals and Party Wall notices beforehand.
How much does a house extension cost in London?
It depends on size, foundations, glazing and fit-out. Our house extension cost calculator gives a budget with VAT, and the survey turns it into a written estimate.
Do I need a party wall agreement?
If you build on or near a shared wall or boundary, or dig foundations close to a neighbour, the Party Wall etc. Act 1996 requires you to serve notice. Most London terrace extensions need it.
Can you fit the kitchen in the new extension?
Yes. We build the extension and fit the kitchen, plumbing, electrics and heating, so one team is responsible for the whole job.
Can I live in the house during the build?
Usually yes. The new extension is built while the back wall stays in place, and the opening is made near the end, so disruption inside is limited to a few weeks.
Do you build extensions outside London?
Yes, within about 200 miles of London, including Birmingham, Bristol, Manchester and Leeds.
Why Plumbery
Qualified, insured and upfront about price
Every engineer we send is registered or qualified for the trade they work in, and you can check the details before anyone starts.
- Fully insuredEvery job is covered by our insurance.
- Rates published in advanceOur hourly rates are on the pricing page. Nothing starts until you agree the rate.
- Paperwork includedGas safety certificates and electrical records are provided on completion.
- Registered companyPlumbery Ltd, company no. 11677583, registered in England and Wales.
Choosing a type
Rear, side-return or wraparound: which house extension suits your London home?
Most London houses have a narrow footprint, so the shape of the extension matters as much as its size. A rear extension pushes the back wall into the garden and suits houses with decent depth. A side-return extension fills the thin alley beside an Edwardian or Victorian terrace, usually turning a dark galley kitchen into a wide, bright room. A wraparound combines the two for the biggest gain in floor area.
A double-storey extension adds a bedroom or bathroom above the new ground floor and is often better value per square metre, because the foundations and roof are shared. We walk through the options on site, check how each one affects the garden, light and neighbours, and put the choice in writing before any design work starts.
Kitchen extensions
Planning a kitchen extension that works every day
A kitchen extension is the most common reason Londoners build out, and it goes wrong when the layout is decided last. Agree where the sink, hob, fridge and island sit before the structural openings are fixed, because that decides where drains, gas, extraction and sockets must run under the slab and through the walls.
Think about daylight from the rear garden and from above. Rooflights and large sliding doors bring in light, but they also add heat gain in summer and heat loss in winter, so the glazing choice affects comfort and energy bills. Our team can fit the kitchen itself, so one programme covers the build, the first fix and the finished room. See also our kitchen refurbishment service.
Structure and rules
What a London extension has to get right
Structural design
Opening up the back of the house usually means steel beams and padstones, designed and calculated by a structural engineer and checked by building control.
Building Regulations
Foundations, drainage, fire safety, ventilation, insulation and electrics are all inspected. Planning permission does not replace this approval.
Drains and sewers
Building close to or over a public sewer or drain normally needs the water company's agreement, so we check the drainage plan early.
Energy performance
New walls, roof, floor and glazing must meet current Part L energy requirements, which also helps keep the room warm and the bills sensible.
Heating and electrics
Radiators, underfloor heating and new circuits must be designed in from the start, with electrical work to BS 7671 and notified where required.
Permitted development
Can you build under permitted development in London?
Many single-storey rear extensions can go ahead without a full planning application if they stay within permitted development limits on depth, height and materials. Larger single-storey rear extensions can sometimes be approved through the prior approval route, where neighbours are consulted. Flats and maisonettes do not have these householder permitted development rights, and your own house may have had them removed by a planning condition or an Article 4 direction.
Conservation areas, listed buildings and homes covered by an Article 4 direction are the usual traps in London, where side extensions and changes to the front are heavily restricted. A lawful development certificate from the council gives written proof that your plan is permitted. We can tell you which route is likely before you pay for drawings.
Before you start
Preparing your house for an extension
- Tell your mortgage lender and buildings insurer about the works
- Clear the back of the house, the garden path and the side access
- Decide where you will cook, wash and sleep during the build
- Check where the gas, water and electric meters and the stopcock are
- Agree access and parking arrangements with neighbours and the council
- Pick finishes such as flooring, tiles, doors and lighting early
- Photograph the existing rooms, boundary walls and fences
Planning
Design, drawings and approvals before the build
A good extension is decided on paper first. The usual sequence is measured survey, concept layout, planning or lawful development drawings if needed, structural calculations, then full Building Regulations drawings. Skipping any of these is what causes mid-build changes and delays.
Some projects also need a drainage survey, a tree check or party wall notices to your neighbours under the Party Wall etc. Act 1996, served one or two months before the relevant work, with a party wall award if a neighbour does not consent. Doing these at the design stage keeps the programme honest. If you already have drawings from an architect, we will price from them, and if you do not, we can talk you through who you will need and in what order.
On site
What happens on site, stage by stage
Groundworks
Set-out, excavation and foundations are inspected by building control before concrete is poured.
Structure
Steel beams are fitted, the back wall comes out and the walls and floor slab go up under temporary support.
Roof and weathertight
The roof, rooflights and windows go in so the new space is dry before internal work begins.
First fix
Plumbing, heating, electrics and drainage are run in before plastering hides them.
Plaster and finishes
Plastering, screed, flooring, kitchen fitting, decoration and final connections follow.
Inspection and handover
Building control signs off, certificates are issued and we walk through the finished room with you.
Living with the build
Dust, noise and neighbours: managing a house extension
Building out the back of an occupied house is disruptive, and it helps to plan for that. The opening-up stage is the dustiest, so we protect floors and seal doorways. Water, power and heating are usually switched off for short, agreed periods rather than for days, and we tell you in advance when this will happen.
Good neighbour relations make a real difference in a terrace. Let neighbours know what is happening and when, agree working hours that fit your council's rules, and keep the site tidy. Skip hire, deliveries and access through the house are planned in advance so the street is not blocked.
What affects cost
What affects the cost of a house extension
The size of the footprint is only part of the story. Ground conditions, the number of storeys, the width of structural openings, the glazing specification, roof type, drainage diversions and the standard of the kitchen all move the total. Access also matters: a terrace with no side entrance means materials come through the house, which takes more time.
The most reliable way to budget is to separate the build, the fit-out and the professional fees, then add a contingency for what is hidden behind walls and under the ground. Use our house extension cost calculator for a first range, check the pricing page for what is included, or book a free survey for a written estimate based on your own house.
Adding value
Extension or loft conversion: which adds more?
Both add living space without the cost and disruption of moving. An extension tends to improve the daily way a home works, particularly the kitchen and garden link, while a loft conversion usually adds bedrooms and a bathroom without touching the garden. Many London families eventually do both.
Whichever you choose, the biggest return comes from space that suits the house and neighbourhood, and from good quality construction and finish. If you want to compare, we can price the two side by side during the same survey visit, and our house renovation cost calculator helps with the wider picture.
Ground conditions
London clay, trees and foundations for an extension
Much of London sits on clay, which swells when wet and shrinks when dry. Tree roots take moisture from it, so mature trees near the back of a house, or a tree that has been removed, can change how the ground behaves. That is why foundation depth is decided from the soil, not copied from a neighbour's extension.
A structural engineer will usually ask for trial pits or a ground investigation, check where trees stand relative to the house, and design foundations accordingly. Trenches may need to be deeper near trees, and sometimes a more robust foundation type is used. It is dull work, but it is the part that stops cracks appearing a year later, so it is worth raising early with your designer.
Building Control
Building Control routes, inspections and completion paperwork
Building Regulations approval is separate from planning. You can use the local council's building control team or a private registered building control approver. Since April 2024, private building control work can only be carried out by approvers registered with the Building Safety Regulator, which replaced the old approved inspector system, so check the public register before you appoint one.
Either route involves a plan check and inspections at key stages, normally including foundations, drainage, structure, insulation and final completion. Your builder usually books these, but you should know which stages are coming, because covering work up before it is seen can mean opening it again.
At the end you should receive a completion certificate from the council, or a final certificate if you used a registered building control approver, together with structural calculations, electrical certificates and any glazing or product documents. Keep them together. Buyers, lenders and insurers ask for them, and an update to your energy performance certificate may follow.
Covenants and leases
Covenants, leasehold rules and local charges to check first
Planning permission and Building Regulations are not the only permissions. Many London freehold houses carry restrictive covenants in the title deeds that limit what can be built, and some estates have rules about extensions. Check the title documents early, as a covenant can be enforced even if the council has approved the plan.
If your home is leasehold, including a house on a long lease or a ground-floor maisonette, the lease may require written consent from the freeholder before any structural work. A flat rarely has the right to extend into shared land, so this route is much more limited.
The Community Infrastructure Levy, charged by many councils and in London also by the Mayor, can apply to new floor space. A householder extension adding less than 100 square metres of internal floor area is normally not liable. A larger extension to a home you own and live in can usually be exempt, but the exemption must be claimed and the council's forms, including a commencement notice, sent before work starts, otherwise the full levy can become payable. Ask your council which rules apply. These checks cost nothing to do early and can save a design from being redrawn. When you are ready, you can book a survey or look at the pricing page.
Price calculators
Work out the cost of your project online
Start with our extension cost calculator, or choose another project below. Each calculator has its own page. The estimate includes labour, materials and VAT, and you see it without leaving your details.
