Building regulations: what they cover and why they matter

Planning permission and building regulations approval are two entirely separate processes that get confused constantly, and a project can clear one without automatically clearing the other. Planning permission is about whether a building can go where it's proposed; building regulations are about whether, once built, it's actually safe and performs properly.

Building regulations set minimum standards across a defined set of technical areas, referred to as "Parts." Part A covers structural safety, including foundations, loadbearing walls and lintels above openings. Part B covers fire safety, including escape routes and interlinked smoke alarms. Part L covers energy efficiency, setting minimum thermal performance, U-values, for walls, roofs, floors and glazing. Part P covers electrical safety, requiring new circuits and consumer unit work in most rooms to be certified by a registered electrician. Almost every extension or loft conversion touches several of these Parts at once, which is why building regulations approval applies even to projects that don't need planning permission at all.

Approval can be sought via two routes, and it's worth understanding which one a builder is proposing to use. A "full plans" application involves submitting detailed technical drawings for checking before work starts, with a decision typically given within five weeks, or up to two months with consent, and an approval that stays valid for three years if work hasn't yet begun. A "building notice," more commonly used for smaller domestic projects, lets work start just two days after the notice is submitted, with a building control inspector checking compliance as the work proceeds rather than approving detailed plans upfront; it's faster to get moving but doesn't give the same formal advance sign-off on the design itself.

Whichever route is used, mandatory inspections happen at defined stages of the build, commonly including foundation excavation, damp-proofing, structural work such as steelwork or new loadbearing elements, and final completion. These aren't a formality to be scheduled around; an inspector needs to physically see certain elements, like foundations or drainage, before they're covered up by the next stage of work, so a builder skipping or rushing past a scheduled inspection point is a genuine problem, not just an inconvenience.

Once work is finished and has passed its final inspection, the local authority is required to issue a completion certificate, and rule changes from December 2012 mean this should happen automatically, commonly within around eight weeks, without needing to be specifically requested. It's worth confirming a completion certificate has actually arrived at the end of a project rather than assuming it has, since it's the document that proves, on paper, that the finished work meets building regulations.

Skipping building regulations approval altogether, whether deliberately to save cost or through an oversight by an inexperienced builder, carries consequences that often don't surface until years later. Local authorities retain enforcement powers even after a property has changed hands, and can require corrective work, or in extreme cases removal of the work, if non-compliance is found. In practice, unapproved work most commonly surfaces during conveyancing when selling, where a buyer's solicitor or surveyor flags the missing paperwork; at that point a mortgage lender may refuse to lend against the property or lend a reduced amount, and it can affect the validity of home insurance too. Two partial fixes exist at that stage, a retrospective "regularisation" application to Building Control, or indemnity insurance that protects against enforcement action rather than proving compliance, but both cost money and neither is guaranteed to fully satisfy a cautious lender or buyer.

Building control fees are a genuine, if often overlooked, line item on top of the build cost itself, and they vary by local authority and by which route is used. For a typical single-storey extension, fees commonly run around £260-£360 as a plan charge plus roughly £160 for inspections under full plans, or £450-£800 under a building notice; a loft conversion is commonly similar, around £260-£360 plus £160, or £430-£510 under a building notice. One partial exception is worth knowing about: a trade registered with a Competent Person Scheme, most commonly used for electrical work under Part P or gas work, can self-certify that specific element of the job, notifying the local authority directly, without a separate building control fee applying to that part of the project, though the rest of the build still needs its own approval route.

None of this means every homeowner needs to personally understand the full technical detail of Parts A through P before starting a project. It does mean checking, before work starts, that a builder or architect has actually submitted the relevant building regulations application through one of the two routes, rather than assuming it's been dealt with, since it's considerably cheaper and less stressful to confirm this at the outset than to discover years later, mid-sale, that it was never done.

Frequently asked questions