House Extensions in Hillingdon, 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.

Hillingdon overview

House Extensions in Hillingdon

West London borough near Heathrow, with a broad mix of housing types needing refurbishment and general building work. Hillingdon 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 Hillingdon, that local knowledge means fewer surprises once work is on site and a team that already understands the borough's typical property stock.

Hillingdon's housing stock reflects its position as an outer west London borough that grew substantially through the interwar and postwar periods, alongside older cores around its traditional town centres. Expect a broad spread: 1930s semi-detached and terraced housing built as London's suburbs expanded along the western rail and tube corridors, postwar estates and infill from the 1950s-60s, and pockets of older Victorian and Edwardian terraces closer to the historic centres. More recent decades have added modern estate housing and some higher-density new-build, partly linked to the borough's role as a major employment and transport hub near Heathrow. This mix means refurbishment work varies widely in character: solid-wall older properties often need different approaches to insulation, damp and roofing than cavity-wall postwar housing, and newer stock brings its own snagging and extension challenges. A contractor working across Hillingdon needs to be comfortable moving between these eras rather than specialising in one type, since a single street can contain anything from a 1930s semi to a 1990s infill house.

Hillingdon's location next to Heathrow shapes demand in practical ways. A large share of housing serves a working population tied to the airport and surrounding logistics and business parks, which tends to mean higher churn in the private rental sector and steady demand for quick, reliable turnaround work between tenancies: redecoration, repairs, kitchen and bathroom refreshes, and general maintenance that keeps a property lettable. Landlords in this position usually want a contractor who can scope a job fast and work to a clear timeline, since void periods cost money. At the same time, the borough's broad mix of housing types means demand for larger projects - extensions, loft conversions, roofing - comes from owner-occupiers across very different property styles, not a single dominant demographic. Because Hillingdon sits toward the edge of a typical London contractor's usual coverage area, homeowners here can sometimes find it harder to get firms to travel out for smaller jobs, or face longer lead times than in more central boroughs. That gap tends to favour contractors willing to commit to the area consistently rather than treat it as an occasional job.

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.

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 Hillingdon and the wider West London area

Signs to look for

Do you need house extensions in Hillingdon?

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 Hillingdon

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 Hillingdon

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

Hillingdon 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 Hillingdon?

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

My house is a 1930s semi - what kind of issues should I expect during refurbishment?

Interwar semis are common across Hillingdon and generally have decent bones, but you'll often find things like ageing single-skin extensions, outdated wiring or plumbing runs, and roofs that are due for attention if they haven't been touched in a while. Cavity walls from this era can also have insulation gaps. We'd usually want to have a look in person before saying anything more specific, since condition varies a lot even on the same street.

Do I need to serve Party Wall Act notices for a house extension?

If your extension involves work on a shared party wall, or excavation within 3m or 6m of a neighbour's foundation depending on depth, yes - the Party Wall etc. Act 1996 requires two months' notice for wall work or one month for adjacent excavation. If a neighbour dissents or doesn't respond, a schedule of condition survey and a formal Award are needed; party wall surveyor cost in London typically runs £900-£2,000 through one agreed surveyor or £2,000-£3,000+ if each side appoints separately, borne by you as the building owner. Starting groundworks before that notice period has run, or without an Award where required, exposes you to an injunction that can stop the job entirely - this applies to the large majority of terrace and semi-detached extensions in London.

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.

Talk to Lian Construction about Hillingdon

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

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