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Extensions & Structural Building Work in Greenwich

House Extensions in Greenwich, London

Extending a Victorian terrace, Edwardian semi or ex-council maisonette means forming a new structural opening into a house that predates modern Building Regulations. We handle the structural engineer, Building Control route and Party Wall Act 1996 process together, from rear and side-return extensions through to full two-storey additions.

Greenwich overview

House Extensions in Greenwich

A large stock of Victorian and Edwardian houses with essentially no dedicated roofing competitor coverage. Greenwich falls well within the South East London ground Lian Construction covers on a regular basis. For rear, side-return, wraparound and two-storey house extensions with structural engineering and Party Wall compliance in Greenwich, that local knowledge means fewer surprises once work is on site and a team that already understands the borough's typical property stock.

Greenwich has a large stock of Victorian and Edwardian houses, much of it terraced or semi-detached, built in the decades either side of 1900 as London's suburbs expanded along the riverside and rail lines. As with similar housing across inner and near-inner London boroughs, roofs on these properties are typically slate or clay tile, often with parapet walls, valley gutters, and multiple original chimney stacks. Many houses will have had partial re-roofing, loft conversions, or rear extensions at some point over the past century, which means roof coverings and detailing are frequently mixed ages even on a single property. Bay windows with their own small roofs, and shared or party-wall guttering between terraced neighbours, are common features that need particular care during repair work. Given the age of this housing stock, issues such as slipped or missing tiles, ageing lead flashing around chimneys, and worn valley gutters are the kind of thing homeowners in Greenwich are likely to encounter periodically, rather than one-off problems. Property condition varies a good deal street by street depending on maintenance history, so what one house needs can differ significantly from its neighbour.

With a large stock of Victorian and Edwardian houses and essentially no dedicated roofing competitor coverage in the area, homeowners and landlords in Greenwich are often left choosing between general builders who treat roofing as a sideline, or firms based further afield who may not prioritise smaller local jobs. This gap tends to show up most clearly with urgent repairs, where a slipped tile or a leak after a storm needs someone who can attend quickly rather than fit the job in around larger contracts elsewhere. It also affects planning and quoting for larger work such as full re-roofs or chimney repairs, where a lack of specialist local knowledge can mean longer lead times or less accurate initial assessments. For landlords managing older rental stock, this matters because roof issues left unresolved tend to escalate into damp and interior damage, which is more disruptive and costly to fix than catching problems early. Homeowners undertaking wider refurbishment work, such as loft conversions or extensions, may also find it harder to coordinate roofing specifically as part of a bigger project if there isn't a contractor locally who covers that trade in depth. In practice, this means demand for reliable, responsive roofing and refurbishment work in Greenwich likely outstrips the readily available supply.

Given the concentration of Victorian and Edwardian houses in Greenwich, conservation area and, in some cases, listed building considerations are worth checking before starting roofing or exterior refurbishment work. As in many outer and inner London boroughs with older housing stock, parts of Greenwich may fall within conservation areas, where changes visible from the street, such as replacing roof coverings with a different material, altering rooflines, or adding roof windows to a front elevation, can require planning permission even where similar work elsewhere would be permitted development. Chimney stacks and original architectural detailing are often specifically protected in these areas. It's worth checking with the local planning department or a surveyor early on, since retrospective permission is harder to secure than getting it sorted before work starts. This doesn't apply to every property, and plenty of routine repairs and like-for-like replacements fall outside these controls, but it's a sensible thing to verify given the age of the housing stock.

Typical house extensions prices in London
ItemTypical range
Single-storey rear extension (per m²)£3,000–£5,000
Side-return / wraparound extension (per m²)£4,500–£5,500
Two-storey extension (per m²)£2,800–£4,200
Structural opening / RSJ steel beam£1,800–£4,500+

General London market guidance, not a fixed quote — actual pricing depends on a site survey. Full breakdown: cost guide.

Where Extensions Go Wrong After Handover

The two most common defects we see on extensions built by other firms both show up well after handover, which is what makes them expensive to fix. The first is cold bridging at the junction where the new extension's roof or wall meets the original house - most often where a steel lintel or beam crosses a masonry wall, or at the wall-to-roof and wall-to-floor abutments - which doesn't show up until the first or second winter, when it appears as a stripe of mould or condensation tracking along the junction because insulation continuity wasn't maintained through the detail. We check and photograph this junction detailing at framing stage, before it's boarded over and impossible to verify. The second is a bridged damp-proof course, where the new extension's floor slab, external render, or a raised patio built up against the original wall isn't lapped correctly with the existing DPC, or ends up above the 150mm minimum clearance below it, so damp tracks up the original wall internally regardless of how well the rest of the extension is built. Other recurring issues include undersized foundations on London clay where a trial pit wasn't dug before pricing, steel beams sized by guesswork instead of calculation - one of the most common Building Control rejection points on knock-through openings - drainage clashes where an existing combined or shared drain runs under the proposed footprint and wasn't surveyed first, and poor flashing at the roof tie-in on side-return and wraparound jobs, which shows up as a leak the first time it rains hard.

Drainage Surveys and Build-Over Agreements with Thames Water

A detail that catches a lot of homeowners out mid-project: if your proposed extension footprint sits within 3m of a public sewer, or within 1m of a public lateral drain, Building Regulations Part H4 requires formal approval from the water company - a build-over agreement, usually with Thames Water in London - before foundations can be dug, on top of and separate from your Building Control approval. Many Victorian and Edwardian terraces have combined drains running under the rear garden roughly where a rear extension footprint naturally falls, sometimes shared with the neighbouring property, and the exact route often isn't obvious from the surface. We commission a CCTV drain survey at the design stage specifically to catch this before foundations are priced, because discovering a drain run under your footprint once excavation has started means redesigning the foundation, diverting the drain, or repositioning the extension - all of which cost far more mid-dig than they would have on paper. A build-over agreement application typically adds a few weeks to the pre-construction programme, which is manageable if it's planned in from the start alongside the Party Wall notice period and Building Control application, but becomes a genuine hold-up if it's only discovered once the trial pit is already open.

Structural engineer sizes every steel beam and padstone before we price the job, catching problems Building Control would otherwise reject later
One team runs the structural engineer, Building Control application and Party Wall Act 1996 process together rather than as three separate chases
We advise Full Plans versus Building Notice based on your specific job's risk, not a default answer
Regular coverage of Greenwich and the wider South East London area

Signs to look for

Do you need house extensions in Greenwich?

  • You've had conflicting advice about whether your project needs full planning permission, prior approval, or falls under permitted development, and nobody's checked your borough for an Article 4 Direction or conservation area status
  • A previous quote priced the job without mentioning a structural engineer, a soil or trial pit assessment, or a Party Wall Act process - on a terraced or semi-detached house that usually means the price is wrong or incomplete
  • There's visible evidence of a botched earlier extension on the property - a cold stripe of mould along a roof-to-wall junction, a damp patch where a patio's built up against the original wall - and you need it diagnosed and corrected as part of any new work
  • Your kitchen or living space is genuinely too small for how the household actually uses it day to day, not just cosmetically dated

How the work is handled in Greenwich

  1. Step 1Initial site visit and measured survey of the existing house, boundary lines, drainage runs and nearby trees, checked against permitted development limits and the borough's conservation area / Article 4 status
  2. Step 2Design and route decision - permitted development, Larger Home Extension Scheme prior approval, or full planning permission
  3. Step 3Structural engineer appointed to size steel beams, padstones and foundations and produce calculations for Building Control
  4. Step 4Building Control application submitted - Full Plans (formal approval in 5-8 weeks) or Building Notice (start in 2 days, no prior sign-off) - decided on the specific job's structural and ground-condition risk
  5. Step 5Party Wall etc. Act 1996 notices served on affected neighbours where a shared wall or nearby excavation applies, run in parallel with Building Control rather than after it
  6. Step 6CCTV drainage survey and, where needed, a build-over agreement application to the water company before foundations are dug
  7. Step 7Groundworks - trial pits, foundation excavation and pour sized to the actual ground conditions and agreed depth
  8. Step 8Structural steel installed and the opening formed between the existing house and new extension, with temporary propping as needed
  9. Step 9Superstructure built with particular attention to insulation continuity at the wall-to-roof and wall-to-existing-house junctions
  10. Step 10Windows, doors and roof glazing fitted to current Part L standards, followed by first-fix electrics and plumbing
  11. Step 11Building Control inspections at foundations, DPC/membrane, drainage and insulation stages, through to completion certificate
  12. Step 12Second fix, decoration and snagging, confirming the new damp-proof membrane is properly lapped with the original house's DPC before ground levels are finished

Questions

House Extensions questions in Greenwich

How quickly can Lian start rear, side-return, wraparound and two-storey house extensions with structural engineering and Party Wall compliance in Greenwich?

Greenwich is part of our regular South East London coverage, so once we've surveyed the property we can usually confirm a start date quickly. Send the address and scope and we'll arrange the next step.

Do you cover all of Greenwich?

Yes. Greenwich falls within the area Lian Construction serves across Greater London.

Why is it hard to find a roofer in Greenwich who isn't booked out for weeks?

Greenwich has a lot of older Victorian and Edwardian housing that needs regular roof maintenance, but there isn't much dedicated roofing coverage locally, so general builders and firms from further out end up covering the gap. That tends to push out lead times, especially for anything that isn't a genuine emergency. Booking ahead for planned work, rather than waiting until there's a leak, generally gets you a better slot and more time to plan the job properly.

How much does a house extension cost in London in 2026?

A single-storey rear or side extension typically costs £3,000-£5,000 per square metre all-in, including VAT, the structural engineer and Building Control fees, so an 18-20m² kitchen extension usually lands around £55,000-£95,000. Side-return and wraparound extensions on Victorian and Edwardian terraces run higher, roughly £4,500-£5,500/m², because of party wall underpinning, narrow rear access and longer steel spans. Two-storey extensions are often cheaper per square metre, around £2,800-£4,200/m², because the foundation and roof cost is shared across two floors, though total project cost is usually higher in absolute terms, commonly £120,000-£200,000+.

Do I need planning permission for a house extension in London?

Not necessarily - a single-storey rear extension up to 3m deep (terrace/semi) or 4m (detached) generally falls under permitted development, and up to 6m/8m via the Larger Home Extension Scheme prior approval route, a lighter-touch neighbour notification through the council rather than a full application. But conservation area status or an Article 4 Direction, both common across London boroughs, can remove permitted development rights entirely, meaning even a modest extension needs a full planning application with an 8-week (or longer, for larger schemes) decision timeline - we check this against your borough's specific status at the first site visit.

What is the Larger Home Extension Scheme?

It's the prior approval route under permitted development that lets a single-storey rear extension go beyond the normal 3m/4m depth limit, up to 6m for a terraced or semi-detached house or 8m for a detached house. Rather than a full planning application, the council runs a lighter-touch neighbour consultation and issues a decision, with a statutory determination period of around six weeks. It still isn't available everywhere - conservation areas and Article 4 Directions can remove the right to use it, in which case a full planning application is the only route regardless of the extension's depth.

Talk to Lian Construction about Greenwich

Send the site address in Greenwich, photos if available, and the house extensions work you need. We can review the scope and arrange the next step.

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