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

Basement at 84.2% based on 482 decisions.

What is hardest to get planning permission for in Hillingdon?

Annex at 41.4% based on 128 decisions.

How do approval rates vary by project type in Hillingdon?

From 84.2% (Basement) to 41.4% (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 42.8% — that's the difference between near-certainty and a coin flip. What you build matters as much as where you build it.

30,584 real decisions·17 project types·Updated June 2026

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All 17 project types ranked

#	Type	Decisions	Approved	Refused	Rate
1	Basement	482	406	76	84.2%
2	Hip-to-Gable Conversion	2,252	1,881	371	83.5%
3	Extension (General)	1,988	1,650	338	83.0%
4	Conservatory	852	698	154	81.9%
5	Garage / Parking	7,611	6,162	1,449	81.0%
6	New Build	1,672	1,345	327	80.4%
7	Outbuilding	2,618	2,099	519	80.2%
8	Dormer	4,882	3,831	1,051	78.5%
9	Rear Extension	10,118	7,872	2,246	77.8%
10	Wraparound Extension	983	748	235	76.1%
11	Change of Use (Residential)	1,480	1,101	379	74.4%
12	Loft Conversion	487	362	125	74.3%
13	Flat Conversion	917	670	247	73.1%
14	Side Extension	4,825	3,434	1,391	71.2%
15	Front Extension	1,069	701	368	65.6%
16	HMO	339	195	144	57.5%
17	Annex	128	53	75	41.4%

See how this applies to your postcode →

These are council averages. Your property is specific.

A basement application has a 84.2% approval rate. Annex? Just 41.4%.
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What the data tells us

The range is massive: 41.4% to 84.2%. 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

6,410 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 30,584 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 present. Full methodology →