Planning Permission for a London Extension: Timing, Refusals and Permitted Development

The most expensive assumption in a London renovation is a date. A homeowner is told the council will decide in eight weeks, books the builder for week nine, and finds that the eight weeks were only the middle of the process. This post is about what actually sits either side of that decision, and what to do when the answer is no.

It is written from the questions clients put to NU every week, and from the way we take a scheme from first call to consent.

Do you need planning permission at all?

It depends on the property, the proposed work and the existing restrictions. Some work may be permitted development, but eligibility should be checked for the actual building before relying on that route. Householder permitted development rights do not apply to flats and maisonettes in the same way as houses, and prior alterations and restrictions matter.

An Article 4 direction can remove specified permitted development rights within its defined scope. Check the actual direction and the actual property rather than assuming every restriction is the same. Where you want certainty that work is lawful, a lawful development certificate is the formal route. It is different from building regulations approval and should reflect the exact proposal.

A decision date is not a start date

Allow for surveys, design and validation before the authority's assessment period even begins. Requests for information, consultation and revisions can extend the overall timeline, so never treat an indicative decision date as a guaranteed site start.

And consent is not the finish line either. Read the decision notice for conditions, and check the other approvals and agreements the works need. Building control, structural calculations, the party wall process and, where a public sewer is close, Thames Water agreement all sit alongside planning. Design, technical and contractual readiness remain separate questions from the permission itself.

Everything starts with design. If you go straight to build costs or programme before the scope exists, the contractor cannot price the project properly and every number stays provisional. Design first, then scope, then cost certainty.

Pre-application advice, and what it is not

Pre-application advice can be useful where policy, heritage, scale or neighbour effects are uncertain. Its value depends on the question asked and the information supplied. It is not planning permission. No responsible project team can guarantee a council's decision. Good preparation identifies the policy issues and improves what is submitted, but the decision stays with the authority.

If planning is refused

Refusal is not the end of the project. Review the reasons with the designer or planning consultant before choosing a route. There are three: a revision, a new application, or an appeal. The strongest route depends on the specific refusal and the practical brief, not on which one feels quickest.

Neighbour objections are not an automatic refusal. The authority assesses the application against the relevant planning considerations. A proposal should address neighbour effects properly, without assuming that either support or an objection decides the outcome.

If you later want to change the approved design, changes should be checked against the approved documents and conditions before implementation. Get the route for the amendment confirmed rather than building it and hoping. The costs of the extension itself are set out in rear extension cost in London and loft conversion costs in London.

How NU handles it

NU is a design and build contractor in Fulham. Architecture, interior design, project management and construction under one contract, with planning permissions handled in house and structural engineers and party wall surveyors coordinated as part of the job. We work through a twelve step process from the first call to handover, so the planning stage is one step in a sequence rather than a hurdle you clear alone.

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Thinking about this on your own house? Fill out the contact form or call 020 7731 6841 and let's get you booked in for a free call with Nick.