Planning permission in Hillingdon isn't a simple yes or no — and most homeowners don't realise that until it's too late. The rules that apply to your neighbour's extension might not apply to yours, even if you live next door. WhatCanIBuild exists precisely because untangling that complexity for your specific address is harder than it looks.
The short version
- Whether you need planning permission depends on your specific property, not just the type of project
- Hillingdon has 31 conservation areas, significant Green Belt land, and Heathrow Airport policies that can change everything
- The best way to know for sure is to check what applies to your exact address
Hillingdon isn't one place — it's dozens
Hillingdon stretches from Heathrow to Harefield, taking in Hayes, Uxbridge, Ruislip, Northwood, and everything in between. That's a huge geographic and policy range. A homeowner in UB3 is dealing with a completely different set of local pressures than someone in HA6. And within each postcode, individual streets can sit inside conservation areas, Green Belt boundaries, or be subject to Article 4 directions — none of which show up when you google "do I need planning permission for an extension."
Most homeowners don't realise that where your property sits on a map — not just which borough you're in — determines which rules apply.
The exceptions are where people get caught
Even projects that would normally fall under permitted development — meaning no formal application required — can require permission in Hillingdon if your property is subject to restrictions most owners aren't even aware of. Conservation areas. Listed building status. Flood zones. Article 4 directions that remove permitted development rights from specific streets or property types. Green Belt constraints with their own separate logic.
Hillingdon has 31 conservation areas alone. That's 31 distinct zones where the normal rules may not apply, and where what got approved three streets away tells you almost nothing about what will happen with your project.
Heathrow proximity
Properties near Heathrow Airport may be subject to additional local plan policies around height, noise, and development that don't apply elsewhere in the borough. If you're in the western half of the borough, this is worth knowing about before you start planning anything.
Knowing you're in a conservation area isn't enough
This is where most people get stuck. They find out they're in a conservation area — or they don't, because they never checked — and they either assume everything is restricted or assume it's fine. Neither is right.
Being in a conservation area doesn't mean you can't extend or alter your home. It means that specific rules apply to specific project types, and the outcomes depend on what's been approved and refused nearby, how your property sits within the area's character, and how Hillingdon's planning officers have been interpreting applications on similar streets. That's not something a general guide can tell you. WhatCanIBuild shows you what's actually been approved and refused for projects like yours in your area — not just what the rules say in theory.
What your address actually tells you
The application fee for a householder planning application in Hillingdon is £258 and the typical decision time is 8 weeks. But none of that matters if you submit an application for something that was always going to be refused — or if you skip an application for something that genuinely required one.
The question isn't just "do I need permission." It's "given everything about my specific property and project, what are my actual chances — and what's tripped up similar projects nearby?" WhatCanIBuild gives you that picture: the constraints on your property, what's been approved on your street, and what your approval odds actually look like before you commit to anything.
These rules vary by property
Conservation areas, Article 4 directions, and other constraints can change everything. Check what actually applies to your address.
Check my address