HOME EXTENSIONS & ALTERATIONS
— Extensions & loft conversions · South London
Home extensions and loft conversions across South London.
Side returns, rear extensions, loft conversions, double-storey extensions and garden outbuildings — designed, built and finished by our in-house team.
Home extensions South London — two decades of side returns transforming Victorian terraces, rear extensions opening kitchens to gardens, lofts adding bedrooms and bathrooms, double-storey home extensions on family homes. Every photograph below is from a real LMDEC project.
— Recent extensions
Extensions we’ve built across South London.
From bi-fold-doored rear extensions in Balham to loft conversions in Wandsworth and Dulwich, side returns opening galley kitchens in Clapham, and wrap-around extensions on family homes in Wimbledon and Beckenham. Every project is designed, built, and finished by our team.
— Project types
Extension types we build most often in South London.
Side return extensions
The most transformative move on a Victorian terrace — taking the dead alley space next to the kitchen and bringing it inside. Suddenly, the galley kitchen becomes an open-plan kitchen-diner with garden views. Most South London side returns we build are 2-3 metres wide and 4-6 metres long, with steel beams, structural openings, bi-fold or sliding doors, and skylights. Common in Clapham, Balham, Wandsworth, and Dulwich are Victorian and Edwardian terraces.
Rear extensions (single-storey)
Extending the back of the house into the garden — usually 3-6 metres deep. Roof lanterns or flat roofs, bi-fold doors, and structural steel where needed. Often combined with a side return for a full wrap-around. Permitted development in most cases up to 4-6 metres without planning permission (subject to neighbour consultation). Common across Wimbledon, Beckenham, Bromley, and Banstead family homes.
Loft conversions
Adding a bedroom suite or two with an ensuite under the existing roof, or with a rear dormer to maximise headroom. Steel beams, new staircase, full insulation to current Building Regs, Velux roof windows, proper fire-rated escape routes. Most lofts add 20-30m² of usable space. Dormer conversions are most common across South London for Victorian and Edwardian properties.
Double-storey and wrap-around extensions
For families needing serious extra space — extending both ground and first floor, or combining a rear extension with a side return. Almost always requires full planning permission and a structural engineer’s drawings. Adds 30-60m² of living space across two storeys. Common on larger detached and semi-detached homes in Wimbledon, Banstead, Beckenham, Richmond and Wandsworth.
Garden outbuildings and home offices
Detached garden rooms — home offices, gyms, studios, guest annexes. Insulated, plumbed and wired to habitable-room standards. Usually permitted development if under 2.5m to the eaves, within 50% of the garden footprint, and at least 1m from boundaries. Popular post-2020 for South London homeowners working from home.
— Permitted development 2025
Permitted development limits for South London lofts and extensions.
Most loft conversions and single-storey extensions in South London fall under permitted development rights — meaning you don’t need full planning permission, just a Lawful Development Certificate and Building Regs approval. The general rules for 2025:
Full UK planning permission rules and recent updates are on the official GOV.UK planning permission portal.
| Rule | Terraced / Semi | Detached | Notes |
|---|---|---|---|
| Loft volume added | ≤ 40 m³ | ≤ 50 m³ | No balconies on top floor. |
| Rear extension depth | ≤ 4 metres | ≤ 6 metres | Neighbour consultation required for larger. |
| Dormer position | Rear-facing | Rear or side | Set back from front elevation. |
| Side windows | Obscured & fixed | Obscured & fixed | Privacy rule unchanged. |
| Ridge height | ≤ 20 cm above original | ≤ 15 m total | Hip-to-gable conversions may exceed — needs planning. |
Conservation areas and Article 4 directions may remove some permitted development rights. We check this during the initial site visit.
Important exceptions: conservation areas (much of Dulwich, Wimbledon Village, Chelsea, parts of Wandsworth) have stricter rules. Article 4 directions remove permitted development rights in some boroughs. Listed buildings always need consent. Double-storey extensions and side returns usually require full planning permission. We check all of this during the initial site visit, before you commit to anything.
— What it costs
Extension costs in South London.
Honest ranges based on the extensions we’ve actually built across South London in 2025-2026. Final price depends on size, ground conditions, structural complexity, finishes specification, and whether the extension includes a kitchen or bathroom. For a quick budget range before your site visit, use our free London renovation cost estimator.
Loft conversion · £60,000 – £120,000
Standard dormer loft conversion with one or two bedrooms and an ensuite bathroom. Includes structural steel, new staircase, full Building Regs insulation, Velux windows, plastering, electrics, plumbing for ensuite, decoration. Typical project takes 8-12 weeks. Mansard or hip-to-gable conversions are at the higher end.
Single-storey extension · £80,000 – £180,000
Side return, rear extension, or wrap-around — typically 15-40m² of new floor space. Includes foundations, structural steel, brick or rendered exterior, roof lantern or flat roof, bi-fold or sliding doors, full Building Regs insulation. Add £25,000-£60,000 if including a new kitchen, depending on specification.
Double-storey extension · £150,000 – £300,000+
Full ground and first-floor extension, often combined with internal reconfiguration. Includes planning permission, structural engineer, party wall surveyor where needed, foundations, full structural shell, all internal finishes, kitchens, and bathrooms. Typical project takes 5-8 months. Add £40,000-£80,000 for high-specification finishes throughout.
Garden outbuilding · £25,000 – £60,000
Insulated garden room or home office, typically 15-25m². Concrete pad foundations, timber or SIPs construction, double-glazed windows and doors, electrics, heating, internet cabling, full plaster finish. Cheaper than a full extension and faster to build — usually 3-5 weeks on site.
Prices include construction, materials and our project management. Architect fees (£3,000-£8,000), structural engineer (£1,500-£3,500) and council fees are separate — we’ll recommend trusted partners or work with your existing team.
— How we work
Our extension and loft conversion process.
Home extensions are bigger, more complex, and more disruptive than any other home project. We’ve been building them in South London for over two decades. The process is the same whether you’re adding 15m² or 60m² — careful planning, in-house trades, fixed-price quotes, no surprises.
1. Site visit and feasibility
We come to your home, measure the site, discuss your brief, check planning constraints and party wall implications, and assess any structural challenges. You get an honest answer about what’s possible and a budget range within 48 hours.
2. Design and planning
We work with your architect or recommend one of our trusted partners. Planning applications, Building Regs drawings, structural engineer’s calculations, party wall agreements — all handled. Typical timeline: 8-12 weeks for full planning, 4-6 weeks for permitted development.
3. Fixed-price quote and contract
Once drawings and approvals are in place, we produce a fixed-price quote with everything itemised — labour, materials, finishes, contingencies. Plain English contract, stage payments tied to milestones, and a payment schedule you can plan around.
4. Build
Foundations, structural shell, roof, weatherproofing, first-fix electrics and plumbing, plastering, second-fix, kitchens and bathrooms if included, decoration, snagging. Typical extension takes 12-20 weeks. Loft conversions 8-12 weeks. Double-storey projects 5-8 months. Weekly progress meetings, daily updates, transparent timeline tracking.
5. Handover and aftercare
Final clean, walkthrough, Building Regs completion certificate, all warranties and manuals handed over. Two-year workmanship warranty. We return at six months to check the roof, weatherproofing, plaster cracks, and decoration — included.
— Why LMDEC
Why South London families trust us with extensions.
Two decades of building home extensions in South London. We know the boroughs — what planning officers in Wandsworth, Lambeth, Lewisham, Bromley, Croydon and Sutton will and won’t accept. We know the building stock — Victorian terraces, Edwardian semis, 1930s family homes, post-war detached. We don’t learn on your project.
All trades in-house. Bricklaying, structural carpentry, roofing, plumbing, gas, electrics, plastering, kitchens, bathrooms, decoration — every trade your project needs is on our team. No coordination between subcontractors. One project manager from start to finish.
Fixed-price quotes, transparent variations. Everything is itemised before we start. If the survey uncovers something hidden — old asbestos, unexpected foundations, rotten timbers — we tell you immediately, give you the costs and options, and only proceed once you’ve agreed.
£2 million Public Liability insurance. All gas work carried out by individually qualified Gas Safe registered subcontractors; all electrical work by individually qualified NICEIC certified subcontractors. Certification issued on completion where required. Registration numbers available on request for verification before work starts.
— Common questions
Home extensions South London — frequently asked.
Do I need planning permission for a loft conversion in London?
Most loft conversions in South London fall under permitted development if they stay under 40m³ for terraced/semi-detached and 50m³ for detached homes, with dormers facing the rear. You’ll still need a Lawful Development Certificate and Building Regs approval. Conservation areas (Dulwich, Wimbledon Village, parts of Chelsea) and Article 4 directions can change this — we check your address before you commit.
How long does an extension take?
Side returns and small rear extensions: 12-16 weeks on site. Larger single-storey extensions: 16-20 weeks. Loft conversions: 8-12 weeks. Double-storey extensions: 5-8 months. Add 4-12 weeks before that for planning, design and approvals depending on the project.
Can I stay in the house during the build?
For most loft conversions and rear extensions, yes — we seal off the work area, manage dust, and keep services running. Side returns and double-storey extensions usually involve weeks where the kitchen is out of action, so many clients arrange short rental or stay with family for the final stretch. We’ll be honest at the quote stage about what’s realistic.
Will a home extension add value to my home?
In South London, well-built extensions typically recoup 70-90% of cost on resale, with loft conversions often returning over 100% in higher-value postcodes like Wimbledon, Chelsea, Richmond and Dulwich. Beyond resale, the everyday value of an open-plan kitchen-diner or an extra bedroom is hard to quantify but real.
Do you handle planning and Party Wall agreements?
We work with trusted architects and party wall surveyors and can manage the entire process — planning applications, Building Regs drawings, structural engineer calculations, party wall notices. Or we work alongside your own team if you’ve already engaged an architect. Either way, you have one point of contact for everything.
What about Party Wall Act notices?
If your home extension or loft conversion affects shared walls or boundaries with neighbours, you’ll need to serve a Party Wall Notice under the Party Wall Act 1996 at least two months before work starts. If the neighbour disputes, surveyors are appointed to agree the works. We handle this whole process for you — most cases settle amicably with a simple agreement.
— Ready to start
Let’s talk about your extension.
Free site visit and detailed feasibility within 48 hours — what’s possible, what it costs, and whether you need planning permission. No pressure, no obligation.