House Extensions Mitcham
Single and double storey extensions in Mitcham, planning, structure and build under one contract.
- Rated 4.9 from 31 reviews on MyBuilder
- Single-storey rear extension from £40,000
- Free site survey, itemised quote
GS Renovation builds extensions across Mitcham, from kitchen extensions on interwar terraces to rear and wrap-around extensions on the 1930s semis and post-war houses of CR4. We take a rear, side or wrap-around extension from foundations and steelwork right through to a finished, fitted room.
In Mitcham, a single-storey rear extension typically starts from £40,000, or £2,000 to £2,800 per m² (indicative London ranges, Architecture for London, Resi, MyBuilder and Checkatrade, 2026). GS Renovation Ltd, a building contractor based in Potters Bar, does the work in Mitcham: the structural engineer we appoint designs the structure, we build it, and building control signs it off.
Price guide
| Work | Indicative London range |
|---|---|
| Single-storey rear extension | from £40,000 |
| Rear extension, per m² | £2,000 to £2,800 |
| Side return, per m² | £2,400 to £3,200 |
| Wraparound, per m² | £2,400 to £3,200 |
| Double storey, per m² | £1,800 to £2,600 |
| Basement extension | see the basement page |
Indicative London ranges (Architecture for London, Resi, MyBuilder and Checkatrade, 2026), not a quotation. Prices checked September 2026. Full breakdown: Extension Costs & Planning.
Quick estimate for Mitcham
Mitcham range: choose above
Kitchen and rear extensions in Mitcham
Many single-storey rear extensions on Mitcham terraces and semis are really kitchen extensions: the back wall comes out, a steel beam carries the house above, and the old kitchen and the new space become one kitchen-diner that opens onto the garden. We begin with proper groundworks, digging and pouring foundations to suit the local ground and any nearby trees, then build the walls and set the steel beams that carry the new openings between old house and new space. Where the house has side access, a side-return or wrap-around extension widens the kitchen further, and the sink, extractor duct and drainage are set out before the slab goes down.
Double-storey extensions add a bedroom or a larger family bathroom above the new ground floor, and on the semis around Mitcham Common there is often room to do this without crowding the plot. We handle roof works, weathering into the existing pitched roof, insulation to current standards, and the full internal fit-out, so you deal with one team from the first spade to the final coat of paint.
Housing in Mitcham
Mitcham has about 10,560 homes on the Council Tax list: 10% pre-1919, 38% interwar and 51% post-war, with flats making up 46% and houses 53%. 40% of homes here are terraced; a rear extension on a terrace in Mitcham digs foundations close to both neighbours, so notices to both are normal.
Sewers and floor area in a Mitcham extension application
Before choosing how to apply, find out where the public sewer runs behind the Mitcham house. In Merton a full plans submission must be made before work starts if the proposed extension is within 3 meters of a Thames Water sewer. Building notice applications are only available for domestic projects with works not within 3 meters of one. A sewer asset search therefore belongs at the start, before the footprint is fixed. If the extension comes within that distance, allow for the full plans decision and a build over agreement with Thames Water in the programme.
Floor area matters on the application too. Merton's building control charges for extensions are set in bands, one for extensions between 10m2 and 40m2 and another for extensions over 40m2. A wrap-around on a Mitcham semi can cross that line once the side infill is added to the rear, so measure the floor area on the drawings before submitting. The same figure feeds the structural engineer's foundation layout, so settle the footprint once and use it for both rather than revising the application after the calculations change.
Planning and party walls in Mitcham CR4
Whether your Mitcham extension is permitted development or needs a full planning application depends on the property, its size and what has been added before. Many single-storey rear extensions on Mitcham houses fall under permitted development, but larger, double-storey or wrap-around schemes, and anything on a property with existing changes, may need permission from Merton Council. We assess your house honestly and tell you which route applies before you commit.
Because 40% of Mitcham homes are terraced and many others are semis, most extensions involve building up to or near the boundary, so party wall notices usually apply; you serve them as building owner, with the drawings and programme we supply. Separately, the structural and building fabric work is signed off under building regulations by building control. We coordinate the engineer's drawings and the inspections so the two processes run in parallel rather than tripping each other up.
Double storey extensions in Mitcham
Under permitted development a two-storey rear extension can go no more than 3 metres beyond the original rear wall and must stay at least 7 metres from the rear boundary, and in a conservation area it is not permitted development at all. Many gardens are too short for the 7 metre rule, so a double storey extension in Mitcham often needs planning permission from Merton Council. On the 40% of homes that are terraced, the neighbours' windows usually decide the depth. Merton's appraisal describes Mitcham Cricket Green as one of 28 designated conservation areas in the borough, designated as a conservation area in 1968 (council source). Our double storey extension page explains the build, at £1,800 to £2,600 per m² across both floors.
- Roof works and structural alterations at roof level
- First fix and second fix plumbing and electrics throughout
- Brickwork and mortar matched to the existing elevation
VOA Council Tax stock of properties, March 2025, for Mitcham East, Mitcham West and Mitcham South. Counts rounded by the VOA.
Why Choose GS Renovation in Mitcham
Homeowners in CR4 choose GS Renovation because we build extensions that respect the house they join onto, and we are straight about whether you need planning permission or can proceed under permitted development. If you are pairing a rear extension with a full refurbishment of the rest of the house, one programme covers both. One accountable team covers foundations, steel, roof and fit-out, with building control's inspections booked and managed by us, backed by our founder's 30+ years on the tools.
- Building control inspected at foundation, damp course and steel stages
- Foundation depth set after trial holes, drains and trees are checked
- Honest updates if a date or a detail has to move
Built a new extension at rear of property. Laid foundations, drainage, raised floor, new roof and completed all fixtures and interior decoration…
George was brilliant. Lovely bloke, very reasonably priced and a perfectionist to boot. He completed our small kitchen renovation with care and great…
George always kept to commitments and arrived on time. He offered helpful suggestions during his initial visit and promptly provided a reasonably…
FAQ
Frequently Asked Questions about House Extensions Mitcham
Are there hidden costs with house extensions in Mitcham?
Every extra cost on house extensions in Mitcham needs your written agreement, and the foreseeable ones are already priced within £2,000 to £2,800 per m² for a rear extension (indicative). Work in post-war suburban housing around CR4 occasionally reveals something behind plaster; when it does, GS Renovation stops, costs it and waits for your decision. The sequence of work stays fixed: the planning route is confirmed before drawings, and footings inspected before concrete.
Will my Mitcham rear extension need planning permission or is it permitted development?
It depends on the size and your property's history. Many single-storey rear extensions on Mitcham houses are permitted development, but larger, wrap-around or double-storey schemes often need a planning application to Merton Council. Either way, the structural work is signed off under building regulations, and a shared boundary usually means a party wall notice. We confirm the correct route before any work starts.
How close can a Mitcham extension be built to a tree?
It can be close, but trees change the foundation depth. Roots draw water from the ground, and on shrinkable soil that can move shallow footings, so the foundations are dug deeper or designed differently near trees. The building control inspector sees the trench before concrete goes in and may ask for more depth.
What does building control check during a Mitcham extension build?
Stages, not just the end. The first visit is at excavation, before the concrete, then drainage, the damp-proof course, the steel and insulation before they are covered, and a final visit for the completion certificate. Part L insulation standards apply to every new wall, floor and roof.
Can we stay at home while a Mitcham rear extension is built?
Most families do, because the new structure is built and weathered outside while the old rear wall still stands. The disruption peaks when that wall is opened and steel goes in, and when the kitchen is joined to the new space. Planning a temporary kitchen for those weeks makes it manageable.
How do we get daylight into the middle of a Mitcham extended house?
A deep rear extension can leave the original middle room dark, so rooflights or a lantern over the join are common. The glazing area affects the Part L calculation, because glass loses more heat than an insulated roof, so the rooflight sizes are fixed at design stage rather than added later.
Will a large Mitcham extension be liable for the Community Infrastructure Levy?
Only above a threshold. In Merton, a permission for any new dwelling or at least 100 square metres of new-build gross internal area will usually become liable for CIL. A single storey rear extension on a Mitcham house is normally far smaller. A large wrap-around combined with a two storey addition can approach it, and Merton's effective CIL residential rate for Mitcham, Morden and West Barnes is higher than its original rate, so check the gross internal area early.
Which Merton inspections should a Mitcham extension programme leave room for?
Merton's example inspection stages for an extension include excavation for foundations, oversite, and new walls with below ground drainpipes. Each is a hold point where work waits until the inspector has seen it. On a Mitcham extension, keep the trench open and the concrete lorry unbooked until the excavation visit is done, because the inspector or the structural engineer may ask for more depth once the ground is exposed.
How long does a Merton fast track decision take for a Mitcham extension?
Merton's fast track householder decision is up to 30 days from validation outside a conservation area and up to 46 days inside one. The clock runs from validation, not from submission, so a missing drawing or unpaid fee delays the start. For a Mitcham extension in the Cricket Green conservation area, plan on the longer window and order nothing with a long lead time until the decision arrives.
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