Permitted development and building regulations compared

Permitted development and building regulations are two separate approvals with different tests, different decision makers and different consequences for getting them wrong. Permitted development under the GPDO 2015 asks whether the works need planning permission. The Building Regulations 2010 ask whether the construction meets technical standards. An extension can be permitted development and still be unlawful for want of building control, and it can have planning permission and still fail building regulations.

Almost every domestic extension needs building regulations approval. Rather fewer need planning permission. Owners routinely get that the wrong way round.

Two separate systems with different tests

Planning regulates land use, scale, siting and effect on other people. Its questions are about depth, height, position relative to the boundary, whether the house has been extended before, and whether the site is in a conservation area or subject to an Article 4 direction.

Building control regulates the building itself. Its questions are about the depth of the foundation, the U-value of the roof, the position of the damp-proof course, whether the stair has enough headroom, whether there is an escape window from the loft room, and where the rainwater goes.

They have no overlap in test and no overlap in enforcement. A planning officer does not check insulation. A building control body does not care whether the extension overshadows next door.

What building regulations control

The regulations are grouped into parts, each with an Approved Document giving practical guidance on how to meet them. For a domestic extension the ones that actually bite are: Part A structure, Part B fire safety, Part C site preparation and resistance to moisture, Part F ventilation, Part H drainage and waste disposal, Part K protection from falling, Part L conservation of fuel and power, Part M access, and Part P electrical safety.

Part L is the one that has moved most. The 2021 uplift raised fabric standards for extensions as well as new dwellings, and it applies to replacement thermal elements too, so replacing a roof on an existing rear outrigger brings the insulation standard with it.

Part O on overheating applies to new dwellings rather than extensions, which catches out anyone converting an outbuilding into a separate unit. So does Part S on electric vehicle charging infrastructure. The moment the project creates a new dwelling rather than extending an existing one, several additional parts come into play.

Approved documents relevant to extensions

Three technical points cause most of the refusals to issue a completion certificate.

Foundations near trees and drains. Part C and Part A together push depths well beyond the 900 mm people assume, particularly on shrinkable clay near mature trees, and the depth is decided on site by the inspector, not on the drawing.

Escape and fire separation where a loft is involved. A habitable room in the roof needs an escape window of the right size and position, or a protected stair, and the ceiling below often needs upgrading. Applicants discover this after the joists are in.

Drainage. Building over or near a public sewer needs the water undertaker's agreement under a build-over process which is separate from both planning and building control, and the undertaker can require diversion. Check the sewer records before you set the extension out.

Building notice against full plans

Two routes exist for domestic work, and the choice matters more than people think.

A building notice is short. You give notice at least two days before starting, no plans are checked, and no approval is issued. Compliance is judged by inspection as the work proceeds, which means a problem found on site is your problem to fix at that point.

Full plans means depositing drawings and calculations for checking, and receiving a decision notice. It costs more up front and takes longer, and it gives you something in writing before the concrete goes in. On anything structurally awkward, on any work involving a steel frame, and on all non-domestic work, full plans is the sensible route.

You can also use a registered building control approver instead of the local authority. Since the Building Safety Act 2022 reforms, approved inspectors became registered building control approvers and individual inspectors have to be registered, so check the registration before appointing. Higher-risk buildings, broadly those at 18 m or seven storeys and above, go through the Building Safety Regulator's gateway regime rather than ordinary building control.

Completion certificates and why they matter

The completion certificate is the document a purchaser's solicitor asks for, and its absence is the most common building regulations problem encountered on sale. Missing certificates are dealt with by indemnity insurance, a retention, or a regularisation application, and none of those are pleasant at exchange.

Where work was done without any notice at all, a regularisation certificate can be applied for retrospectively, which involves opening up work for inspection. Where the local authority wants to act, it may serve a notice under section 36 of the Building Act 1984 requiring the work to be altered or removed, and that power is time limited to twelve months from completion of the work.

Keep the certificate with the deeds along with any electrical and gas certificates. Photograph foundations and insulation before they are covered.

Party wall procedure sitting alongside

A third regime runs in parallel and belongs to neither. The Party Wall etc. Act 1996 governs your right to build on or near the boundary and your neighbour's protection, and the notice periods run to one or two months depending on the works.

Nobody tells you about it. The council does not enforce it, building control does not ask about it, and the first most owners hear of it is a letter from the neighbour's surveyor after the digger arrives.

Three approvals, three timetables. Draw them on one sheet before you commit to a start date.

Sequencing both for a small project

1. Check the permitted development limits for the class in question, including whether the house has already been extended and whether rights have been removed by condition or by an Article 4 direction.
2. If the works are outside the limits, apply for planning permission. If inside, consider a certificate of lawfulness for proposed development, which is the only formal confirmation available.
3. Settle the structural design and the drainage strategy, including any build-over agreement with the water undertaker.
4. Decide between a building notice and full plans, and deposit or notify accordingly.
5. Serve party wall notices once the excavation depths and boundary works are fixed.
6. Start on site, keep the inspection record, and collect the completion certificate at the end.

Where the works involve exterior finishes or plant, the planning position is narrower than people expect and worth checking separately, as set out in painting a house exterior and the permitted development limits and in domestic solar panels and the 200 mm projection limit. Conversion projects add the structural condition question covered in the Class Q structural works test.

Where an application is needed, the planning statement should address the design guide tests directly, and the report index shows what else a householder application may require.

PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval.

This is general guidance, not legal advice; check the position with your local planning authority or a qualified professional before relying on it. A lawful development certificate is the only formal way to confirm that works are lawful.