Planning permission in Harrow is one of those topics where the more you dig, the less certain you feel. The rules that apply to your neighbour's house might not apply to yours — and most homeowners only discover that after they've already started work. WhatCanIBuild exists precisely for this moment: when you suspect the answer isn't simple, but you don't know where to start.
The short version
- Whether you need permission depends on your specific property, not just the project type
- Harrow has conservation areas, Article 4 directions, Green Belt land, and listed buildings — any of which can change the rules entirely
- The typical decision time is 8 weeks, with a householder application fee of £258
It's not just about what you're building
Most people approach this question the wrong way. They think about the project — an extension, a loft conversion, a new fence — and assume that's what determines whether they need permission. But in Harrow, where you're building matters just as much as what you're building.
Harrow has Green Belt land in the north, including around the Bentley Priory nature reserve. It has multiple conservation areas — Pinner, Stanmore, Canons Park — each with their own Article 4 directions. It has listed buildings and locally listed buildings scattered across the borough. Any one of these designations can strip away the freedoms that would otherwise apply to your property. The question isn't just "what am I building?" — it's "what constraints sit on my specific address?"
Worth knowing
Article 4 directions in Harrow's conservation areas remove certain permitted development rights that homeowners in other parts of the borough take for granted. If you're in or near Pinner, Stanmore, or Canons Park, your situation may be more restricted than you'd expect.
The things that catch homeowners off guard
Most homeowners don't realise how many invisible layers sit on their property. You might not be in a conservation area — but you might be in a locally defined area of special character. Your house might not be listed — but it might sit within the curtilage of one that is. Your garden project might seem minor — but if your property backs onto Green Belt land or a protected open space, the calculation changes entirely.
Harrow Council also has a Garden Land Supplementary Planning Document, a Tall Buildings SPD, a Residential Design SPD, and guidance on the loss of open space — each of which can influence how your application is assessed. These aren't edge cases. They affect ordinary homes on ordinary streets across HA1, HA2, HA3, HA5, and HA7.
And even if you're confident about your own property's designations, there's another layer: what's actually been approved and refused nearby. Knowing you're in a conservation area is one thing. Knowing what that actually means for your specific project type — whether similar extensions on your street got through, and why some didn't — is something else entirely. That's where WhatCanIBuild goes further than anything you'll find on a council website.
Before you assume, check
Guessing is risky. Getting it wrong means enforcement action, retrospective applications, or having to undo work you've already paid for. The feeling that your project is "probably fine" is exactly the moment to pause.
The best way to know where you stand is to check your specific address against everything that applies to it — not just the general rules, but the local designations, the approval patterns nearby, and the odds for your exact project type. WhatCanIBuild pulls all of that together for your property in seconds.
These rules vary by property
Conservation areas, Article 4 directions, and other constraints can change everything. Check what actually applies to your address.
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