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.
Brent overview
House Extensions in Brent
Home to the Wembley regeneration zone, with steady demand for property refurbishment and repairs across a mixed housing stock. Brent falls well within the 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 Brent, that local knowledge means fewer surprises once work is on site and a team that already understands the borough's typical property stock.
Brent's housing stock reflects its position as an outer West London borough that grew rapidly through the interwar period. Much of the borough is characterised by 1920s and 1930s semi-detached and terraced housing, built as London's suburbs expanded along the underground and mainline rail routes. Alongside this are pockets of earlier Victorian and Edwardian terraces closer to the borough's older centres, purpose-built mansion blocks and low-rise flats from the mid-20th century, and post-war council estates of varying scale and condition. More recently, the Wembley regeneration zone has brought a wave of new-build apartment blocks and mixed-use developments into the borough, sitting alongside the older housing rather than replacing it wholesale. This mix means Brent's properties span a wide range of construction methods and ages, from solid brick interwar semis needing damp, roofing or extension work, to newer flats where refurbishment tends to focus on interior fit-out and maintenance. For a contractor, this variety means jobs in Brent rarely follow a single template, and each property's age and construction type shapes the approach needed.
The Wembley regeneration zone has kept construction activity in Brent fairly constant, and that wider building boom tends to spill over into steady demand for refurbishment and repair work on existing homes nearby. Owners of older properties often want to bring their homes up to a similar standard as the new developments going in locally, whether that's a kitchen or bathroom refurbishment, re-roofing, or general repair work following years of deferred maintenance. Landlords in particular face pressure to keep older flats and houses competitive as newer rental stock comes onto the market through regeneration, which pushes many towards refurbishing rather than leaving units untouched between tenancies. Because Brent's housing stock is so mixed, demand isn't concentrated in one type of job: some homeowners need small repair work, others need larger structural or extension projects. This variety, combined with steady background demand from regeneration-driven activity, means there's consistent but not overwhelming work across the borough, without any single dominant type of renovation project standing out.
Typical house extensions prices in London
Item
Typical 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.
How Long a London Extension Takes, Start to Finish
From first site visit to final sign-off, the pre-construction phase - the measured survey, design, structural engineering, deciding the planning route, the Building Control submission and any Party Wall Act notice period - commonly takes in the region of 2-4 months before groundworks even start, and this is where projects most often get compressed unrealistically in initial planning. Once on site, a straightforward single-storey rear extension under permitted development with a Building Notice typically runs somewhere around 12-16 weeks as a planning guide, once the design is settled and the structural engineer's calculations are in hand, though exact timing depends on your specific design and site conditions. A side-return or wraparound extension on a terrace usually adds a further 2-4 weeks to that build programme because of the underpinning work to the party wall foundation and the narrower access for materials and skips. A two-storey extension typically runs longer again, in the region of 16-22 weeks on site, because of the additional floor structure, the roof tie-in at first-floor level, and doubled first and second fix. None of these figures include a full planning application if one's needed, which can add roughly 8 weeks or more before groundworks start - and the Party Wall Act's two-month notice period (one month for adjacent excavation) runs in parallel with design and Building Control preparation where it's handled properly, instead of being tacked on afterwards. Served at the same time as your Building Control application it costs you no extra time overall, but served late, or if a neighbour appoints their own surveyor and negotiations drag, it can add real weeks to a job that's otherwise ready to start. Weather affects roofing and groundworks stages more than any other phase, which is why we sequence those for drier months where the programme allows it.
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.
Structural engineer sizes every steel beam and padstone before we price the job, catching problems Building Control would otherwise reject laterOne team runs the structural engineer, Building Control application and Party Wall Act 1996 process together rather than as three separate chasesWe advise Full Plans versus Building Notice based on your specific job's risk, not a default answerRegular coverage of Brent and the wider West London area
Signs to look for
Do you need house extensions in Brent?
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
A growing or multi-generational household needs an extra bedroom or bathroom that a two-storey extension could add above a ground-floor extension
How the work is handled in Brent
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
Step 2Design and route decision - permitted development, Larger Home Extension Scheme prior approval, or full planning permission
Step 3Structural engineer appointed to size steel beams, padstones and foundations and produce calculations for Building Control
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
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
Step 6CCTV drainage survey and, where needed, a build-over agreement application to the water company before foundations are dug
Step 7Groundworks - trial pits, foundation excavation and pour sized to the actual ground conditions and agreed depth
Step 8Structural steel installed and the opening formed between the existing house and new extension, with temporary propping as needed
Step 9Superstructure built with particular attention to insulation continuity at the wall-to-roof and wall-to-existing-house junctions
Step 10Windows, doors and roof glazing fitted to current Part L standards, followed by first-fix electrics and plumbing
Step 11Building Control inspections at foundations, DPC/membrane, drainage and insulation stages, through to completion certificate
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 Brent
How quickly can Lian start rear, side-return, wraparound and two-storey house extensions with structural engineering and Party Wall compliance in Brent?
Brent is part of our regular 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 Brent?
Yes. Brent falls within the area Lian Construction serves across Greater London.
My house is a 1930s semi - does that make refurbishment work more complicated?
Not necessarily, but it's worth knowing what you're dealing with before work starts. Interwar semis are generally solid, well-built properties, though issues like ageing wiring, older roofing materials or solid wall construction can affect how certain jobs are approached, particularly insulation or damp treatment. We'd normally want to look at the specific property first rather than assume, since condition varies a lot even among houses of the same age and design.
Why use Lian Construction rather than separate trades?
Lian Construction acts as a single accountable contractor for the whole extension, coordinating the structural engineer, the Building Control submission, and - where needed - the Party Wall surveyor as one sequenced process rather than you separately chasing three professionals who aren't talking to each other. We build extensions across London and into the surrounding Home Counties, and currently hold 26 five-star reviews on our Google Business Profile, built through completed jobs and organic word of mouth rather than paid advertising.
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.
Talk to Lian Construction about Brent
Send the site address in Brent, photos if available, and the house extensions work you need. We can review the scope and arrange the next step.