How Long Does Planning Permission Take for an Extension? The Real Timeline
- Jun 9
- 3 min read
You've designed the extension and you're ready to submit. The next question is how long the council will take to come back. Long enough to plan the build? Long enough to start ordering materials?
We're a Kettering-based team that designs and builds house extensions in Kettering and across Northamptonshire. We handle the planning application as part of every project. Here's the realistic answer: the statutory timeline is 8 weeks from validation, but the path from "we'd like to extend" to "permission granted" usually runs longer.
How long does planning permission take for an extension?
The statutory determination period for a householder extension application is 8 weeks from the date of validation. The council has to issue a decision within that window. Larger or more complex extensions can run to 13 weeks. Validation itself takes a few days to a couple of weeks before the 8-week clock starts ticking.
What happens during those 8 weeks
Once your application is submitted via the Planning Portal, the council validates it. They check the application is complete, the fee has been paid, and the supporting drawings meet their requirements. Once validated, the formal 8-week determination period begins.
The first three weeks are the public consultation. The application goes online, neighbours are notified, and they have three weeks to submit comments or objections. Local interest groups, conservation officers and councillors may also be consulted at this stage.
Weeks 3 to 7 are the internal assessment. A case officer reviews your drawings against local planning policy, considers any comments received, visits the site, and forms a view. Larger or contested applications may go to a planning committee for the final decision.
The decision usually arrives in the final week of the 8. Approval, refusal, or a request from the council to extend the determination period in writing.
When the process takes longer than 8 weeks
The 8-week figure is the standard. In practice, several things push it out:
Conservation areas and listed buildings. Additional consents sit alongside the planning application, with their own consultation periods.
Larger or more complex applications. A two storey extension with significant impact on neighbours can take 13 weeks. Anything requiring an Environmental Impact Assessment can take 16 weeks.
High volume of objections. If a planning committee has to determine the application rather than the case officer, this can add weeks.
Incomplete application. If the council asks for additional drawings, reports or surveys after validation, the clock keeps ticking while you scramble to provide them.
Slow validation. Submitting in December, August, or with missing documents can mean a fortnight or more lost before the 8-week period even begins.
Local authority backlog. Most councils meet the statutory deadline, but where workload is heavy the council will ask in writing for your consent to extend. It's usually better to agree.
Local councils, local timelines
Most extensions in Northamptonshire fall under one of two unitary authorities: North Northamptonshire Council (covering Kettering, Corby, Wellingborough and the surrounding towns) or West Northamptonshire Council (covering Northampton, Daventry, Towcester and Brackley). Both publish their planning determination statistics, and both are broadly in line with the 8-week statutory target, with some seasonal variation.
When to submit your application
Working backwards from when you want construction to start, allow:
2 to 3 months for measured survey and design before submission
1 to 2 weeks for validation
8 weeks statutory determination (or 13 for complex applications)
2 to 4 weeks to discharge any pre-start planning conditions after approval
That's 4 to 6 months total from first design meeting to being able to start work on site. For a build that needs to be finished by a specific date (a baby on the way, a wedding, end of the school summer holidays), submitting at least six months ahead is sensible.
Get a quote for an extension in Northamptonshire
If you're planning a house extension in Corby or anywhere else in Northamptonshire, speak to our team. We handle the design, drawings and planning submission as part of every project, so you don't have to chase the council yourself. Finance is available through Phoenix Financial Consultants if you'd rather spread the cost.
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