Quality Workmanship
Built to last, not just to look finished on handover day.
Extension builders • London
Extension Builders in London
A building extension isn't one job — it's eight, stacked end to end, each depending on the one before it being done properly. Here's the actual sequence, managed by one team from first visit to completion certificate.
- Skilled tradespeople in every discipline
- Meticulous attention to detail
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Tell us what needs doing and we'll come back with a written, itemised quote — no obligation to proceed. Prefer to talk it through in person? We're happy to arrange a free site visit.
A building extension is the biggest single project on this list, and the one that most exposes the difference between a coordinated build and a collection of separate trades working in sequence without anyone actually managing the sequence. It isn't one job — it's eight, stacked end to end, each depending on the one before it being done properly. Miss a step, or do it out of order, and the whole schedule absorbs the delay. Here's the actual sequence, in the order it genuinely happens on site.
01
Initial Consultation & Feasibility
Before any drawings exist, the first visit establishes whether the extension being imagined is actually achievable on the site in question — access for construction vehicles and materials, whether neighbouring boundaries and party walls are involved, what's underground that a design will need to route around rather than through. Realistic budget expectations get set against the scope being discussed at this stage, rather than left until a full design has already been drawn up around an unrealistic figure. This is also where a rough sense of timeline gets established, so the rest of the process isn't measured against an assumption nobody actually confirmed.
Timeline: 1–2 weeks
02
Design & Planning Permission
Most single-storey rear extensions fall under permitted development rights and don't need full planning permission, provided they stay within specific size and position limits — but side-return extensions, anything exceeding permitted development thresholds, or properties in conservation areas often do need a full application. Getting this classification right at the design stage, rather than assuming, avoids a stalled project months in. Drawings at this stage cover both the planning submission (if needed) and enough detail for a structural engineer to start work in the next step, rather than two separate, disconnected design exercises.
Timeline: days (permitted development) to 8+ weeks (full application)
03
Building Regulations & Structural Engineering
Separate from planning permission, every extension needs building regulations approval — structural calculations for foundations, beams and load-bearing work, signed off by a structural engineer and submitted to building control. Party wall agreements with neighbours also get sorted at this stage if the extension affects a shared wall or boundary, a legal process with its own notice periods, not something that can be skipped or rushed.
Timeline: 2–4 weeks, often running alongside planning
04
Groundworks & Foundations
The physical build starts below ground: excavation to the depth the structural engineer's specified, foundation pour, and drainage work, particularly if the extension affects existing drain runs that need diverting. Ground conditions on London plots are inconsistent enough that what the structural design assumed and what's actually found on excavation don't always match — the single most common source of a quote's estimate shifting once work is genuinely underway.
Timeline: 1–2 weeks
05
Structural Build
Brickwork or blockwork walls go up, steel beams get installed where openings are being created — most commonly where the extension joins the existing structure — and the roof structure goes on. This is the stage where the extension genuinely becomes a visible, weatherproof shell rather than a hole in the ground with foundations in it, and getting the roof on and watertight as early as possible protects everything that follows from weather delays. Matching brick or render to the existing property, where that's the brief, gets decided and sourced during this stage too, since matching materials can have their own lead times separate from the build itself.
Timeline: 3–5 weeks (longer for two-storey)
06
First Fix
With the shell weatherproof, electrics, plumbing and any structural carpentry get roughed in behind what will become finished walls, alongside windows and external doors being fitted. Roofing details — flashing, guttering — get finished properly at this stage too, since it's far harder to correct roofing work once the extension's plastered and decorated around it.
Timeline: 2–3 weeks
07
Second Fix & Finishing
Plastering, flooring, and final decoration bring the extension to a genuinely finished state, followed by second-fix plumbing and electrics — sockets, switches, fittings actually connected and tested — once walls are painted and floors are down. This stage determines whether the extension reads as a natural continuation of the existing property or an obviously separate addition, particularly where flooring and trims need to match what's already there, or where a bifold door or large glazed opening is bridging the two spaces and needs to look considered rather than bolted on.
Timeline: 2–3 weeks
08
Building Control Sign-Off & Handover
A final building control inspection confirms the completed work meets the regulations it was designed against, resulting in a completion certificate — a document worth keeping indefinitely, since it's frequently requested when a property is eventually sold. A final walk-through and snagging session happens alongside this, before the project is genuinely considered finished rather than just physically complete.
Timeline: 1–2 weeks after practical completionEight steps, four to six months, one project manager holding the sequence together throughout — that's the honest shape of a house extension in London. The steps that get skipped or rushed on a badly-run project are almost always the invisible ones: the structural sign-off, the party wall notice, the drainage diversion nobody budgeted for. None of them show up in a finished photo, and all of them determine whether the finished extension is genuinely sound or just looks that way.
Frequently asked
Questions Before You Get In Touch
Do I need planning permission for a house extension in London?
Often not, if the extension falls within permitted development rights — specific size and position limits apply, and these get confirmed during the initial consultation. Extensions exceeding those limits, some side-return extensions, or properties in conservation areas typically do need a full planning application.
How much does a house extension cost in London?
Cost varies enormously with size, structural complexity and finish specification — a single-storey rear extension sits at a very different price point to a two-storey addition. A written, itemised quote follows the initial feasibility visit, with no obligation to proceed.
How long does a house extension take from start to finish?
Including planning and building control processes, a typical single-storey rear extension realistically takes four to six months start to finish; the on-site build itself is usually ten to sixteen weeks of that.
Do I need a party wall agreement for my extension?
If the extension affects a shared wall or boundary with a neighbouring property, yes — this is a legal requirement with its own notice periods, sorted alongside the structural design stage rather than left until construction is about to start.
Can I live in my house while the extension is being built?
Usually yes, particularly for a single-storey rear extension where the existing property stays largely unaffected — though there will be periods of noise, dust and restricted access to parts of the house, especially where the extension connects to an existing room.
What's the difference between permitted development and full planning permission?
Permitted development rights allow certain extensions within defined size and position limits without a full planning application, though written confirmation is worth obtaining even so. Anything outside those limits needs a full planning application, typically taking around eight weeks for a decision.
London Areas We Cover
End-to-End London Home Renovation Coverage
The areas below are examples, not a complete list. Kay Home Renovation takes on projects right across Greater London, whatever your postcode — if you don't see your area named, get in touch anyway; it's very likely still covered. Whether it's a single room that needs freshening up or a full interior-exterior renovation from start to finish, the same team sees it through, from the first survey to the final handover.
East London
- Ilford
- Redbridge
- Barking
- Romford
- Wanstead
- Woodford Green
- Chigwell
North London
- Islington
- Enfield
- Barnet
- Haringey
- Tottenham
- Muswell Hill
- Finchley
South London
- Croydon
- Bromley
- Lewisham
- Greenwich
- Wandsworth
- Clapham
- Dulwich
West London
- Ealing
- Hounslow
- Hammersmith
- Richmond
- Uxbridge
- Chiswick
- Acton
Central London
- Westminster
- City of London
- Southwark
- Kensington & Chelsea
- Camden
- Marylebone
- Holborn
These are examples from each region, not an exhaustive list — Kay Home Renovation covers the whole of Greater London.
Why Kay Home Renovation
Skill & Quality
Attention to Detail
Real care taken over the quality of the finish, not just the speed of getting it done.
Reliable Timelines
Projects completed to the schedule agreed at the outset, not an optimistic one designed to win the job.
Fair Pricing
Written, itemised quotes with no inflated figures and no unwelcome surprises once work begins.
Consistent Standards
The same standard of finish across every trade, not just the ones on show.
Snag-Free Handover
Nothing signed off until it's actually right, not just close enough.
Get a free quote
Request Your Free Quote
Fill in a few details and we'll come back with a written, itemised quote — no obligation to proceed. Prefer to talk it through in person? We're happy to arrange a free site visit.
- Phone
- 07735 939986
- 07735 939986
- enquiry@kayhomerenovation.co.uk
- Based in
- 58 Peregrine Road, Hainault, Ilford, IG6 3SZ
- Hours
- Mon–Fri 08:00–18:00, Sat 09:00–14:00