What you gain
Without a certificate, the project may still be lawful if it meets the relevant permitted development rules. The certificate's purpose is to establish the planning position formally rather than leave a later owner or decision-maker to reconstruct the assessment from scratch. Planning Portal guidance specifically identifies its usefulness when a property is sold. [3][1]
The benefit is especially relevant where the claim depends on identifying original walls, accounting for previous additions or interpreting a restriction. These are matters which require evidence, not simply confidence that the extension is “within permitted development”. [4][2]
A certificate also gives the project a defined set of described works and referenced drawings. Those documents provide a clear basis for checking whether the proposed construction still matches the planning assessment. [2]
What it does not buy
A certificate does not make an oversized or otherwise ineligible project permitted development. The council must be satisfied about lawfulness, and a certificate application is not a way to obtain planning permission on design merits. [5][2]
It does not cover a different scheme built later, establish structural adequacy or settle a lease or boundary dispute. Building regulations and private rights are separate. Any required prior-approval procedure also remains necessary. [2][6]
Do not treat a proposed certificate as permanent protection against every later legal change. The statutory effect is qualified where a material change relevant to lawfulness occurs before work begins. A long-delayed start may therefore need a fresh check. [5]
What does the application cost?
From 1 April 2026, the ordinary national planning fee for enlarging or altering a single dwellinghouse is £548. A certificate for proposed operations normally attracts half the equivalent planning application fee. For a straightforward proposed house extension in that category, the calculation is therefore £548 ÷ 2 = £274, before considering any applicable exemption or concession. This is not the fee for every type of certificate. [7][8]
Budget separately for the statutory fee and the professional work needed to prepare the drawings and evidence. Ask for a quotation covering the preparation your project requires.
Planning fee reform is proposed with 8 December 2026 recorded as the intended commencement date. Obtain the operative certificate fee for your submission date from the final schedule. The existing annual-indexation mechanism also requires a fresh figure check for 1 April 2027. [9][10][8]
Decide by the uncertainty, not just the form
Ask what would otherwise remain unresolved: the original building, the drawings, a planning condition or proof of the complete permitted development test. If the required facts cannot yet be established, improve that evidence before assuming that paying a certificate fee will remove the uncertainty. [2]
Keep the certificate, its plans and the supporting assessment with the property records. Also keep the separate building control documents. Together they answer different questions; neither should be presented as a substitute for the other. [2][11]