Permitted development rights allow certain kinds of extension and alteration to go ahead without a full planning application, provided the proposal fits within specific limits on size, height and position. The trouble is that 'permitted development' gets used loosely in conversation as though it's a blanket exemption, when it's actually a set of quite precise conditions that a scheme either meets or doesn't.
Genuinely confirming permitted development status, rather than assuming it, is a distinct piece of work that happens before a design is finalised.
Checking designation and removed rights first
The starting point is establishing whether the property sits in a conservation area, an Area of Outstanding Natural Beauty, or has had permitted development rights removed by an Article 4 direction or a condition on a past planning approval. Any of these narrow or remove the default rights, and none of them are visible just by looking at the house.
This check involves looking at the council's own records and, where relevant, the property's planning history and title, rather than relying on general assumptions about what's normally allowed.
Measuring the actual proposal against the specific limits
Permitted development limits cover things like the depth a single-storey rear extension can project, the maximum height at the eaves and ridge, how close to a boundary a structure can sit, and how much total volume has already been used by previous extensions. These figures are precise, and a scheme measured a small margin over a limit doesn't qualify partially — it either fits or it needs a full application.
This is where a scheme drawn up before checking the limits properly can come unstuck: a design that looks entirely reasonable can still exceed a specific height or depth threshold once it's actually measured against the rules rather than eyeballed.
Considering a lawful development certificate
Because permitted development relies on self-assessment against the rules, it's common — and sensible — to apply for a Lawful Development Certificate, which is a formal confirmation from the council that a specific proposal, as described in the application, does fall within the rights claimed. This isn't compulsory, but it provides a documented answer rather than an opinion.
A certificate application still takes drawings and a fee, and a decision period similar to a planning application, but it produces a piece of paper that settles the question rather than leaving it as an assumption.
Recording the evidence for the future
Whether or not a certificate is obtained, it's worth keeping a record of the measurements and reasoning used to conclude a scheme was permitted development — dated photographs of the property before works, the measurements taken, and the specific rule relied on. This becomes important at a future sale, when a solicitor or buyer's surveyor may ask for evidence that works were lawful.
Without a certificate or clear records, an otherwise lawful extension can become a source of delay or renegotiation during a future conveyancing process, even years after the work was completed.
Where this catches out extensions and loft conversions specifically
Loft conversions are a common place permitted development gets misapplied, because volume allowances, roof alteration limits and the treatment of dormer windows all have specific conditions attached, including restrictions on materials and side-facing windows needing to be obscure-glazed. Rear extensions are the other common area, with depth limits differing between detached, semi-detached and terraced houses.
Flats and maisonettes have far more limited permitted development rights than houses, and this distinction is sometimes missed by owners assuming the same general rules apply across all property types.
Common questions
Is a Lawful Development Certificate compulsory?+
No, but it's the only way to get a formal, documented confirmation from the council rather than relying on your own or a contractor's interpretation of the rules.
Does permitted development apply the same way to flats as houses?+
No. Flats and maisonettes have significantly more restricted permitted development rights than houses, and many alterations that would be automatic on a house need full planning permission on a flat.
What if I'm not sure whether a previous extension used up my allowance?+
Check the planning history held by the local authority and, where possible, the property's deeds. Volume used by any extension since the relevant reference date counts against the current allowance, regardless of who carried it out.
Have your permitted development claim checked properly
We can measure a proposed scheme against the actual limits and advise on whether a lawful development certificate is worth obtaining.