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Extensions & Structural Building Work in Richmond upon Thames

House Extensions in Richmond upon Thames, 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.

Richmond upon Thames overview

House Extensions in Richmond upon Thames

Neighbouring Kingston, with a similar stock of period and riverside properties suited to full refurbishment and roof replacement work. Richmond upon Thames falls well within the South West 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 Richmond upon Thames, that local knowledge means fewer surprises once work is on site and a team that already understands the borough's typical property stock.

Richmond upon Thames sits alongside Kingston and shares a similar mix of period and riverside properties. Expect a good number of Victorian and Edwardian terraces and villas, along with detached and semi-detached houses from the interwar years, many with later extensions and loft conversions added over time. Riverside stretches bring their own building types, older properties close to the water that were built before modern damp-proofing standards, along with some larger detached houses on wider plots. As with much of outer London, roofs on this older stock tend to be slate or clay tile, often original or close to it, with the valleys, flashings, and chimneys typically the first parts to need attention. Loft space is often tight in these properties, which makes roofline work and extensions a common route for adding usable space rather than moving house. This combination of age, riverside exposure, and a general preference among owners to extend and upgrade rather than relocate is what tends to drive demand for full refurbishment and roof replacement work in this part of south west London.

Given the age and type of housing stock, roof replacement and full refurbishment work tend to be steady sources of demand in Richmond upon Thames, much as they are in neighbouring Kingston. Owners of period and riverside properties are often dealing with roofs and structural elements that are decades past their original install, so replacement or significant repair becomes a practical necessity rather than a cosmetic choice. Riverside proximity can also mean a closer eye needed on damp and moisture-related issues, which often surface alongside roofing problems and get picked up during a wider refurbishment. Because this is an area where owners tend to invest in upgrading rather than moving, full refurbishment projects, spanning roofing, structural work, and internal modernisation, are a natural fit for the type of property found here. For a homeowner or landlord, this generally means budgeting for work that addresses the building as a whole rather than a single room, and choosing a contractor comfortable working on older properties where standard modern assumptions about structure, insulation, or roof pitch may not apply. Landlords with older buy-to-let stock in particular tend to prioritise roof condition, since it affects both letting standards and long-term maintenance costs.

With period property forming a significant part of the housing stock in this part of south west London, conservation area status and, in some cases, listed building designation are worth checking before starting work. Many outer London boroughs have conservation areas covering older residential streets, and these can affect what materials and roof profiles are acceptable, along with rules around extensions, dormers, and changes to the front of a property. Riverside locations sometimes carry additional planning considerations too. None of this means work cannot go ahead, but it usually means a bit more upfront checking with the local council before committing to a design or materials choice. As a general rule, it is worth confirming conservation area or listed status early, since it shapes what a roof replacement or extension can look like and how long approval might take.

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 Richmond upon Thames and the wider South West London area

Signs to look for

Do you need house extensions in Richmond upon Thames?

  • 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
  • You've outgrown a two- or three-bed Victorian/Edwardian terrace or ex-council flat, but moving in Zone 2-4 London would cost more in stamp duty and fees than extending the current property

How the work is handled in Richmond upon Thames

  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 Richmond upon Thames

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

Richmond upon Thames is part of our regular South West 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 Richmond upon Thames?

Yes. Richmond upon Thames falls within the area Lian Construction serves across Greater London.

Can you match the original roof materials on an older property?

In most cases, yes, though it depends on what the existing roof is made of and whether matching materials are still readily available. Slate and clay tile are common on period properties in this area, and reclaimed or close-match materials are usually possible to source. If the property is in a conservation area, matching the original appearance is often expected by the council anyway, so we would factor that into the specification from the outset.

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 Richmond upon Thames

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

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