London Borough of Hillingdon

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 Hillingdon standards at a glance

13 numeric standards taken from London Borough of Hillingdon'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 3.3m

On a narrow plot in Hillingdon (under 5m wide), keep a single-storey rear extension to about 3.3 metres deep. HDAS paragraph 3.2

up to 3.6m

On a wider plot in Hillingdon a semi or terrace can normally take a 3.6-metre-deep rear extension. HDAS paragraph 3.3

up to 4m

A detached house in Hillingdon can normally take a 4-metre-deep single-storey rear extension. HDAS paragraph 3.4

up to 3m

A flat-roofed rear extension in Hillingdon should be no taller than 3 metres. HDAS paragraph 3.6

up to 3.4m

A pitched-roof rear extension in Hillingdon should top out at about 3.4 metres. HDAS paragraph 3.7

Side extension form

at least 0.25m

Keep the extension wall at least 25cm inside your boundary in Hillingdon so gutters and maintenance stay on your side. HDAS section 3 (side wall set-in)

Amenity space

at least 40m²

A 2-bed house in Hillingdon should keep at least 40 square metres of usable back garden after extending. HDAS paragraph 3.13

at least 60m²

A 3-bed house in Hillingdon should keep at least 60 square metres of usable back garden. HDAS paragraph 3.13

at least 100m²

A 4-bed (or bigger) house in Hillingdon should keep at least 100 square metres of usable back garden. HDAS paragraph 3.13

at least 60m²

A new 2-3 bed house in Hillingdon should have at least 60 square metres of usable private garden - less needs justifying, though a modest shortfall can pass on balance. Policy DMHB 18 / Table 5.3

Amenity neighbouring

at least 21m

Hillingdon expects at least 21 metres between facing habitable-room windows so neighbours are not overlooked. Policy DMHB 11 (residential amenity guidance)

Amenity internal

at least 11.5m²

In Hillingdon a new home's double bedroom must reach the 11.5 square metre standard as adopted local policy, not just national guidance. Policy DMHB 16 Housing Standards, applying the nationally described space standard

at least 7.5m²

A single bedroom in a new Hillingdon home must be at least 7.5 square metres as adopted local policy. Policy DMHB 16 Housing Standards, applying the nationally described space standard

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

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

HDAS: Residential Extensions SPD

• HDAS paragraph 3.2 — Rear extension depth On a narrow plot in Hillingdon (under 5m wide), keep a single-storey rear extension to about 3.3 metres deep.
• HDAS paragraph 3.3 — Rear extension depth On a wider plot in Hillingdon a semi or terrace can normally take a 3.6-metre-deep rear extension.
• HDAS paragraph 3.4 — Rear extension depth A detached house in Hillingdon can normally take a 4-metre-deep single-storey rear extension.
• HDAS paragraph 3.5 — Rear extension depth Hillingdon's depth allowances count from the house's original back wall - a second bite on an already-extended house usually busts the limit.
• HDAS paragraph 3.6 — Rear extension depth A flat-roofed rear extension in Hillingdon should be no taller than 3 metres.
• HDAS paragraph 3.7 — Rear extension depth A pitched-roof rear extension in Hillingdon should top out at about 3.4 metres.
• HDAS paragraph 3.8 — Amenity neighbouring Hillingdon does not want doors onto extension flat roofs - a makeshift balcony overlooks the neighbours.
• HDAS section 3 (side wall set-in) — Side extension form Keep the extension wall at least 25cm inside your boundary in Hillingdon so gutters and maintenance stay on your side.
• HDAS paragraph 3.13 — Amenity space (3 checks) A 2-bed house in Hillingdon should keep at least 40 square metres of usable back garden after extending. A 3-bed house in Hillingdon should keep at least 60 square metres of usable back garden. A 4-bed (or bigger) house in Hillingdon should keep at least 100 square metres of usable back garden.

Hillingdon Local Plan: Part 2 - Development Management Policies (2020)

• Policy DMHB 11 (residential amenity guidance) — Amenity neighbouring Hillingdon expects at least 21 metres between facing habitable-room windows so neighbours are not overlooked.
• Policy DMHB 16 Housing Standards, applying the nationally described space standard — Amenity internal (2 checks) In Hillingdon a new home's double bedroom must reach the 11.5 square metre standard as adopted local policy, not just national guidance. A single bedroom in a new Hillingdon home must be at least 7.5 square metres as adopted local policy.
• Policy DMHB 18 / Table 5.3 — Amenity space A new 2-3 bed house in Hillingdon should have at least 60 square metres of usable private garden - less needs justifying, though a modest shortfall can pass on balance.
• Policy DMH 6 — Design character Building a new home on garden land in Hillingdon starts from a presumption against - the scheme has to earn its place on neighbour amenity, access and modest scale, which is a judgement call for a planning professional.