What Building Control Inspects at Each Stage

Your builder will cover things up. That's their job. Concrete goes over foundations, soil goes over drains, plasterboard goes over insulation and wiring. Once something is covered, nobody can see it without ripping the building apart. The building control officer is the only independent person who checks that what's underneath is right, before it disappears.

Most homeowners treat building control as a bureaucratic hurdle. Something the builder handles. Something that happens in the background. That's a mistake. The BCO's inspections are the single most important quality gate on your entire project, and understanding what they check at each stage puts you in a position to spot problems your builder would prefer you didn't notice.

The BCO Is Not Your Builder's Friend

The building control officer enforces the Building Regulations. That's their entire job. They don't work for your builder, they don't care about your builder's programme, and they have no commercial incentive to let substandard work pass. The regulations they enforce exist to make buildings safe, structurally sound, energy efficient, and accessible. Which means the BCO's interests and your interests are almost perfectly aligned.

Your builder wants to get the job done. Efficiently. Profitably. That's not a criticism. Good builders care about their reputation and do solid work. But even good builders sometimes take shortcuts when they think nobody's looking. And bad builders rely on nobody looking. The BCO looks.

Here's what the BCO does not do: they don't check workmanship quality. A wonky brick course, uneven pointing, a slightly off-level wall, scratched window frames. None of that is a building regulations matter. The BCO checks that the building is structurally safe, thermally adequate, properly drained, and fire compliant. If your wall ties are the wrong material, the BCO catches it. If your brickwork is ugly, that's between you and your builder.

How Many Inspections to Expect

A single-storey extension typically involves seven building control inspection stages. Only two are legally required (commencement and completion), but the stages in between are where the real quality control happens. The exact number of site visits may vary by local authority, and BCOs sometimes combine adjacent stages, but the seven checkpoints below represent what a typical project goes through.

For a typical single-storey extension, the seven stages are:

1. Commencement (BCO visits when work starts to review the approved plans and agree the inspection schedule)
2. Foundation excavation (before concrete is poured)
3. Drainage (before pipes are backfilled)
4. Oversite and damp proofing (before the floor slab is poured)
5. Structure and Roof (steelwork, wall ties, cavity trays, lintels, roof frame)
6. Pre-plaster (insulation, first fix electrics, fire stopping, ventilation)
7. Completion (certificates collected, final walk-through)

Some BCOs combine stages where it makes sense for the project. Drainage and oversite, for example, are often inspected in a single visit. What matters is that nothing gets covered up before the relevant stage has been signed off.

15-30

A typical building control inspection visit. The BCO arrives, measures what they need to see, takes photographs, confirms whether you can proceed to the next stage, and leaves. Have the approved drawings on site.