House Extensions
Across
South London
More space, more value, less disruption. We design and build house extensions across South London — managing every stage from planning permission to final handover.
Proudly Serving South London
Planning to Handover
Free Site Consultations
The Smartest Way
to Grow Your Home
In South London — where moving costs are high and good properties are hard to come by — extending your home is often the most financially sound decision you can make. A well-built extension adds usable space, increases your property's value, and keeps you in the neighbourhood you love.
At Kelmend Construction, we manage house extensions from first conversation to final sign-off. We handle the build, coordinate all trades, and keep you informed every step of the way — so you get the space you need without the stress that usually comes with it.
What We Build
Rear Extension
The most common extension in South London. Extends your ground floor into the rear garden — typically used to open up and enlarge the kitchen, create an open-plan living and dining space, or add a utility room. Single storey rear extensions under certain sizes can often be built under permitted development, meaning no planning application required.
Double Storey Extension
Extends both the ground and first floor, effectively adding two new rooms for a fraction of what a single storey costs per square metre. Ideal if you need both a larger kitchen downstairs and an extra bedroom or bathroom above. Requires full planning permission but typically offers excellent return on investment.
Side Return Extension
Fills in the narrow alleyway that runs down the side of many Victorian and Edwardian terraces in South London. Often combined with a rear extension to create a full wraparound. Transforms dark, cramped kitchens into large, light-filled spaces — one of the most transformative extensions you can do on a terraced house.
Wraparound Extension
Combines a rear and side return extension into a single, L-shaped build. The most expansive single-storey option available, often transforming the entire rear and side of a property. Creates dramatic open-plan spaces flooded with natural light. Requires planning permission and careful structural design — exactly what we specialise in managing.
Side Extension
Builds outward into the side garden of a detached or semi-detached property. Can add a garage, utility room, home office, or extend an existing room. The footprint and design depend on your plot, the neighbours, and your local council's planning policies — all of which we help you navigate.
Garden Room Extension
A full-build extension designed to blur the boundary between inside and out — typically featuring large glazed doors or skylights, quality insulation, and integrated heating. Not to be confused with a garden office pod; this is a permanent, structurally integrated room built to the same standard as the rest of your home.
What Makes Us
Different
We Handle Planning Too
Many builders only want to build — they hand planning back to you. We advise on whether your extension needs planning permission, liaise with architects, and make sure everything is in order before a spade goes in the ground.
Itemised, Fixed Quotes
No vague estimates that balloon once work starts. We price your extension in detail so you know exactly what you're committing to. Any changes are agreed and costed in writing before we proceed.
Family-Run, Directly Accountable
You deal with us — not a project manager you've never met. We're on site, we're reachable, and our reputation depends on every job we do. That's a level of accountability larger companies simply can't offer.
Minimal Disruption
We understand you're living in your home while we build. We plan the work in sequences that minimise disruption, keep the site clean and secure every day, and protect your interior from dust and damage throughout.
Built to Building Regulations
Every extension we build is signed off by a building control inspector. This protects your investment, keeps your home insurance valid, and means you'll have no problems when you come to sell.
South London Knowledge
We know the properties, the plot types, and the planning offices across South London. Victorian terraces, Edwardian semis, post-war estates — we've worked on them all and understand the specific challenges each one presents.
Things Worth
Knowing
Extensions involve more than just building. Here are the key considerations we help you navigate from the start.
Permitted Development
Many single-storey rear extensions can be built without a full planning application under permitted development rights — saving time and money. We'll tell you upfront whether yours qualifies.
Planning Permission
Double storey, side, and wraparound extensions usually require full planning permission from your local council. We work with architects to get applications right first time.
Building Regulations
Separate from planning — all extensions must comply with building regulations covering structure, insulation, fire safety, and drainage. We manage the building control process throughout.
Party Wall Agreement
If your extension affects a shared wall with a neighbour, you'll need a party wall agreement before work starts. We'll flag this early so it doesn't delay your project.
Structural Engineering
Any extension involving removal of a load-bearing wall or significant structural work requires input from a structural engineer. We coordinate this as part of our service.
Utility Diversions
Drains, gas pipes, and electricity cables running through the proposed footprint sometimes need diverting before building work begins. We survey for this at the start.
Our Extension
Process
Free Consultation & Site Visit
We visit your home, walk the space, and discuss what you want to achieve. We give you an honest picture of what's feasible, what planning route applies, and what kind of budget you're looking at — before you've committed to anything.
Design & Planning
We work alongside your architect (or recommend one) to develop the drawings. Once finalised, we advise on the planning route — permitted development or full application — and ensure everything is submitted correctly. We can also handle the party wall process if required.
Detailed Quote & Contract
Once planning is approved and drawings are finalised, we produce a fully itemised quote. The contract is clear: scope of works, timeline, stage payments, and how variations are handled. No ambiguity.
The Build
Work starts on the agreed date. We manage all groundworks, structural work, trades, and materials. You get regular photo updates and a direct line to us throughout. The site is secured and cleaned at the end of every working day.
Finishing & Fit-Out
Once the structure is complete, we carry out all internal finishes — plastering, flooring, electrics, plumbing, decoration. We coordinate this so it flows seamlessly from the structural work, keeping the programme on track.
Handover & Sign-Off
Building regulations sign-off is obtained. We do a full snagging walkthrough with you. We don't close the job until you're satisfied — and we're always on the end of the phone if anything comes up after completion.
Covering
South London
We're based in South East London and carry out house extensions across the wider South London area. Our core patch includes:
Not listed? We cover all of South London and can travel further across the city — just get in touch.
Extension FAQs
How much does a house extension cost in South London?
A single storey rear extension in South London typically costs between £1,500 and £2,200 per square metre, depending on size, specification, and finish. A 20m² kitchen extension might range from £30,000 to £50,000 fully finished. Double storey extensions cost more in total but less per square metre, making them excellent value. We'll give you an accurate figure once we've seen your property and discussed what you want to achieve.
Do I need planning permission for an extension?
Not always. Many single storey rear extensions fall under permitted development — meaning you can build without a planning application, provided the extension meets certain size and design criteria. However, if you're in a conservation area, have an Article 4 direction on your property, or the extension is larger than permitted development allows, you will need planning permission. We'll assess this for your specific property at the consultation stage.
How long does an extension take to build?
A typical single storey rear extension takes 10 to 16 weeks from start on site to practical completion. A double storey or wraparound extension may take 16 to 24 weeks. This is build time only — planning permission (if required) typically adds 8 to 13 weeks before work can begin. We'll give you a realistic programme in your quote.
Can I stay in my home while the extension is being built?
In most cases, yes. The majority of our clients live in their homes throughout the build. We plan the work carefully to minimise disruption — particularly when we're breaking through from the existing house into the new extension. We seal off dust, protect flooring and furnishings, and always leave the site clean and secure at the end of the day.
What is a Party Wall Agreement and do I need one?
A Party Wall Agreement is a legal document required when your building work affects a wall shared with a neighbour — common with side return and rear extensions on terraced houses. You must serve notice on affected neighbours before work begins. We flag this early in the process so it doesn't cause delays, and can point you to a party wall surveyor if needed.
How much value does an extension add to a home?
A well-built extension in South London typically adds significantly more value than it costs to build. A kitchen extension or additional bedroom can add between 10% and 20% to a property's value depending on location, size, and finish. In high-value South London postcodes, the return on investment is often substantial — but the quality of the build matters enormously. A poorly built extension can cause more problems than it solves.
Let's Talk
About Your Extension
Tell us what you're thinking and we'll come to you for a free, no-obligation consultation.
No pushy sales. No call centres. Just a straight conversation about your project.