Building Control in London: A Survival Guide (2026)

What is building control, and how is it different from planning?

Planning permission and building control answer two different questions. Planning asks whether a development is acceptable in its place — its size, appearance and impact on neighbours. Building control asks whether the construction meets the Building Regulations: is the structure adequate, is it insulated to current standards, is fire escape safe, is drainage correct? You can have planning permission and still fail building control, and vice versa. Most domestic projects need both, obtained separately.

The practical consequence is that a beautiful set of planning drawings does not authorise you to build. Planning drawings show the shape, size and appearance of the extension; they say almost nothing about the foundation depth, the insulation build-up, the steel that holds up the wall you removed, or how a fire would escape from the new loft room. All of that lives in a separate set of building-regulations drawings, checked by a separate body under a separate fee. Homeowners who budget for one and forget the other are the ones who stall on site — approved to build in principle, but with nothing a builder or inspector can actually work from.

Full Plans or Building Notice — which should I use?

There are two ways to get building-control approval for domestic work. Under Full Plans you submit detailed drawings and calculations for approval before work starts, and receive a formal decision. Under a Building Notice you give the council 48 hours' notice and build without approved plans, with everything checked on site. For anything structural — extensions, loft conversions, removing walls — Full Plans is the safer route: an error found on a drawing costs an eraser, the same error found when the steel is in costs a rebuild. Building Notice suits only small, simple, non-structural jobs.

• Full Plans — drawings and structural calculations approved before you start; fewer surprises, and your builder prices a fixed specification
• Building Notice — no approved plans, everything judged on site; only sensible for minor non-structural work
• Lenders, buyers and party-wall surveyors generally prefer the paper trail Full Plans produces

Which building control inspections will I need?

The inspector visits at defined stages and signs the work off only if each stage complies. Missing a stage — pouring foundations before they are inspected, for example — can mean opening the work back up. Knowing the sequence lets you and your builder book inspections in advance rather than holding up the site.

• Foundations / excavation — before concrete is poured
• Damp-proof course and oversite — before the floor is laid
• Drainage — before backfilling, and often an air/water test
• Structural elements — steel beams and connections in place
• Insulation and vapour barriers — before they are covered up
• Completion — final inspection issuing the completion certificate

What do the Building Regulations actually cover?

The regulations are organised into parts, each covering a discipline. For a typical London extension or loft conversion the parts most in play are structure (Part A), fire safety and means of escape (Part B — critical for loft conversions, which usually need a protected stair and mains-linked alarms), resistance to moisture (Part C), drainage (Part H), and the conservation of fuel and power (Part L, which sets insulation and energy standards). Good building-regs drawings specify how each relevant part is satisfied, so the inspector is confirming a documented solution rather than improvising one.

Several other parts routinely apply too: Part K governs stairs, guarding and protection from falling — directly relevant to a new loft staircase; Part F covers ventilation, which pairs with the ever-tighter insulation demands of Part L to prevent condensation and mould; and Part M can apply to access. Standards under Part L in particular have ratcheted up in recent years, so an extension today needs far more insulation and better-performing glazing than one built a decade ago. A drawing set that quietly works to old standards will fail inspection, which is why current, properly-specified building-regs drawings are worth paying for rather than reusing an old template.

Who actually inspects the work, and how do I choose?

Building control in England can be carried out by two kinds of body, and homeowners are often unaware they have a choice. The first is the local authority's own building control department. The second is a private-sector Registered Building Control Approver (the term that replaced Approved Inspector under the reforms following the Building Safety Act). Both do the same statutory job — checking your project against the Building Regulations and issuing a completion certificate — but they differ in how they work, and the drawings you submit are what make either of them efficient.

For a straightforward domestic extension or loft conversion the practical difference is modest; what matters far more is that the work is registered with one of them before it starts and inspected at the right stages. The reforms have tightened record-keeping and competence requirements across the board, so the days of informal, undocumented sign-off are gone. Good building-regulations drawings are the currency of both routes, because they let the inspector confirm a documented solution rather than improvise one on a muddy site.

Why does the completion certificate matter so much?

The completion certificate is the council's confirmation that the finished work complies with the Building Regulations. It is not a formality: when you sell, the buyer's solicitor will ask for it, and its absence can delay or derail a sale, force an indemnity policy, or require regularisation of the work after the fact. Insist that your project runs formally through building control from the start and that the completion certificate is issued and filed — it is the cheapest insurance you will ever buy on the project.

Regularisation — applying retrospectively to certify work that was never inspected — is possible but painful. The inspector may require parts of the finished building to be opened up so hidden elements like foundations and insulation can be checked, and there is no guarantee older work meets current standards. Getting the certificate at the time, off the back of approved Full Plans drawings, avoids all of that and leaves a clean paper trail that protects the value of the home.