Types of Home Extension in London: Which Is Right for You?

The single-storey rear extension is the most common home improvement project in London. It extends the rear of the house at ground floor level — typically to create a larger kitchen-diner or ground floor living space.

**Best for**: widening and deepening the ground floor of a Victorian or Edwardian terraced house; creating open-plan kitchen-diner; adding a utility room.

**Planning**: most are Permitted Development (PD) up to 3m deep for terraced/semi (6m under the Larger Home Extension Scheme) and 4m for detached (8m under LHES). Full planning permission required beyond these limits and in Conservation Areas.

**Structural considerations**: new foundation strip, structural opening in the rear wall (RSJ), flat or pitched roof. Straightforward for most London terraces.

**Typical cost (London 2026)**: £45,000–£130,000 depending on size and specification.

**Programme**: 12–18 weeks on site.

The side return extension fills in the narrow alleyway that runs alongside the rear addition of most Victorian and Edwardian terraced houses. The side return (typically 1.0–1.8m wide) is infilled to widen the ground floor.

**Best for**: widening the rear ground floor plan of a Victorian terrace without extending rearward; gaining additional kitchen or dining space without a deeper rear extension.

**Planning**: usually requires planning permission (side elevation extension; exceeds PD width rules for terraced houses). Routinely approved across London boroughs.

**Structural considerations**: party wall notices to left-side neighbour; foundation strip along party wall line; glazed roof (often recommended to replace lost light from the side return window); structural connection to existing rear addition wall.

**Typical cost (London 2026)**: £35,000–£90,000 depending on width, roof specification, and finish.

**Programme**: 10–16 weeks on site.

The wraparound extension is a combination of a rear extension and a side return infill, creating an L-shaped footprint. It is the most impactful single ground floor change available to a Victorian London terrace.

**Best for**: maximum ground floor area gain from a single project; creating a large, fully open-plan ground floor with defined zones; transforming a dark, fragmented Victorian ground floor into a light-filled modern space.

**Planning**: requires planning permission (double-width and depth change; side elevation work). Usually approved but requires well-considered design and drawings.

**Structural considerations**: combines all the structural considerations of a rear extension plus a side return — RSJ opening to rear, party wall foundation and notices, glazed roof to side return, complex corner connection.

**Typical cost (London 2026)**: £70,000–£145,000 depending on the extent, specification, and roof arrangement.

**Programme**: 14–22 weeks on site.

A double-storey extension extends the building at both ground and first floor levels — adding both additional downstairs space and an additional bedroom (or bathroom) upstairs.

**Best for**: adding a bedroom as well as ground floor space; families who need both a larger kitchen and an additional bedroom; maximising value from a single build event.

**Planning**: always requires full planning permission — cannot be done under Permitted Development. Also triggers more detailed party wall considerations if adjacent to the boundary.

**Structural considerations**: full structural frame required; two-storey height party wall interaction; more detailed Building Regulations for upper floor (fire safety, sound, Part K guarding). Floor between ground and first floor must meet acoustic and structural requirements.

**Typical cost (London 2026)**: £90,000–£200,000 depending on size and specification. The cost per square metre is less than two separate extensions due to the shared structural, roof, and external elements.

**Programme**: 16–24 weeks on site.

An outbuilding or garden room is a separate structure in the garden, not connected to the main house. Garden rooms, home offices, gyms, studios, and garden annexes are all forms of outbuilding.

**Best for**: home offices, gyms, and creative studios where connection to the main house is not required; providing accommodation for a dependent relative (subject to planning conditions); maximising garden footprint without extending the main house.

• **Planning rules for outbuildings** (Permitted Development, Class E of the GPDO):
• •Single storey only (maximum height: 2.5m within 2 metres of a boundary, or 4m with a dual-pitch roof, 3m with any other roof, if more than 2m from a boundary)
• •Must not be closer to a highway than the existing house
• •Total area of all outbuildings plus the original extension must not exceed 50% of the original curtilage
• •Must not be in front of the principal elevation
• •Listed buildings: no PD rights — full planning required
• •Conservation areas: no PD for outbuildings in front of the house or forward of the rear elevation

**Habitable outbuildings (annexes)**: where an outbuilding is to be used as sleeping accommodation for a dependent relative, planning permission may be required (question of whether it becomes a separate dwelling unit). HMRC also has implications for properties with habitable annexes — consult a planning consultant.

• **Typical cost (London 2026)**:
• •Basic insulated garden room (15–20m²): £18,000–£35,000
• •Premium home office/studio with M&E and quality finish: £35,000–£70,000
• •Habitable annex with kitchen, bathroom, bedroom: £55,000–£110,000

**Programme**: 6–12 weeks on site.

The right extension type depends on several factors:

• **What do you need?**
• •Ground floor living space only → single-storey rear or side return
• •Ground floor + bedroom → double-storey or loft conversion (which adds upstairs without rear extension)
• •Ground floor kitchen transformation → wraparound
• •Separate space (office, gym, studio) → outbuilding/garden room

• **What does your property allow?**
• •Victorian terrace → best candidates for wraparound, side return, and loft conversions
• •Semi-detached or detached → more options for side extensions and double-storey
• •Conservation area → more restricted — full planning applies; materials requirements may add cost
• •Article 4 Direction area → PD rights may be removed entirely — check with the council

• **What is your budget?**
• •Under £50,000 → single-storey rear (smaller scheme) or side return
• •£50,000–£100,000 → single-storey rear (larger, quality finish) or wraparound (smaller)
• •£100,000–£200,000 → large wraparound, double-storey, or loft + rear extension combination

• **What is your programme tolerance?**
• •10–15 weeks: side return or small rear extension
• •14–20 weeks: wraparound or larger rear extension
• •18–26 weeks: double-storey or large complex scheme

A site visit and early design consultation with rcbGroup can help you understand which extension type best suits your property and goals before committing to architectural drawings.