Single Storey Extension Ideas for London Homes

Last updated: August 2026 · Verified against current government planning rules and London council records.

What are the best single storey extension ideas for a London home?

Quick answer: Three footprints do most of the work in London: the full-width rear extension, the side-return infill and the L-shaped wraparound that combines the two. Choose the footprint to match your house type, then choose the roof — flat with lanterns, pitched, or part-glazed at the junction — to control light and height. Permitted development allows 3m of rear depth on a terraced or semi-detached house and 4m on a detached one, extendable to 6m or 8m through prior approval, and those numbers shape more London extension designs than anything an architect draws freehand.

London's housing stock rewards specific moves. A Victorian terrace in Haringey or Islington almost always has a dark side return begging to be enclosed; a 1930s semi in Barnet or Enfield usually has the garden depth for a full-width rear addition. This guide covers the footprints, the roofs and the junction between old and new — for a broader tour of styles and layouts, see our roundup of extension ideas for London homes.

Rear, side return or wraparound — which footprint suits your house?

The footprint decision is mostly made for you by the house you own. Terraces gain the most from the side return, because the extension adds width where the kitchen is narrowest without eating garden. Semis and detached houses gain more from straight rear depth, and corner or end-of-terrace plots can often run an L-shaped wraparound that delivers both.

Footprint	Best suited to	What it delivers	Watch out for
Full-width rear	1930s semis and detached houses in Barnet, Enfield and Southgate	A wide kitchen-diner across the whole back of the house, with garden views from every corner	PD depth caps at 3m (terraced/semi) or 4m (detached) without prior approval; deep plans need rooflights
Side return	Victorian terraces in Haringey, Islington and Camden	Width where the galley kitchen is tightest, with little or no garden lost	Party wall notices to the neighbour; eaves capped at 3m within 2m of the boundary
Wraparound (L-shape)	End-of-terrace and semi-detached corner plots	The most flexible layout — kitchen, dining and a family zone in one connected space	Combining rear and side almost always means a full planning application

Side returns punch far above their size. A typical Victorian side return is barely more than a metre and a half wide, yet enclosing it turns a galley kitchen into a proper family room. We cover the structural detail — steels, boundary walls, drainage in the old alley — on our side return extensions page.

Which roof makes the space — flat with lanterns, pitched, or part-glazed?

The flat roof with one or two rooflanterns is the default London choice for good reason. Permitted development caps a single storey extension at 4m high, and a flat roof uses that allowance efficiently while a lantern drops daylight into the centre of a deep plan where windows cannot reach. Crisp parapet detailing also suits period and modern houses alike.

A pitched roof earns its place on conservation-area streets and wherever the extension is visible from the side. It reads as part of the original house rather than an addition, and inside it allows a vaulted ceiling that makes a modest footprint feel far larger. The constraint within 2m of a boundary is the eaves rule — permitted development holds eaves to 3m there, which is why so many London side returns end up as a lean-to pitch falling towards the neighbour's wall.

Part-glazed roofs — a glass strip where new roof meets old wall — solve the most common London problem of all: the middle of the original house going dark once you extend past it. A metre of glazing along the junction lights the old rear reception without the heat management headaches of a fully glazed roof.

How do you connect the old house to the new room?

The junction is where extensions succeed or fail. Removing the whole rear wall gives one big open space, but many families now prefer broken-plan: a wide structural opening with a retained nib or a run of slim-framed glazing, so kitchen noise stays out of the snug. Keeping the original rear reception as a utility, pantry or playroom often makes better use of a terrace plan than knocking everything through.

Get the levels and finishes agreed on the drawings, not on site. A level threshold from old floor to new, one continuous floor finish, and door heads aligned with the original openings make new work feel inevitable rather than bolted on. A good extension builder will set the steelwork to carry those clean lines — the box gutter, the flush ceiling, the hidden downstand — because retrofitting them afterwards is miserable work.

When do permitted development limits shape the design?

Under permitted development a single storey rear extension can run 3m from the original rear wall of a terraced or semi-detached house and 4m from a detached one, up to 4m high. The larger-home prior approval route extends that to 6m and 8m respectively — a neighbour-consultation process with a £249 fee rather than a full application. Side extensions have their own rules: single storey only, no more than half the width of the original house, and nothing forward of the principal elevation.

Those limits explain the shape of most London extensions. The 3m line is why so many semi rear additions stop where they do, the 3m eaves rule near boundaries is why side returns lean, and the half-width rule is why side extensions on 1930s semis stay modest. Conservation areas and Article 4 directions — common across Camden, Islington and pockets of Haringey and Barnet — remove specific rights entirely, and flats and maisonettes have no householder permitted development rights at all.

Where a design steps outside the limits, a householder application costs £548 from 1 April 2026 plus the Planning Portal's £91.02 payment charge, with a decision due eight weeks from validation. Even a fully compliant scheme is worth certifying with a Lawful Development Certificate at £274 — solicitors ask for it when you sell. The full breakdown is in our guide to extension planning fees.

What does a single storey extension cost?

Every project is priced individually — footprint, roof choice, glazing and groundworks move the number too much for a per-square-metre figure to mean anything. We survey the house, then issue a fixed, itemised quote after a free site visit, so the only costs you carry beyond it are the statutory ones above. Our extension cost guide explains what drives the price up or down before you commit to drawings.

Frequently asked questions

How deep can a single storey extension go without planning permission?
3m from the original rear wall on a terraced or semi-detached house, 4m on a detached one. Prior approval can extend that to 6m and 8m respectively for a £249 fee, subject to neighbour consultation.

Does a roof lantern need planning permission?
Not usually. A lantern on a permitted development extension is fine provided the extension stays within the 4m maximum height overall. In conservation areas, check before ordering — Article 4 directions can change the position.

Can I build a wraparound extension under permitted development?
Rarely. Combining a rear and side extension in one L-shape usually takes the scheme outside permitted development, so most London wraparounds go through a full householder application — £548, decided within eight weeks of validation.

I own a flat with a garden — do these rules apply to me?
No. Flats and maisonettes have no householder permitted development rights, so any extension needs a full planning application regardless of size.

Do I need party wall notices for a single storey extension?
On most terraces and semis, yes — building at the boundary and excavating within 3m of a neighbour's structure and deeper than its foundations both trigger the Party Wall Act. We serve the notices for clients as standard and run the party wall clock in parallel with the eight-week planning period.