Single-Storey Rear Extension: Permitted Development and Build Checklist
Quick Answer: In England a single-storey rear extension can often be built under permitted development without a full planning application: up to 3m deep for terraced/semi-detached and 4m for detached houses, or up to 6m/8m via the Neighbour Consultation Scheme (prior approval). Maximum height is 4m, with eaves no higher than 3m within 2m of a boundary, and you must not cover more than 50% of the curtilage. Permitted development is not exemption from Building Regulations — Parts A, B, C, F, K, L, M, P and H all still apply.
Summary
A single-storey rear extension is the most common domestic build in the UK, and the rules that govern it split into two separate systems people constantly confuse: planning (can I build it?) and Building Regulations (is it built safely and to standard?). Many rear extensions need no planning application at all because they fall within "permitted development" rights granted by the Town and Country Planning (General Permitted Development) (England) Order 2015 (GPDO). But every habitable extension must still comply with the Building Regulations and be signed off by building control — the two are entirely independent approvals.
Under permitted development, a single-storey rear extension can extend up to 3m beyond the original rear wall for an attached house (terraced or semi-detached) and 4m for a detached house. Larger extensions — up to 6m (attached) or 8m (detached) — can be allowed through the Neighbour Consultation Scheme, a "prior approval" process where the council notifies neighbours and only refuses if there are valid objections about impact. The height ceiling is 4m overall, eaves are capped at 3m where the extension is within 2m of a boundary, and the extension (with all other outbuildings) must not cover more than half the original garden/curtilage. These limits assume a standard house with intact permitted development rights — flats, maisonettes, listed buildings, conservation areas and homes under an Article 4 direction lose some or all of these rights.
The trap for clients and inexperienced builders is treating "I don't need planning" as "I don't need anything". A rear extension touches almost every part of the Building Regulations: structure (Part A) for the new beams and foundations, fire safety (Part B) for escape and protected routes, moisture (Part C) for the floor and walls, ventilation (Part F), protection from falling/glazing (Part K), conservation of fuel and power (Part L) for insulation and U-values, access (Part M), electrical safety (Part P) and drainage (Part H) if you build near or over a drain. Add party wall obligations where you build on or near a boundary, and the job is far more than four walls and a roof.
Key Facts
- GPDO 2015 — permitted development rights for single-storey rear extensions sit in the General Permitted Development Order.
- Depth — standard — up to 3m beyond the original rear wall (terraced/semi), 4m (detached).
- Depth — larger (prior approval) — up to 6m (terraced/semi) or 8m (detached) via the Neighbour Consultation Scheme.
- Maximum height — 4m overall for a single-storey rear extension.
- Eaves limit — eaves no higher than 3m if within 2m of a boundary.
- 50% curtilage rule — extensions plus outbuildings must not cover more than half the land around the original house.
- "Original house" — measured from the house as built or as it stood on 1 July 1948, not its current footprint.
- Materials — exterior should be similar in appearance to the existing house under PD.
- No PD on flats/maisonettes — householder permitted development does not apply.
- Article 4 / conservation areas / listed — permitted development can be reduced or removed; check the LPA first.
- Building Regulations always apply — Parts A, B, C, F, K, L, M, P and H as relevant.
- Party Wall etc. Act 1996 — notice required for excavation near, or building on, a boundary line.
- Building control — full plans or building notice; inspections at foundation, DPC, drainage and completion.
- CDM 2015 — applies to domestic projects; the client's duties usually pass to the contractor/principal contractor.
Quick Reference Table
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Try squote free →| Limit | Attached (terraced/semi) | Detached |
|---|---|---|
| Standard PD depth | 3m | 4m |
| Larger (prior approval) depth | 6m | 8m |
| Max overall height | 4m | 4m |
| Eaves within 2m of boundary | 3m max | 3m max |
| Curtilage coverage | ≤50% of original | ≤50% of original |
| Front of principal elevation | Not permitted | Not permitted |
| Flats/maisonettes | No PD | No PD |
Detailed Guidance
Step 1 — Establish the planning route
Single-storey rear extension — which route?
|
Is it a house (not a flat)? -- No --> Full planning application
| Yes
Conservation area / listed / Article 4? -- Yes --> Check LPA; likely full application
| No
Within standard PD limits (3m/4m, 4m high, 50% rule)? -- Yes --> Permitted development*
| No
Within larger limits (6m/8m)? -- Yes --> Prior approval (Neighbour Consultation Scheme)
| No
Exceeds all PD limits --> Full planning application
*A Lawful Development Certificate is strongly recommended even for permitted development — it's proof for future sale that the work was lawful. See permitted development rights and permitted development householder.
Step 2 — The Neighbour Consultation Scheme (larger extensions)
For depths between the standard limit and 6m/8m you don't make a full planning application — you submit a prior approval notification. The council writes to adjoining neighbours; if any object within the consultation period, the council assesses the impact on amenity (light, overshadowing, overbearing) and decides. No objection means you can proceed. You must notify before starting and cannot begin until the process concludes.
Step 3 — Building Regulations that apply
| Part | What it covers on a rear extension |
|---|---|
| A — Structure | Foundations, new openings, steel beams, lintels |
| B — Fire safety | Escape windows, protected routes, alarms |
| C — Site/moisture | DPC, DPM, ground contamination, weather resistance |
| F — Ventilation | Background and purge ventilation, kitchen/utility extract |
| H — Drainage | Building over/near drains, surface water, foul connection |
| K — Protection from falling/collision | Glazing, steps, level thresholds |
| L — Conservation of fuel/power | Wall/floor/roof U-values, glazing, airtightness |
| M — Access | Level/accessible thresholds where applicable |
| P — Electrical safety | New circuits, kitchen/bathroom electrics |
Building control sign-off comes via either a full plans application (drawings checked before work) or a building notice (suited to straightforward jobs); see building control process and building control.
Step 4 — Foundations and structure
Foundation type follows the ground and any nearby trees — strip, trench-fill or, on poor ground, raft or piled. Proximity to trees can demand deeper foundations to resist clay heave/shrinkage. The new opening into the existing house needs a steel beam or lintel sized by a structural engineer with calculations for building control. See foundations, structural calculations and steel beam installation. If you excavate within 3m (or build on the line of a boundary) the Party Wall etc. Act 1996 bites — serve notice in good time; see party wall and party wall notice templates.
Step 5 — Build sequence checklist
[ ] Confirm planning route (PD / prior approval / full) + Lawful Development Cert
[ ] Building control application (full plans or building notice)
[ ] Structural calcs for beams/foundations
[ ] Party wall notices served (if applicable)
[ ] CDM 2015 — appoint roles, F10 if notifiable
[ ] Set out; locate and protect existing drains (Part H build-over)
[ ] Excavate foundations — building control inspection BEFORE concrete
[ ] Pour foundations; build up to DPC — inspection at DPC
[ ] Oversite, DPM, insulation, concrete/beam-and-block floor
[ ] Cavity walls with insulation; install lintels/steel + padstones
[ ] Roof structure (flat warm-deck or pitched); weathertight
[ ] First fix: electrics (Part P), plumbing, ventilation ducting
[ ] Form/structural opening into existing house with temporary support
[ ] Insulate to Part L U-values; airtightness
[ ] Second fix; plaster; glazing (Part K safety glass)
[ ] Drainage connection inspection
[ ] Final building control inspection + completion certificate
Step 6 — Drainage and building over drains
If the extension sits over or within 3m of a public sewer you need a build-over agreement with the water company, and Part H governs how you protect the drain. Surface water from the new roof should follow the discharge hierarchy — see suds design and building regs part h drainage.
Frequently Asked Questions
If it's permitted development, do I still need building control?
Yes — always. Planning and Building Regulations are separate. Permitted development means you don't need planning permission; the extension must still be designed and built to the Building Regulations and signed off by building control. Skipping this leaves the work unlawful and unsellable.
How is the 3m/4m depth measured?
From the original rear wall of the house — "original" meaning as built, or as it stood on 1 July 1948 for older houses — not from any previous extension. A house that has already been extended at the rear has effectively used up its rear-extension allowance. Verify the exact measuring rules against the current GPDO before quoting.
What's the difference between the 3m/4m and 6m/8m limits?
The smaller depths are full permitted development needing no application (a Lawful Development Certificate is still wise). The larger depths require prior approval under the Neighbour Consultation Scheme — you must notify the council and neighbours and wait for the process before starting. These figures should be checked against the current Order.
Do these rules apply in Scotland and Wales?
No. The GPDO depths and the Neighbour Consultation Scheme are England-specific. Scotland and Wales have separate permitted development regimes and Building Standards/Regulations. Always use the correct national guidance.
Do I need a party wall agreement?
If you build on the boundary line, or excavate within 3m of a neighbour's structure to a depth below their foundations (or within 6m in certain cases), the Party Wall etc. Act 1996 requires you to serve notice. It's a legal process separate from planning and building control — start it early to avoid delaying the build.
Regulations & Standards
Town and Country Planning (GPDO) (England) Order 2015 — permitted development rights for rear extensions.
Building Regulations 2010 (Approved Documents A, B, C, F, H, K, L, M, P) — construction standards for the extension.
Party Wall etc. Act 1996 — boundary excavation and party structure works.
Construction (Design and Management) Regulations 2015 (CDM) — health and safety duties on domestic projects.
Neighbour Consultation Scheme — prior approval route for larger single-storey rear extensions.
Planning Portal: Single-storey rear extensions — permitted development limits.
The Town and Country Planning (GPDO) (England) Order 2015 — permitted development legislation.
GOV.UK: Building regulations approval — building control process.
GOV.UK: Party Wall etc. Act 1996 guidance — boundary works.
permitted development rights — full permitted development rules for houses.
building control process — getting building control sign-off.
party wall — party wall notices and awards.
foundations — choosing and building extension foundations.