Extensions in Enfield: The 2026 Planning Checklist
Extending your home is still the most reliable way to add space and value in Enfield — and the borough decides extension applications on some of the most precise geometric rules in London. This checklist covers the question the old guides skip (do you even need planning permission?), and then the exact tests Enfield applies when you do.
First: permission, or permitted development?
A large share of Enfield extensions don't need a planning application at all. Householder permitted development rights allow single-storey rear extensions to 3 m (terraced/semi) or 4 m (detached) — and up to 6 m / 8 m under the prior-approval "larger home extension" route — plus loft conversions, outbuildings and more, subject to strict technical limits. We've set those out in our householder permitted development guide.
Two cautions. First, PD is property-specific — conservation areas, flats, removed PD rights and previous extensions all change the answer, so confirm it with a Lawful Development Certificate (Proposed) before you build. Second, if your scheme exceeds the PD envelope — deeper, wider, higher, or on designated land — you're into a householder planning application, and the rest of this checklist is what Enfield will judge it against.
The policy framework
Enfield assesses householder applications against its adopted Development Management Document (DMD, 2014) — principally DMD 11–14 for the extension types, supported by DMD 8 (general standards), DMD 9 (amenity space) and DMD 10 (distancing) — under the umbrella of Core Strategy Core Policy 4 (design quality) and the London Plan. One eye on the future: Enfield's new Local Plan is in its final examination stages and will eventually replace the DMD — the rules below are current today, but check the position before submitting (where the new plan stands).
1. Rear extensions (Policy DMD 11)
Single-storey depth: max 3 m beyond the original rear wall (terraced and semi-detached); 4 m for detached.
Single-storey height: flat roof — max 3 m to the eaves from ground level, with 3.3–3.5 m allowed to the top of a parapet; pitched roof — max 4 m at the ridge and 3 m at the eaves.
The 45° rule (ground floor): the extension must not cross a line taken at 45° from the midpoint of the neighbour's nearest original ground-floor window.
The 30° rule (first floor): first-floor extensions must not cross a 30° line from the midpoint of the neighbour's nearest original first-floor window.
Common alignment: where neighbouring extensions exist, a deeper extension may be acceptable if it secures a common rear building line — and conversely, alignment may be required.
Amenity retention: adequate garden space must remain (DMD 9 sets the minimums — e.g. 38 m²+ average for family dwellings without communal space), and access to existing garages/parking must be kept.
2. Outbuildings (Policy DMD 12)
Strictly ancillary to the main dwelling (a garden office or gym, not a separate unit).
Not normally projecting forward of the front building line.
Adequate separation from the house; height and bulk that don't harm neighbouring amenity or local character; design respecting the topography.
Remember many garden buildings are PD under Class E (max 2.5 m within 2 m of a boundary) — the DMD 12 tests apply when you're outside those limits or in a constrained location.
3. Roof extensions and dormers (Policy DMD 13)
Dormers must sit within the roof plane, inset from eaves, ridge and roof edges — typically 500–750 mm.
The addition must read as subordinate: not dominant from the street, in keeping with the property's character.
Side dormers must not unbalance a pair or group (the classic semi-detached symmetry problem).
Front dormers are generally resisted unless they genuinely don't affect the area's character.
The PD alternative: Class B allows up to 40 m³ (terraced) or 50 m³ of additional roof space without an application, subject to its own limits — often the smarter route where it fits.
4. Side extensions (Policy DMD 14)
Keep a minimum of 1 m to the side boundary to avoid the "terracing effect" — more where plot size or street character demands it.
No continuous façade out of character with the locality.
Corner plots: maintain separation from the back edge of the pavement on the return frontage, judged on building lines and vistas, visibility splays, subordination of the extension, and retained amenity space.
The neighbour tests that decide marginal cases (DMD 8 + 10)
Beyond the per-type rules, Enfield applies general standards that catch borderline schemes: preserve neighbours' daylight, outlook and privacy; meet the distancing standards (e.g. 22 m between facing rear habitable windows for 1–2 storey relationships, rising to 25–30 m with height, and 11 m from windows to side boundaries); keep hardstandings and boundary treatments from dominating the street scene (front boundaries normally max 1 m high). If your design fails these, no amount of compliance with the depth limits will save it.
Design quality and sustainability (Core Policy 4)
Core Policy 4 is the golden thread: high-quality design, materials that integrate with the host building, and sustainable construction. In 2026 terms that means designing to current Building Regulations Part L energy standards (the Code for Sustainable Homes referenced in older guidance was withdrawn years ago), considering accessibility under Part M where relevant, and showing the extension preserves the architectural integrity of the house. A short, well-judged design statement addressing these often separates approval from refusal on marginal schemes.
Cost and process
A householder planning application costs £548 from 1 April 2026 — £639 submitted via the Planning Portal with its service charge — with a target determination period of 8 weeks. An LDC (Proposed) to confirm a PD scheme runs at half the fee. Budget separately for drawings, any required reports (trees, flood risk in Zones 2–3, heritage statements in conservation areas) and Building Regulations approval, which applies whichever planning route you take. Party wall notices are a separate legal layer again — one we also handle.
Common pitfalls
Designing to the PD limits, then adding "just a bit more" without realising you've crossed into application territory.
Measuring depth from a previous extension rather than the original rear wall.
Ignoring the 45°/30° tests until the neighbour objection arrives.
Forgetting DMD 9's retained-garden minimums on smaller plots.
Treating Building Regulations and party wall matters as afterthoughts.
Get it right first time
Enfield's rules are precise, which cuts both ways: schemes designed to the policy pass smoothly, and schemes designed around it get caught. Bashkal designs and manages Enfield extensions end to end — feasibility against the DMD tests, drawings, the application or certificate, and Building Regulations. If you're planning an extension in Enfield, contact us before you commission drawings.
Verified 5 June 2026 against the adopted Enfield DMD (November 2014), Policies DMD 8–14; Core Strategy (2010) Core Policy 4; and the Planning Portal fee schedule (1 April 2026). Enfield's new Local Plan was under examination and not adopted at the date of writing — confirm the current policy position before submitting.
