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Two-storey rear extension: do I need planning permission? (England, 2026)

For homeowners in England. Updated 2026-06-17.

Overview

A two-storey rear extension can be permitted development, but the rules on depth and distance from the rear boundary are strict — and London terraces with short gardens usually fail them.

The permitted-development rules

Permitted development requires the extension to be within 3m of the original rear wall, at least 7m from the rear boundary, and no higher than the existing eaves. It is never permitted development on designated land. Most London terraces fail the 7m rule and need full planning permission.

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)

A two-storey rear extension needs building-regulations approval, separately from planning — the extra floor adds structural and party-wall considerations:

  • Part A — Structure: Foundations, beams and lintels, strengthening of the existing structure, and any new floor.
  • 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.
  • Party Wall etc. Act 1996 (separate law): Work on or beside a shared boundary or party wall may require party-wall notices served on neighbours — independent of planning and building control.

Check your planning route

Answer a few questions about your home and your plans. No email or sign-up — your verdict shows straight away.

  1. 1 Postcode
  2. 2 Property
  3. 3 Plans
  4. 4 Details
  5. 5 History
What's your postcode?

We use it once to look up your borough and the planning record — it isn't stored with your details.

Frequently asked questions

Do you need planning permission for a two-storey (double-storey) extension?
Often, yes. A two-storey rear extension can be permitted development, but the limits are tight: it must be within 3m of the original rear wall, at least 7m from the rear boundary, and no higher than the existing eaves. It is never permitted development on designated land, and many London terraces fail the 7m rule and need full planning permission.
How big can a two-storey extension be without planning permission?
Under permitted development a two-storey rear extension can project no more than 3m beyond the original rear wall — and unlike a single-storey extension, there is no 6m or 8m "larger home" option for two storeys. It must also stay at least 7m from the rear boundary and no higher than the existing eaves.
How close to the boundary can a two-storey extension be? (the 7m rule)
For permitted development, a two-storey rear extension must be at least 7 metres from the rear boundary at its closest point. Gardens shorter than that — common on London terraces — put the extension outside permitted development, so it needs a full householder planning application instead.
Can you build a two-storey side extension under permitted development?
No. Permitted-development rights for side extensions are limited to single storey, no wider than half the original house and no more than 4m high. A two-storey side extension falls outside Class A and needs a full householder planning application — and it is excluded entirely on designated land.
Does a two-storey extension need building regulations?
Yes, always. Building control checks the structure including the new upper floor (Part A), thermal performance (Part L), damp-proofing (Part C), drainage and any build-over-sewer agreement (Part H), ventilation (Part F) and safety glazing (Part K). The Party Wall etc. Act 1996 often applies too — all separate from planning permission.
Can I put a two-storey extension on a semi-detached house?
Yes, in principle. A semi-detached house can take a two-storey rear extension under permitted development within the same limits — 3m beyond the original rear wall, 7m from the rear boundary, no higher than the existing eaves, and not on designated land. The shared boundary usually brings the Party Wall Act into play.
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.

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