ArchLocal Authority Profile
Spelthorne Borough Council
Adopted Documents We Assess Against
| Document | Type | Version | Monitor Status |
|---|---|---|---|
| Design of Residential Extensions and New Residential Development SPD | Residential Extensions SPD | Adopted April 2011 (Appendix 1C, Design Code Nov 2025) | Current checked 4 August 2026 |
Documents are re-checked against the council's own website weekly. A detected change flags "Policy Update Available" for human review — live assessment standards are never replaced automatically.
Spelthorne Borough Council standards at a glance
7 numeric standards taken from Spelthorne Borough Council's own adopted documents, each shown with the paragraph it comes from. Figures differ between councils — these are this one's.
Rear extension depth
Two storey rear
Roof form
Amenity neighbouring
Standards are what the council normally expects, not a guarantee. A scheme outside them can still be approved on its merits, and one inside them can still be refused for another reason.
Authored Policy Library
11 local policy checks, each citation-locked to the adopted document. National policy (NPPF, national space and daylight standards) applies alongside these.
Design of Residential Extensions and New Residential Development SPD
- Design of Residential Extensions SPD paragraph 3.47 — Rear extension depth A single-storey rear extension in Spelthorne should generally be no more than 3 metres high at the point nearest your boundary.
- Design of Residential Extensions SPD paragraphs 3.44, 3.46 — Two storey rear In Spelthorne a two-storey extension that adds more than half again to your house's footprint needs a stronger design case - and on a mid-terrace house, if both neighbours have already extended, a further extension that boxes the middle house in may not be acceptable at all.
- Design of Residential Extensions SPD paragraph 3.44 — Two storey rear The council flags a two-storey extension with a footprint greater than 50% of the original house as needing particular care and justification.
- Design of Residential Extensions SPD paragraph 3.56 — Roof alterations A dormer in Spelthorne should sit well inside the roof shape - about a metre in from the edges, half a metre down from the ridge, and a metre up from the eaves - centred on the roof rather than crammed to one side.
- Design of Residential Extensions SPD paragraph 3.56 — Roof form (3 checks) Keep the dormer at least 1m in from the side of the roof. Keep the top of the dormer at least 0.5m below the ridge. Keep the bottom of the dormer at least 1m above the eaves.
- Design of Residential Extensions SPD paragraphs 3.19-3.21 — Amenity neighbouring (2 checks) Spelthorne checks extensions against the standard BRE daylight tests - a 25-degree sightline from the neighbour's window, and a 45-degree arc for anything two-storey - to make sure their room and garden keep reasonable light. For a two-storey extension Spelthorne want a clear 45-degree arc from the middle of your neighbour's window. The 25-degree line and the patio overshadowing test are separate.
- Design of Residential Extensions SPD paragraph 3.14(a) — Amenity neighbouring Spelthorne want 21 metres back to back, made up of at least 10.5 metres of garden on each side. Three storeys pushes it to 30 metres.
- Design of Residential Extensions SPD paragraph 3.14(b) — Amenity neighbouring Where a blank side wall faces your back windows Spelthorne accept 13.5 metres. Put a habitable-room window in that side wall and the full 21 metres applies instead.