Single-storey rear extension: do I need planning permission? (England, 2026)
For homeowners in England. Updated 2026-06-17.
Overview
A single-storey rear extension is the most common project that qualifies for permitted development — but the depth limit depends on your property type, and a deeper extension may need prior approval or full planning.
The permitted-development rules
Permitted development allows a single-storey rear extension up to 3m deep on a terrace or semi-detached house, or 4m on a detached house, with a maximum height of 4m (eaves no higher than 3m if within 2m of a boundary). Beyond that, the Larger Home Extension scheme can allow up to 6m (terrace/semi) or 8m (detached) through prior approval — but not on designated land, where a full application is required.
Whether these rules apply to your home depends on any conservation area, Article 4 direction or listed-building status at your address. Check yours below.
Building regulations (separate from planning)
Building regulations apply separately from planning, and almost always to a rear extension. Building control checks the work against several Approved Documents:
- Part A — Structure: Foundations, ground conditions, beams and lintels, and strengthening of the existing structure.
- Part L — Energy: New thermal elements to current U-values (external wall 0.18 W/m²K; windows/doors 1.4 W/m²K); glazing generally limited to about 25% of floor area.
- Part C — Moisture: Damp-proofing and weatherproofing, with the floor membrane lapped to the existing damp-proof course.
- Part H — Drainage: Drainage connections, plus a build-over agreement with the water company if you build within 3m of a public sewer (or 1m of a lateral drain).
- Parts F & K — Ventilation and safety: Adequate background/purge ventilation, and safety glazing to new openings.
Check your planning route
Answer a few questions about your home and your plans. No email or sign-up — your verdict shows straight away.
Frequently asked questions
- Do I need planning permission for a single-storey rear extension?
- Often not. Under Class A permitted development a single-storey rear extension can be built without planning permission if it projects no more than 3m beyond the original rear wall (4m for a detached house) and is no more than 4m high. Larger projections, designated land or an Article 4 direction change this — the checker above confirms your exact position.
- How big can a single-storey rear extension be without planning permission?
- The standard permitted-development depth is 3m beyond the original rear wall for a terrace or semi-detached house, and 4m for a detached house, with a maximum height of 4m and eaves no higher than 3m within 2m of a boundary. All extensions and outbuildings together must not cover more than half the garden.
- What is the Larger Home Extension scheme (prior approval)?
- It lets you build a deeper single-storey rear extension — up to 6m on a terrace or semi-detached house, or 8m on a detached house — without full planning, through a prior-approval application. Your council notifies neighbours, who have 21 days to comment, and must determine it within 42 days. It is unavailable on designated land.
- Do I need planning permission for a rear extension in a conservation area?
- Yes, with tighter limits. On designated land such as a conservation area the Larger Home Extension scheme does not apply, so the standard 3m/4m depth limits stand and cladding the extension is not permitted development. An Article 4 direction can remove the right entirely, requiring full planning. The checker names any designation at your address.
- Do building regulations apply to a single-storey extension?
- Almost always — separately from planning. Building control checks the structure (Part A), thermal performance (Part L), damp-proofing (Part C), drainage including any build-over-sewer agreement (Part H), ventilation (Part F) and safety glazing (Part K). Planning permission and building regulations are two different approvals; you can need building regs even when the work is permitted development.
- Does a single-storey rear extension add value?
- It can. Nationwide Building Society’s House Price Index (November 2025) found that adding floor space and an extra bedroom is what drives value — a loft conversion or extension adding a double bedroom and bathroom can add as much as 24% to a three-bedroom, one-bathroom house. The realised figure depends on your local market and specification.
Sources and legal currency
Legal currency (mid-2026): GPDO 2015 householder Class A (extensions) and Class B (roof/loft) limits are unchanged — SI 2025/560 and SI 2026/313 did not amend them. The operative energy standard is the 2021 Part L uplift (in force 15 June 2022); the Future Homes Standard is delayed (the Building Regulations etc. (Amendment) (England) Regulations 2026 come into force 24 March 2027). Confirm exact U-values against the current Approved Document L at the point of build.
Other extension types
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Two-storey rear extension
Tight rules on boundary distance; often full planning in London.
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Side extension
Half the original width, single storey — and never on designated land.
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Wraparound extension
A combined side + rear assessment — usually full planning.
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Rooflight (Velux) loft conversion
Usually permitted development off designated land.
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Dormer loft conversion
Volume limits apply; not permitted on designated land.
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Hip-to-gable loft conversion
Class B volume limits; needs a hipped roof to start with.
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Mansard loft conversion
Almost always full planning permission.
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Additional storey (upward extension)
Class AA prior approval — strict age and height limits.
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Porch
Small porches are permitted development (Class D).
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Outbuilding / garden room
Curtilage and height limits under Class E.
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Garage conversion
Usually permitted development — unless a condition removed PD.