House Extensions Eltham
Single storey rear and double storey extensions in Eltham, 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 Eltham to your designer's approved drawings, where 1930s semi-detached and interwar houses sit on the generous plots that make expansion possible. We handle foundations, steelwork, roofing and the full fit-out as one accountable project.
In Eltham, 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 Eltham: 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 Eltham
Eltham range: choose above
Rear and side extensions on Eltham plots
The deeper gardens and wider side accesses common to Eltham's interwar houses lend themselves well to rear and side-return extensions. A single storey rear extension can turn a cramped kitchen into an open-plan kitchen-diner, while filling in the side passage widens the whole ground floor. We start with proper foundations and groundworks suited to the local soil, then bring in steel beams where the original external wall is opened up into the new space. Whether it is a kitchen extension or a single room extension for a playroom or study, the same permitted development and building control rules apply.
Double storey and wrap-around extensions add bedrooms and en-suites above the new ground floor, making the most of these family homes without moving out of the area. We manage the roof works, whether a pitched roof to match the existing house or a flat roof to a rear projection, and carry the project through to a finished, decorated interior with kitchen, bathroom and services all in place.
Housing in Eltham
Eltham counts roughly 14,360 homes for Council Tax; 17% are older than 1919, 52% interwar and 30% post-war, with 27% flats and 73% houses. 35% of homes here are semi-detached; a rear extension on a semi in Eltham digs beside the attached neighbour, so one party wall notice is usual.
Conservation areas, first floors and trees on an Eltham extension
Royal Greenwich's Urban Design Guide says first-floor rear extensions are not classed as permitted development in conservation areas. Eltham Palace Conservation Area was designated in 1971 and Eltham Green Conservation Area in 1975, and the council's list of its conservation areas shows which are under Article 4 directions. If your house sits inside either, a two storey rear extension goes to a planning application from the start, so the programme carries the planning period before any building work begins. A single storey rear extension can still be permitted development there unless an Article 4 direction removes it, but a side extension cannot. Find the boundary on the conservation area map before the designer draws anything, not after.
Trees are the other early check. In Royal Greenwich conservation areas you must give six weeks written notice for work to, or felling of, trees more than 75mm in diameter. A tree near the footprint of an Eltham extension may need roots cut back for the trench or its crown lifted for the scaffold, and both can count as work to the tree. Six weeks is longer than people allow, so the notice goes in alongside the planning application, not when the digger arrives. The structural engineer we appoint also needs the species and distance of that tree to set the foundation depth.
Planning and party walls in SE9 extensions
Whether your Eltham extension is permitted development or needs a full planning application depends on the property, its size and what has been built before. Many single storey rear extensions on interwar semis fall under permitted development, but larger projects, work to the front, or anything affecting the street scene may need permission from the Royal Borough of Greenwich. Many of the Arts and Crafts cottages around Well Hall Pleasaunce sit within a conservation area, where side extensions and two storey rear extensions need planning permission, so check the address first. We advise honestly on which route applies to your SE9 home before any drawings are finalised.
Because Eltham semis usually share a party wall, extending near that boundary or building on a shared foundation brings the Party Wall Act into play, and you must serve notice on your neighbour (or your surveyor does). Separately, the structural work itself, including the steel beams and new foundations, is controlled under building regulations and inspected by building control. We keep planning, party wall and building regs matters clearly separate and properly handled.
Kitchen extensions in Eltham
53% of the houses in Eltham are semi-detached or detached, which usually leaves room for a kitchen extension across the full rear width, with a steel beam over the opening into the house. The fit-out is priced on its own page, kitchen renovation in Eltham; the build figures are in the table above.
Double storey extensions in Eltham
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 Eltham often needs planning permission from the Royal Borough of Greenwich. With 39% of homes here semi-detached or detached, the side of the house is often an option too. Eltham Palace Conservation Area was designated in 1971 and its character appraisal was adopted in January 2008 (council source). Our double storey extension page explains the build, at £1,800 to £2,600 per m² across both floors.
- Full fit-out, finishing and making good
- Roof works and structural alterations at roof level
- Steel goalpost frames where the rear wall opens up
VOA Council Tax stock of properties, March 2025, for all 5 statistical areas in Eltham. Counts rounded by the VOA.
Why Eltham Homeowners Choose GS Renovation
Eltham families choose GS Renovation because we build extensions that suit the interwar house, not a generic box. One team handles groundworks, steel, roofing and fit-out, advises whether you need planning or fall under permitted development, and programmes the work around the party wall notices you serve on neighbours. Backed by our founder's 30+ years on the tools, we deliver space you can actually use.
- Building control inspected at foundation, damp course and steel stages
- Foundation depth set after trial holes, drains and trees are checked
- A written scope and programme agreed before work starts
Built a new extension at rear of property. Laid foundations, drainage, raised floor, new roof and completed all fixtures and interior decoration…
Giorgio is an excellent and intelligent workman, and with very reasonable prices! He installed a kitchen extractor fan in a complicated situation…
George was brilliant. Lovely bloke, very reasonably priced and a perfectionist to boot. He completed our small kitchen renovation with care and great…
FAQ
Frequently Asked Questions about House Extensions Eltham
What does the house extensions quotation for an Eltham home cover?
Labour, materials, approvals, reinstatement and the programme are all on the house extensions quotation for an SE9 home in Eltham, inside £2,000 to £2,800 per m² for a rear extension (indicative). GS Renovation writes it so each element can be checked against another builder's round number. The scope reflects the property, because the depth of neighbouring Eltham foundations decides how deep the new footings go. Email info@gsrenovationltd.co.uk to see a sample layout.
Will my Eltham rear extension need planning permission or is it permitted development?
It depends on the size and your specific house. Many modest single storey rear extensions on Eltham's interwar semis qualify as permitted development, but larger or two storey projects, or work facing the street, often need a planning application to the Royal Borough of Greenwich, as do side extensions on a house in a conservation area, such as the cottages around Well Hall Pleasaunce. We assess your SE9 property early and tell you clearly which route applies before committing to a design.
Does digging foundations for an Eltham extension need a party wall notice?
It can, even if you build entirely on your own land. On an attached Eltham semi, a rear extension trench usually runs within 3 metres of next door and deeper than their old footings, and that combination obliges you to give the adjoining owner a month's warning in writing. Building on or astride the boundary line needs notice as well. Serve it early, because a dissent means appointing surveyors before any digging starts.
What if a drain runs under the footprint of my planned Eltham extension?
Find out before the design is fixed. A camera survey shows whether it is your private drain or a shared public sewer. A private run can often be rerouted or bridged under Part H, with the falls kept. Building over or close to a public sewer needs consent from the water company, and that can move the extension line or change the foundation design.
How do the soil and garden trees affect extension foundations in Eltham?
They can decide the depth. Eltham sits partly on clay subsoil, which shrinks and swells as trees draw moisture out of it, so the engineer checks nearby trees and hedges and may specify deeper trench-fill or a different foundation type. The building control inspector sees the excavation before any concrete is poured, and that visit can set the final depth.
Which building control inspections happen during an extension in Eltham?
Several, each at a point where the work is about to be covered. The foundation trench before concrete, drainage before backfilling, the damp-proof course and floor slab, then the steel where the house wall is opened up, and insulation before plastering, since the extension must meet current Part L standards. A final inspection leads to the completion certificate. Missing one can mean opening up finished work.
Does an Eltham extension near a public sewer need a full plans application?
Yes, if it is over the sewer or within three metres of it. Royal Greenwich requires full plans in that case, so the quicker notice route is closed to that extension. Behind an Eltham semi, the shared run collecting from neighbouring houses can pass close to the back wall. Open the manhole at the first visit and trace any unclear run before the design is fixed, so the route through building control is known early.
Can a residential extension in Eltham claim relief from the Community Infrastructure Levy?
Yes. Royal Greenwich lets self-build residential extensions and annexes claim relief from CIL using its published exemption forms. Its current charging schedule was adopted on 24 July 2024 and came into force on 26 July. Where an Eltham extension is large enough to be liable, the relief is claimed on the form before work starts on site, because relief claimed after commencement can be lost.
Does an Eltham extension need a Flood Risk Assessment?
Only where the address is in Flood Zone 2 or 3. Royal Greenwich requires a Flood Risk Assessment for all developments in Flood Zones 2 and 3, and it says in terms that this includes domestic extensions. Check the flood map for the address when the planning route is being decided. The assessment is part of the planning application, and its findings can set the floor level of the new room.
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