Your builder pours the foundation concrete tomorrow morning. Do you need to call building control first, or can they inspect it afterwards? Get this wrong and you’ll be digging it all back up.

Most homeowners have no idea when building control needs to be notified during their extension. They rely completely on builders to handle it. Then the completion certificate gets delayed because critical inspections were missed, and suddenly your house sale is falling through.

Based on 2025 UK building control procedures and our experience from hundreds of extension projects across Mansfield, Nottinghamshire, South Yorkshire, and Derbyshire, here’s exactly when inspections happen and what you need to know.

Key Topics Covered

  • The 6-7 mandatory inspection stages for typical extensions
  • When to notify building control (24-48 hours advance notice required)
  • What happens if you miss an inspection or fail one
  • Timing: when inspections actually happen during your build
  • The final completion certificate and why it matters
  • Who’s responsible for booking inspections (you or your builder)
  • Common inspection failures and how to avoid them

How Many Inspections Will Happen?

For a typical 25m² single-storey extension, expect 4-6 building control site visits. Double-storey or more complex builds require 6-8 visits, and loft conversions typically need 4-5. None of these are optional. Every stage must be completed before you can receive your completion certificate.

The Mandatory Inspection Stages

Stage 1: Commencement

Before any construction begins, building control need at least 24-48 hours’ notice. On this first visit, the officer checks site set-up, confirms the work matches approved plans, and agrees the inspection schedule with your builder. It sets the tone for everything that follows.

Stage 2: Foundation Excavation

This is the most time-critical inspection of the entire build. Once concrete is poured, nobody can inspect what’s underneath. Building control must visit after the trenches are dug but before a drop of concrete goes in. They check excavation depth against structural engineer specifications, assess ground conditions, verify trench dimensions, and look for tree roots, services, or signs of instability. Miss this inspection and you could be breaking up freshly poured concrete at a cost of £2,000-£5,000.

Stage 3: Foundation Concrete and DPC

After the concrete has cured and walls have been built up to damp proof course level, building control return to check the foundation depth and specification, confirm the DPC is installed correctly, and verify it sits at the minimum 150mm above ground level. Notify them when walls reach DPC height, before building any higher.

Stage 4: Oversite and Floor Construction

Before the floor slab is poured or any floor construction is covered, building control need to inspect the hardcore and sub-base preparation, the damp proof membrane, floor insulation thickness against Part L regulations, and underfloor ventilation. If your project sits in a radon-affected area, which includes parts of Mansfield, Nottinghamshire, and Derbyshire, they will also check radon barriers at this stage.

Stage 5: Drainage

Once new drainage is laid but before the trenches are backfilled, building control inspect pipe materials and gradient, connections to the main sewer, access chamber positions, and bedding materials. A drain test, either air or water, is also required and often witnessed by the officer directly. Drainage problems found after backfilling cost £3,000-£8,000 to excavate and reinstate. Get it inspected while it is still accessible.

Stage 6: Structural Elements

When the roof structure is up and any steel beams are installed, but before insulation or plasterboard goes in, building control check that structural steel matches the engineer’s calculations, that beams sit on proper padstones with correct bearings, that roof timbers and floor joists meet specification, and that wall ties and restraint straps are in place.

Stage 7: Insulation and Pre-Plaster

Once insulation is fitted but before it is covered, building control verify wall, roof, and floor insulation thicknesses against current Part L standards, check cavity barriers and fire stopping, and inspect ventilation provision. The 2022 energy regulation changes significantly raised the bar here, and building control scrutinise this stage closely.

Stage 8: Final Completion

When all work is finished, building control carry out a final inspection covering fire safety measures, means of escape, ventilation systems, safety glazing, staircases and handrails, drainage, electrical and plumbing certification, and overall energy performance. Only after this visit, with everything in order, is the completion certificate issued.

Who Books the Inspections?

Your builder should handle all notifications on your behalf, but the legal responsibility sits with you as the property owner. Agree at the outset that your builder will book each stage and ask for confirmation every time one is scheduled. Most councils offer online or app-based booking and can accommodate same-day visits if you call before 10am, though 24-48 hours’ notice is always preferable.

The Completion Certificate: Why It Matters

Without a completion certificate, selling your property becomes significantly harder. Solicitors request building control certificates for all extension work as standard, and buyers will either pull out or reduce their offer by £5,000-£15,000 if one is missing. Lenders can reject remortgage applications on the same basis, and some insurers will not cover extensions that lack proper certification. Keep the certificate permanently alongside your property deeds.

The Rosebrick Approach

At Rosebrick Developments, we manage every inspection stage as standard. We book 48 hours ahead without exception, coordinate concrete deliveries and site progress around confirmed inspection slots, and build to regulations the first time so there are no failures and no rework. You receive copies of every inspection confirmation, and we stay involved until the completion certificate is in your hands.

Building control is not bureaucracy. It is proof that your extension is safe, compliant, and will not cause problems further down the line.

Planning an extension in Mansfield, Nottinghamshire, South Yorkshire, or Derbyshire? Contact Rosebrick Developments today.