Lawful Development Certificates for loft conversions

Permitted Development has one structural weakness: it is self-assessed. Nobody checks your volume calculation, nobody confirms your dormer clears the ridge, and nobody issues a document at the end. You build, and the question of whether you were entitled to sits unanswered.

It stays unanswered until you sell, when a buyer’s solicitor asks what authorised the third bedroom, and “the builder said we didn’t need planning” turns into a delayed exchange, a retention, or an indemnity policy that covers the buyer rather than resolving anything.

An LDC is a formal determination by the local planning authority that a described development is lawful — either as proposed (before you build) or as existing (after). See Lawful Development Certificates — Planning Practice Guidance.

Critically, it is a legal determination, not a planning decision. The council is not exercising judgement about whether your dormer is attractive or neighbourly. It is answering a question of law: does this scheme fall within the class or not? That makes the outcome predictable in a way a planning application never is — if your numbers comply, the certificate follows.

You can apply for a certificate for a proposed development or an existing one. Proposed is almost always the right choice.

• Proposed: decided on drawings. If the council reads Class B differently from you — on the eaves setback, on whether your end-of-terrace takes 40m³ or 50m³, on where the highway frontage runs — you find out while the design can still move.
• Existing: decided on what is built. If it breaches a condition, you now own an unlawful structure, and the routes out are a retrospective planning application or physically altering what you have built.

Even on the old figure it was a bad plan. The clock only starts on substantial completion, the burden of proving when that happened falls on you, and in the meantime you own a house that is harder to sell, harder to remortgage and harder to insure. Check the current position before relying on any of it — see Time limits for enforcement action — Planning Practice Guidance.

1. The application form and fee — for a proposed development, half the equivalent householder planning fee.
2. A location plan and block plan at standard scales, showing the property in context.
3. Existing and proposed drawings — plans, sections and elevations, dimensioned, showing the ridge line, the eaves line and the dormer setback.
4. A volume calculation demonstrating the added volume against the original roof and the applicable cap. This is the part applicants most often submit as an assertion rather than a working, and it is the part most likely to generate a query.
5. A short statement setting out which class you rely on and how each condition is met.

LoftNow’s report is built around this list. It shows the full volume working — every dimension and formula, lettered onto a 3D wireframe of your roof — plus plan, section and elevation drawings and the compliance position on each Class B condition. It is not a substitute for the architect’s drawings that accompany the application, and it is the evidence base the application is built from.

The statutory determination period is eight weeks, though straightforward householder certificates are frequently decided sooner. There is no consultation period and no neighbour notification, because there is nothing for anyone to object to — the council is answering a question of law, not canvassing opinion.