Types of House Extensions London: Which One Suits Your Property?
Six extension types, their London costs, their planning position, and which property each one suits so you can choose the right scheme before you commission a single drawing.
What are you renovating?
Most London homeowners know they want more space. Fewer know which type of extension will give them the most of it within their budget, within their planning constraints, and within the limits of what their property can structurally support.
The choice matters more than people expect. A single-storey rear extension on a Victorian terrace in Lewisham and a two-storey side extension on a Thirties semi in Ealing look nothing alike and cost very different amounts. Getting the type right before you commission an architect is the decision that shapes everything that follows.
This guide covers the six main types of house extensions built in London, what each costs, what planning permission each requires, and which property types they suit best.
A Project That Started with the Wrong Extension Type
When the owners of a mid-terrace Victorian house on Ulverscroft Road SE22 contacted us in early 2024, they had already spoken to an architect about a single-storey rear extension. The architect had drawn up a scheme extending five metres beyond the rear wall into the garden, which sat comfortably within Permitted Development limits. The quoted cost was £82,000.
A second architect suggested something different: a wraparound extension combining a modest rear extension with a side return infill. The side return, a narrow strip of land running alongside the ground floor left over from the original terraced layout, added barely 1.8 metres in width, but when folded into the rear extension, it created an L-shaped kitchen-diner 40% larger than the rear-only scheme, for a total of £97,000.
The extra £15,000 bought a room that worked. The rear-only scheme would have been long and narrow; the wraparound was wide enough for an island and a dining table. Three matched quotes confirmed the price, and work started in the spring.
The point is not that a wraparound is always better. It is that the type of extension determines the room you end up with, and the choice is worth making deliberately before any drawings are commissioned.
1. Single-Storey Rear Extension
What it is: An extension built out from the rear of the property at ground floor level, typically beneath a flat or slightly pitched roof. The most common extension type in London.
Typical size: 3–6 metres deep, the full width of the property or narrower.
Best for: Victorian and Edwardian terraces and semis, post-war houses, ground-floor flats with garden access (subject to lease).
What you get: A larger kitchen, kitchen-diner, or family room. The most popular use is an open-plan kitchen-diner-living space that connects to the garden via bifold or sliding doors.
Planning position: Under Permitted Development (PD), a detached house can extend up to 8 metres; a terrace or semi up to 6 metres under Prior Approval (Neighbour Consultation Scheme). Standard PD limits (without Prior Approval) are 4 metres for detached and 3 metres for terraces and semis. Properties in conservation areas, Article 4 Direction zones, or listed buildings may require full planning permission regardless of size.
Party wall: A rear extension on a mid-terrace property triggers the Party Wall etc. Act 1996 if it sits within 3 metres of an adjoining owner’s structure or if excavation goes below their foundations. Notices must be served before work begins.
Cost range (London): £50,000–£120,000 all-in, depending on size, specification, and whether structural changes are needed inside.
Two-Storey Rear Extension
What it is: A rear extension built on two floors, adding space at both ground and first floor level. The ground floor typically becomes kitchen-diner-living; the first floor adds a bedroom or bathroom.
Typical size: 3–6 metres deep, single or full width of the rear elevation.
Best for: Houses with two or more storeys, where additional bedroom or bathroom space is needed alongside a larger ground-floor room. Less common on terraces due to party wall and overlooking complications.
What you get: Ground-floor open-plan space plus an additional bedroom or en-suite above. Can transform a three-bedroom house into a four-bedroom without a loft conversion.
Planning position: Almost always requires full planning permission. The standard PD allowance for a two-storey extension is 3 metres beyond the rear wall, and the extension must not exceed the height of the original ridge. In practice, the restriction on overlooking neighbours means planning consent is usually needed even when the dimensions are within limits.
Party wall: Almost always applies. Two-storey extensions involve more complex notifications, particularly where the upper floor sits alongside or close to an adjoining property.
Cost range (London): £85,000–£180,000, depending on width, internal specification, and the structural complexity of adding a floor above.
Side Return Extension
What it is: An extension that fills in the narrow strip of land running alongside the ground floor of a Victorian or Edwardian terrace, the original space left between the house and the boundary fence. Typically one storey.
Typical size: 1.5–3 metres wide, the length of the existing ground floor (often 5–8 metres).
Best for: Victorian and Edwardian mid-terraces and end-terraces where the side return is an unused passageway. Common in inner London boroughs: Hackney, Islington, Lambeth, Southwark, Lewisham.
What you get: A wider kitchen or kitchen-diner at the rear of the house. The transformation can be dramatic: a previously cramped galley kitchen becomes a full-width open-plan room. Often includes a rooflight over the new section to bring in natural light.
Planning position: Often within Permitted Development on a terrace (the extension is not at the rear but to the side, with different PD limits). Conservation area designation or Article 4 may require full planning permission. The height and proximity to the boundary are the key tests.
Party wall: The side return is typically built up to or on the boundary with the neighbouring property, making party wall notices to the adjacent owner almost certain. The Act applies when new foundations are within 3 metres of the adjoining owner’s structure.
Cost range (London): £50,000–£95,000. The cost depends on how far back the extension runs, the rooflight specification, and whether structural changes are needed to the existing rear wall.
Wraparound Extension
What it is: A combination of a rear extension and a side return extension, creating an L-shaped addition at the back and side of the ground floor. The two parts are usually designed as a single open-plan space.
Typical size: 3–5 metres deep at the rear, 1.5–3 metres wide in the side return, creating an L- or U-shaped footprint.
Best for: Victorian and Edwardian terraces where both rear garden space and a side return are available. Produces the largest ground-floor open-plan spaces achievable in London terrace housing without structural changes above.
What you get: The most generous ground-floor extension type available on a terrace. Typically creates a kitchen-diner-living room of 35–55 square metres, with garden-facing glazing at the rear and a rooflight over the side return to bring light into the centre of the plan.
Planning position: The rear element may fall within PD; the side element has different PD rules. In practice, the combined scheme usually triggers a planning application both because of the combined scale and because most inner London streets with Victorian terraces are in or adjacent to conservation areas. A pre-application discussion with the local planning authority is worthwhile before commissioning detailed drawings.
Party wall: Applies at both the rear (if within 3 metres of the adjoining structure) and at the side return boundary. Notices must be served on all adjoining owners. A mid-terrace wraparound can involve notices to two neighbouring owners.
Cost range (London): £90,000–£160,000. The wraparound costs more than either element alone because of the complexity of the L-shaped roof and the longer run of foundations.
Two-Storey Side Extension
What it is: An extension built to the side of the property on two full floors, typically adding a new bedroom above and a larger room (utility, study, or garage replacement) below. Common on semi-detached houses with a driveway or gap to the side.
Typical size: 3–5 metres wide, matching the full height of the host building.
Best for: Semi-detached or detached houses with adequate space to the side. Less suitable for mid-terraces where the side space is too narrow.
What you get: Substantial additional floor area on both levels. Can convert a three-bedroom semi into a five-bedroom house when combined with a loft conversion, making it attractive in family-oriented outer London boroughs.
Planning position: Almost always requires full planning permission. Under PD, a two-storey side extension is limited to half the width of the original house and must set back from the front elevation. In practice, many applicants seek a full planning application to maximise the scheme. Extensions that would create a joined-up terrace (converting a semi into an effective terrace with the neighbour) are typically refused.
Party wall: Applies if the extension sits within 3 metres of the boundary with an adjoining owner, or if excavation affects their foundations.
Cost range (London): £95,000–£190,000, reflecting the structural complexity of a full two-storey addition and the higher specification typical of semi-detached properties in outer London.
Over-Structure Extension
What it is: An extension built above an existing single-storey element, typically a garage, utility room, or flat-roof rear addition adding first-floor space without extending the building’s footprint.
Typical size: Matches the existing structure below; typically 15–30 square metres of new floor area.
Best for: Properties where the ground-floor footprint is already at its maximum, but an existing single-storey structure offers a platform for a new bedroom, bathroom, or study above.
What you get: Additional bedroom or bathroom space at first-floor level, usually accessed off the existing landing. Does not increase the ground-floor footprint.
Planning position: Depends on the height relative to the existing building. If the over-structure element does not exceed the height of the main roof, it may fall within PD. If it raises the roof profile, planning permission is almost always required. Conservation area rules and any existing flat-roof extensions are key factors.
Party wall: Applies where the work involves any new load on structures within 3 metres of an adjoining owner, or where the existing single-storey element is a shared or party structure.
Cost range (London): £45,000-£90,000 lower than a full extension because no new foundations are required, but a structural assessment of the existing roof or ceiling to support the new floor above is always needed.
Which Extension Type Suits Which London Property?
| Extension Type | Best For | Typical Size | London Cost Range | Planning |
|---|---|---|---|---|
| Single-storey rear | Terraces, semis, post-war houses | 3–6m deep, full or part width | £50,000–£120,000 | PD or Planning |
| Two-storey rear | Houses needing bedroom + ground-floor space | 3–6m deep, one or two floors | £85,000–£180,000 | Planning required |
| Side return | Victorian & Edwardian mid-terraces | 1.5–3m wide, 5–8m long | £50,000–£95,000 | PD or Planning |
| Wraparound | Victorian & Edwardian terraces with side return | L-shaped: rear 3–5m + side 1.5–3m wide | £90,000–£160,000 | Planning usually required |
| Two-storey side | Semi-detached and detached houses | 3–5m wide, full height | £95,000–£190,000 | Planning required |
| Over-structure | Houses with existing single-storey garage or flat-roof addition | Matches structure below; 15–30m² | £45,000–£90,000 | PD or Planning |
| Basement | Central London where above-ground extensions are restricted | Full or partial footprint; 1 or 2 storeys down | £150,000–£350,000+ | Planning required |
All costs are London all-in ranges including structure, finishes, building regulations and VAT. Excludes architect and structural engineer fees, party wall surveyor costs, and furniture. Add 10–15% contingency.
Permitted Development (PD) allows certain extensions without a planning application, subject to size limits, height restrictions, and conditions. PD rights are removed or restricted in:
- Conservation areas (most of inner London is affected)
- Article 4 Direction zones (check with your local planning authority)
- Listed buildings and their curtilages
- Flats and maisonettes (PD does not apply to flats)
Prior Approval (Neighbour Consultation Scheme) extends the PD limits for single-storey rear extensions from 3 metres (terraces/semis) and 4 metres (detached) up to 6 metres and 8 metres respectively, subject to neighbour notification and the council’s agreement that there is no adverse impact on amenity.
Full planning permission is required for two-storey extensions, for anything exceeding PD limits, and for most projects in conservation areas. The householder application fee is £258 (as of 2026). Determination typically takes 8–13 weeks.
Lawful Development Certificate (LDC) is not required but strongly recommended if you intend to sell within five years. It provides formal confirmation that the works were lawful under PD. Cost: £129 for PD works.
For a full explanation of planning requirements for London renovations, see our guide to planning permission for a London renovation.
Check which: Types of House Extensions LondonÂ
How Do I Find Vetted House Extension Builders in London?
Finding a reliable house extension builder in London is not the same as finding one elsewhere in the country. The pool is large, the price variation is wide, and the difference between a builder who understands London’s planning constraints, party wall obligations, and period property quirks and one who does not can determine whether your project runs smoothly or stalls.
Before appointing any contractor, confirm four things. First, that they carry public liability insurance of at least £2 million; ask for the certificate, not just a verbal confirmation. Second, that they have completed a verifiable project of the same extension type in London within the last two years. A contractor who has built side return extensions in Lewisham will understand the party wall process and the lime mortar repairs a Victorian brick structure requires; one who has not may not. Third, that their quote is itemised by trade carpentry, plumbing, electrics, plastering, and groundworks separated out, not bundled into a single figure. Fourth, that the payment schedule is linked to completed stages, not demanded upfront.
Avoid any builder who cannot provide two or three references from recent London extension projects, and always call the references rather than reading written testimonials. Ask how they handled unexpected discoveries like buried drainage, unlevel floors, damp, because in London’s Victorian and Edwardian housing stock, surprises are the rule, not the exception.
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COMMON QUESTIONS
Frequently Asked Questions About Types of House Extensions in London
Questions homeowners ask us most often before submitting their brief.
What are the most common types of house extension in London?
Do I need planning permission for a house extension in London?
Which type of extension adds the most value to a London home?
What is a side return extension?
How much does a wraparound extension cost in London?
How long does a house extension take in London?
Do I need a party wall agreement for a house extension in London?
How do I find vetted extension builders in London?
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