London Borough of Harrow

Adopted Documents We Assess Against

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.

London Borough of Harrow standards at a glance

3 numeric standards taken from London Borough of Harrow's own adopted documents, each shown with the paragraph it comes from. Figures differ between councils — these are this one's.

Rear extension depth

up to 3m

Where your rear extension in Harrow runs along the boundary, keep it to about 3 metres high there (a touch more - 3.5m - is allowed for a pitched roof measured to the middle of the slope). Residential Design Guide SPD paragraph 6.63

Side extension form

up to 3m

A single-storey side extension against the boundary in Harrow should generally be no more than about 3 metres high at that boundary. Residential Design Guide SPD paragraph 6.41

at least 1m

A two-storey side extension in Harrow should usually start at least 1 metre back from the front of the house, with a lower roofline - it keeps the house reading as an addition, not a semi turned into a terrace. Residential Design Guide SPD paragraph 6.8

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

7 local policy checks, each citation-locked to the adopted document. National policy (NPPF, national space and daylight standards) applies alongside these.

Residential Design Guide SPD

• Residential Design Guide SPD paragraph 6.63 — Rear extension depth Where your rear extension in Harrow runs along the boundary, keep it to about 3 metres high there (a touch more - 3.5m - is allowed for a pitched roof measured to the middle of the slope).
• Residential Design Guide SPD paragraph 6.41 — Side extension form A single-storey side extension against the boundary in Harrow should generally be no more than about 3 metres high at that boundary.
• Residential Design Guide SPD paragraph 6.8 — Side extension form A two-storey side extension in Harrow should usually start at least 1 metre back from the front of the house, with a lower roofline - it keeps the house reading as an addition, not a semi turned into a terrace.
• Residential Design Guide SPD paragraphs 6.64-6.65, 6.28-6.32 — Two storey rear A two-storey or first-floor rear extension in Harrow should not go higher than the existing roof, and on a mid-terrace house this kind of extension is very unlikely to be acceptable at all. Corner/end-of-terrace and semi-detached houses are judged against the 45 Degree Code protecting the neighbour's light and outlook.
• Residential Design Guide SPD paragraph 6.19 — Amenity neighbouring Harrow generally will not support extensions and outbuildings that together cover more than about half your rear garden.
• Residential Design Guide SPD paragraphs 6.68-6.72 — Roof alterations A rear dormer in Harrow needs to sit well inside the roof - clear of the party wall, the gable end and the eaves by roughly half a metre to a metre - and must never poke above the ridge.
• Residential Design Guide SPD paragraph 4.68 — Amenity neighbouring Harrow draw their 45-degree line from the CORNER of your neighbour's building, not from a window like most boroughs - so measure to the corner. It applies to two and three storey work, and the roof eaves count.