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

Flat Conversion at 92.2% based on 829 decisions.

What is hardest to get planning permission for in Harrow?

Annex at 42.6% based on 54 decisions.

How do approval rates vary by project type in Harrow?

From 92.2% (Flat Conversion) to 42.6% (Annex). What you build matters as much as where you build it.

Most Common Planning Applications in Harrow

Not all planning applications are created equal. The gap between the highest and lowest approval project type in Harrow is 49.6% — that's the difference between near-certainty and a coin flip. What you build matters as much as where you build it.

12,600 real decisions·17 project types·Updated March 2026

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All 17 project types ranked

#	Type	Decisions	Approved	Refused	Rate
1	Flat Conversion	829	764	65	92.2%
2	Basement	307	261	46	85.0%
3	Change of Use (Residential)	642	538	104	83.8%
4	Wraparound Extension	223	184	39	82.5%
5	Garage / Parking	3,138	2,567	571	81.8%
6	Extension (General)	684	557	127	81.4%
7	Conservatory	317	258	59	81.4%
8	Loft Conversion	88	71	17	80.7%
9	Outbuilding	974	770	204	79.1%
10	New Build	139	110	29	79.1%
11	Rear Extension	4,812	3,762	1,050	78.2%
12	Dormer	2,458	1,901	557	77.3%
13	Front Extension	1,029	793	236	77.1%
14	HMO	155	119	36	76.8%
15	Hip-to-Gable Conversion	20	15	5	75.0%
16	Side Extension	2,430	1,815	615	74.7%
17	Annex	54	23	31	42.6%

See how this applies to your postcode →

These are council averages. Your property is specific.

A flat conversion application has a 92.2% approval rate. Annex? Just 42.6%.
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What the data tells us

The range is massive: 42.6% to 92.2%. 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

2,440 planning applications in Harrow have been refused since 2020. Many of those homeowners had already paid for drawings and application fees. A £79 report shows you what gets approved — and what gets refused — near your property.

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More Harrow planning data

Nearby councils project type rankings

Methodology: Classifies 12,600 decisions in Harrow 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 Harrow Council's public planning portal, January 2020 to present. Full methodology →