Planning permission and building regulations are not the same thing.

Planning permission: may you build it?

Planning is the local planning authority's decision on whether a development is acceptable in its place: its size, its height, its appearance, its effect on neighbours and the street, and the use the building is put to. Many domestic projects fall under permitted development and need no application, subject to the limits described in planning permission for an extension. Everything else needs an application, and a listed building needs listed building consent as well. Where no application is needed, a lawful development certificate puts that in writing.

Building regulations: how must it be built?

Building regulations are national standards for the construction itself, set out in the Approved Documents. They cover the structure, fire safety, resistance to moisture, sound, ventilation, drainage, heat-producing appliances, stairs and guarding, energy efficiency, access, glazing and electrical safety. They apply whether or not planning permission was needed. An extension that is permitted development still needs building regulations approval; so does a loft conversion, a structural opening, a new bathroom that changes the drainage, and most electrical work in a kitchen or bathroom.

You choose who checks the work: the local authority's building control department, or a private registered building control approver. Both inspect at stages and both issue the completion certificate.

Two routes to approval

• Full plans. Detailed drawings and calculations are submitted and checked before work starts. You can expect a decision within five weeks, or two months if you consent to the longer period. Once the work is finished and inspected, the completion certificate usually follows within eight weeks. This is the route for anything with structure in it.
• Building notice. A short notice of the intention to carry out work; you may start two days after it is submitted. Nothing is checked in advance, so mistakes are found on site by the inspector. It is only for smaller projects.

The parts that decide the drawings

For an extension, a loft or a refurbishment, a handful of the Approved Documents do most of the work. Part A, structure: the beams, the foundations, the openings. Part B, fire: escape routes, fire doors, alarms, and the 4.5 metre rule that turns a loft stair into a protected route. Part C, moisture and ground: damp-proof courses and membranes. Part F, ventilation: extract in kitchens and bathrooms, background ventilation elsewhere. Part K, stairs and guarding. Part P, electrical safety, usually met by using a registered competent person who self-certifies the work. And Part L, energy.

Part L sets limiting U-values for new elements added to an existing house. Under the 2021 edition of Approved Document L, which has applied since 2022, a new wall in an extension must achieve 0.18 W/m²K, a new roof 0.15, a new floor 0.18, and new windows 1.4. Those numbers decide the wall build-up, the insulation depth and the glazing specification before the room is drawn in any detail.

The order they run in

1. The permitted development check, or the planning application. Nothing else is worth spending on until the planning question is settled.
2. The building regulations drawings and structural calculations, submitted as full plans.
3. The party wall notices where the work touches a boundary, timed so that the notice periods end before the start on site.
4. The build, with the inspections at each stage.
5. The completion certificate, which goes in the file with the drawings and the finishes schedule. A buyer's solicitor will ask for it.

One set of drawings

On a design and build contract the same team draws for planning, for building control and for the price, so the drawings that get approval are the drawings that get built. That is the point of the model, and it is why the studio's process puts the drawings before the price. The building regulations that matter most under a roof are set out in loft conversion types and rules.