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Extensions & Structural Building Work in Southwark

House Extensions in Southwark, 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.

Southwark overview

House Extensions in Southwark

Active property market around Peckham and Bermondsey, with 800+ new council homes underway and strong buy-to-let refurbishment demand. Southwark falls well within the South 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 Southwark, that local knowledge means fewer surprises once work is on site and a team that already understands the borough's typical property stock.

Housing stock in Southwark spans several distinct eras. Peckham and the surrounding streets have a good deal of Victorian and Edwardian terraced housing, typical of inner London's rapid nineteenth-century expansion, alongside interwar and postwar low-rise estates. Bermondsey, given its history as a working wharf and warehouse district, has a mix of converted industrial buildings sitting alongside traditional terraces and mid-rise blocks, a pattern common in London's former riverside industrial areas. With 800+ new council homes underway across the borough, there's also a growing share of newer build stock, which brings different maintenance and refurbishment needs than the Victorian terraces nearby, think modern insulation, service runs and warranty considerations rather than solid-wall damp and old timber. For homeowners and landlords, this mix means a wide range of jobs: period property repair and upgrade work on older terraces, conversion and refurbishment work on ex-industrial buildings, and fit-out or snagging work on newer stock. It's a borough where a contractor needs to be comfortable moving between very different building types and ages, sometimes on the same street.

Southwark's property market, particularly around Peckham and Bermondsey, has stayed active for some time, and that shows in the volume of refurbishment and improvement work landlords and owner-occupiers are commissioning. Buy-to-let refurbishment demand is strong: with rental interest firm in these areas, landlords are investing in kitchen and bathroom upgrades, rewiring and general modernisation to keep properties competitive and up to current letting standards. The 800+ new council homes underway across the borough also point to a wider building pipeline locally, which tends to pull more trades and subcontractor activity into the area generally, and can make it harder to get a reliable contractor booked in at short notice. For homeowners, this means it's worth planning refurbishment work with some lead time rather than expecting immediate availability, particularly for larger or structural jobs. For landlords managing multiple units, coordinating between-tenancy refurbishment efficiently matters more here than in quieter markets, since void periods are costly and good contractors are being pulled in several directions by both private and public sector work at once.

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.

Permitted Development or Full Planning Permission

Most single-storey rear extensions in London fall under the Town and Country Planning (General Permitted Development) (England) Order 2015, which allows a rear extension up to 3m deep for a terraced or semi-detached house, or 4m for a detached house, without a full planning application, subject to height and eaves limits. Go beyond that, up to 6m for a terrace/semi or 8m for a detached house, and you need prior approval under the Larger Home Extension Scheme, which runs as a lighter-touch neighbour consultation process through the council rather than a full application, with a statutory determination period of around six weeks. Side extensions have tighter limits under permitted development, generally single-storey and no wider than half the original house width, which is why most side-return jobs on terraces get combined into a full planning application alongside the rear element instead of trying to split the two. Conservation areas, and Article 4 Directions that specific boroughs apply on top of them, can remove permitted development rights for extensions entirely, meaning even a modest single-storey rear addition needs a full application with an 8-week (or longer, for larger schemes) decision timeline. We check this at the first site visit against your specific borough's local plan and any conservation area or Article 4 status before pricing, because the planning route affects the programme more than the build itself does.

Building Control: Full Plans or Building Notice

Separately from planning permission, every extension needs Building Control sign-off under the Building Regulations 2010, and there are two routes to get it: a Full Plans application, where detailed drawings and structural calculations are submitted and formally approved before work starts, typically taking 5-8 weeks; or a Building Notice, where you can start on site as little as 2 days after submission but without prior approval of the design, meaning any problems get picked up on site inspections instead of on paper beforehand. For a straightforward single-storey rear extension with a well-understood structural opening, a Building Notice can be the faster, lower-friction route. For anything with more structural or ground-condition risk - a side-return with underpinning, a two-storey addition, unusual soil conditions, or a design close to the boundary - we generally recommend Full Plans, because getting the steel sizing and foundation design checked and approved before you dig avoids a stop-work order mid-excavation if Building Control isn't satisfied. Part A covers structural stability, Part L sets the thermal performance targets for the new walls, roof, windows and doors and caps how much of the extension's floor area can be glazed, and Part H4 requires water company approval for any foundation within 3m of a public sewer. We decide the route with you at the design stage based on the specific job, not as a default answer.

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 Southwark and the wider South London area

Signs to look for

Do you need house extensions in Southwark?

  • 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
  • You're relying on a side-return, alley or awkward rear garden as dead storage space rather than usable floor area

How the work is handled in Southwark

  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 Southwark

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

Southwark is part of our regular South 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 Southwark?

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

Is it worth doing a full refurbishment between tenants for a buy-to-let in Southwark?

It depends on the property's condition and how competitive the local rental market is for that type of unit, but with buy-to-let refurbishment demand strong in this area, a fair number of landlords choose to update kitchens, bathrooms and decor between tenancies to justify rent levels and reduce void periods. Whether it's worth it for you comes down to the numbers: cost of works against expected rent uplift and reduced vacancy. A contractor can give you a realistic cost for the works, but the rental strategy side is worth thinking through separately.

How long does a house extension take, start to finish?

The pre-construction phase - survey, design, structural engineering, deciding the planning route, Building Control submission and the Party Wall notice period - commonly takes in the region of 2-4 months before groundworks even start. Once on site, a straightforward single-storey rear extension typically runs around 12-16 weeks as a planning guide, a side-return or wraparound usually adds a further 2-4 weeks for underpinning and narrower material access, and a two-storey extension typically runs longer again, around 16-22 weeks, because of the additional floor structure and roof tie-in. None of this includes a full planning application if one's needed (roughly 8 weeks or more) - we run the Party Wall notice period in parallel with design and Building Control preparation rather than tacking it on afterwards, which is what keeps the programme realistic. Exact timing always depends on your specific design and site conditions.

Is a two-storey extension cheaper per square metre than a single-storey one?

Often, yes - a two-storey side or rear extension typically costs roughly £2,800-£4,200/m², lower than a single-storey extension's £3,000-£5,000/m², because the foundation and roof, the two most expensive elements of any extension, are shared across double the floor area. Total project cost is still higher overall, commonly £120,000-£200,000+, but the cost per square metre of usable space is generally better value.

Do I need a structural engineer for my extension?

Yes, for any load-bearing opening or new foundation - a structural engineer sizes the steel beam or RSJ, specifies padstones and bearings, and designs the foundation to suit your ground conditions, producing the calculations Building Control requires for sign-off. Pricing a job off a guessed beam size instead of a calculated one is one of the most common reasons a knock-through opening gets rejected once Building Control inspects it, which then costs time and money to correct mid-build.

Talk to Lian Construction about Southwark

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

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