What type of planning application is most likely to be approved in Hillingdon?

Basement at 85.7% based on 477 decisions.

What is hardest to get planning permission for in Hillingdon?

Annex at 42.3% based on 130 decisions.

How do approval rates vary by project type in Hillingdon?

From 85.7% (Basement) to 42.3% (Annex). What you build matters as much as where you build it.

Most Common Planning Applications in Hillingdon

Not all planning applications are created equal. The gap between the highest and lowest approval project type in Hillingdon is 43.4% — that's the difference between near-certainty and a coin flip. What you build matters as much as where you build it.

30,835 real decisions·17 project types·Updated August 2026

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All 17 project types ranked

#	Type	Decisions	Approved	Refused	Rate
1	Basement	477	409	68	85.7%
2	Hip-to-Gable Conversion	2,310	1,941	369	84.0%
3	Extension (General)	2,013	1,686	327	83.8%
4	Conservatory	878	724	154	82.5%
5	Garage / Parking	7,631	6,248	1,383	81.9%
6	New Build	1,672	1,360	312	81.3%
7	Outbuilding	2,670	2,162	508	81.0%
8	Dormer	4,969	3,939	1,030	79.3%
9	Rear Extension	10,275	8,059	2,216	78.4%
10	Wraparound Extension	1,020	783	237	76.8%
11	Change of Use (Residential)	1,484	1,111	373	74.9%
12	Loft Conversion	498	370	128	74.3%
13	Flat Conversion	917	675	242	73.6%
14	Side Extension	4,872	3,497	1,375	71.8%
15	Front Extension	1,075	712	363	66.2%
16	HMO	347	203	144	58.5%
17	Annex	130	55	75	42.3%

See how this applies to your postcode →

These are council averages. Your property is specific.

A basement application has a 85.7% approval rate. Annex? Just 42.3%.
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What the data tells us

The range is massive: 42.3% to 85.7%. Choosing the right project type — or framing your application correctly — can dramatically affect outcomes.

Visibility drives scrutiny. Project types that change the external appearance — dormers, loft conversions, hip-to-gable — face more resistance than those that don't. The more visible your proposal, the more carefully it needs designing.

These are council-wide averages. Your ward, your street and your immediate neighbours all shift the odds. The comparable decisions near your property are the best indicator of outcome.

Before you spend £5,000+ on architects and drawings

6,178 planning applications in Hillingdon have been refused since 2020. Many of those homeowners had already paid for drawings and application fees. A free, property-specific report shows you what gets approved — and what gets refused — near your property.

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More Hillingdon planning data

Nearby councils project type rankings

Methodology: Classifies 30,835 decisions in Hillingdon into residential project types using keyword matching against proposal descriptions (matching generate_site_data.py subtype rules). A single application may appear in multiple categories. Data from Hillingdon Council's public planning portal, January 2020 to August 2026. Full methodology →