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Two Separate Approvals, One Common Confusion

Most homeowners treat planning permission as the finish line. It isn't. Planning permission is about how development affects neighbours, the street scene and the wider area. Building Regulations are about how the finished work actually performs — whether it stands up, keeps fire contained, ventilates properly and holds on to its heat. You may need one, both, or neither. A modest internal rejig may need neither; a two-storey rear extension almost always needs both. A loft conversion often sits comfortably outside planning but very much inside the regulations.

In England and Wales the rules sit under the Building Regulations 2010, supported by a set of Approved Documents lettered A to S. Scotland and Northern Ireland have their own equivalents, similar in spirit and intent. Crucially, the regulations don't just cover new structures. They apply to building work, which is a far broader term than most people expect — material alterations, changes of use, and the replacement of certain fittings such as windows, doors and heating appliances all fall within scope.

Who Checks It, and How You Prove It

Compliance is verified by a building control body: either your local authority's building control team or a private registered inspector. You have two main application routes for domestic work.

• Full Plans application — you submit drawings and specifications up front and receive a decision, normally within five weeks (or eight if you agree an extension). This is the safer route for extensions, loft conversions and anything structural, because problems are spotted on paper rather than on site.
• Building Notice — less paperwork, no formal plan approval, but you carry more risk. It suits simple jobs like a straightforward bathroom or a like-for-like window swap, and it is generally not accepted for work near a public drain or in a commercial building.

Certain trades — gas, some electrical work, replacement glazing — can be self-certified by a competent person scheme, which means you receive a certificate instead of a building control visit. For anything else, the golden document at the end is the Completion Certificate. Keep it forever. Solicitors will ask for it when you sell, and mortgage lenders can refuse to lend against works with no evidence of approval. If previous owners built without approval, a Regularisation Certificate is the retrospective route, though it involves opening up work so it can be inspected.

Part A: Structure — the Bit That Holds Everything Up

Part A governs structural stability. In practice, this is where most domestic projects run into trouble, because removing a wall is rarely as simple as it looks on a Saturday morning.

• Any load-bearing wall removal needs a structural engineer's calculations and a suitable beam — often steel, sometimes timber or a proprietary lintel. Bearings matter: allow at least 150mm of end bearing for masonry lintels and typically 100mm onto padstones for steel beams, unless the engineer specifies otherwise.
• New openings in walls should be kept to a sensible width and kept clear of existing piers and returns, which carry load down to the foundations.
• Wall ties in new cavity walls are usually spaced at around 900mm horizontally by 450mm vertically, with tighter spacing around openings. Get this wrong and you get water tracking and eventual movement.
• Foundations must reach suitable ground. Clay soils, trees nearby, drains, made ground and old pits all change the design, sometimes requiring deeper trenches or a reinforced raft.
• Never cut roof trusses, notch floor joists beyond the permitted zones, or remove chimney breasts without advice — chimney breasts in particular often support the stack above.

Part B: Fire Safety and Escape Routes

Fire safety requirements scale with height. A two-storey house typically needs 30 minutes of fire resistance to structure and separating walls; a three-storey house, or a loft conversion creating a third storey, generally needs 60 minutes. Where an escape route passes through a habitable room or a garage, or where a loft conversion relies on an open-plan layout, the staircase often needs to be enclosed with FD30 doors — 30-minute fire doors with intumescent strips and cold smoke seals, plus a self-closer.

Alarms must be mains-powered and interlinked: a smoke alarm on each storey and in circulation spaces, a heat alarm in the kitchen. Stair balustrades must resist a 100mm sphere, so you cannot have gaps a child could squeeze through, and guarding should be at least 900mm high internally and 1100mm where a window sits close to the floor.

Parts F and L: Ventilation and Energy Performance

As homes become more airtight, ventilation becomes a design decision rather than an afterthought. Part F expects background ventilators — trickle vents or equivalent — plus extract in kitchens, bathrooms and utility rooms. Rough intermittent rates are 30 litres per second in a kitchen, 15 in a bathroom and 60 above a hob. Whole-house systems such as mechanical ventilation with heat recovery suit very airtight new builds.

Part L sets the energy targets, and the honest headline is this: fabric first. Insulate to a good standard, make the insulation continuous, and seal the junctions where walls meet roofs and floors — thermal bridges are where heat quietly escapes. Typical target U-values are around 0.18 W/m²K for walls and 0.13 for floors, with windows in the 1.2 to 1.4 range. Any extension with a floor area over 30m² that is not separated by external quality doors must meet full energy standards, and re-roofing or rendering can count as a thermal element and trigger the requirement to upgrade insulation.

Practical Steps Before You Start

• Talk to building control early — a free pre-application conversation saves money later.
• Appoint a structural engineer before you buy a beam, not after.
• Check whether a conservatory is exempt: under 30m², at ground level, separated by external quality doors, glazing compliant, and no radiator removed.
• Budget for fees, typically a few hundred pounds for domestic work, and remember inspections must be booked in at key stages before work is covered up.
• Keep drawings, calculations, photographs and certificates together — your Completion Certificate is worth as much as the finished room.