What Does a Building Control Inspector Actually Check?

You (or your builder) must notify building control before starting work and at each key stage. The inspector visits the site, checks the work, and either:

• Passes it — you can continue to the next stage
• Requests changes — something does not comply and needs to be corrected before the work can continue

The inspector is not there to catch you out. They are checking that the work is safe, structurally sound, and meets minimum standards. Most inspections take 15–30 minutes.

When: Before or just as work starts on site.

What they check: That building control has been properly notified, the site matches the plans (if Full Plans were submitted), and any obvious site constraints are noted.

This is sometimes a desk-based check rather than a site visit.

When: After trenches are dug, before concrete is poured.

What they check:

• Depth — foundations must be deep enough to reach stable ground, below the frost line, and away from tree root influence. Minimum 450mm for most soils, but clay soils or sites near trees can require 1.5m+ or piled foundations.
• Width — must be appropriate for the wall loading and soil bearing capacity
• Ground conditions — the inspector checks the soil type matches what was assumed in the design
• Trench condition — clean, level, no standing water, no loose material

This is the most critical inspection. Foundations are buried and cannot be checked later. If they are wrong, everything above them is compromised.

Builder tip: Never pour concrete before building control has inspected the trenches. If you do, the inspector may require you to expose them again.

When: After the DPC is laid, before the ground floor is constructed.

What they check:

• Damp-proof membrane is correctly installed, lapped, and sealed
• DPC height — at least 150mm above finished ground level
• Ground preparation — hardcore is compacted, blinding is in place
• Insulation — floor insulation positioned correctly

When: After drains are laid, before they are covered.

What they check:

• Falls — drains must have the correct gradient (typically 1:40 for 100mm pipes)
• Connections — properly connected to existing drainage or new soakaway
• Pipe type and size — correct for the application
• Bedding — pipes properly bedded and surrounded with pea gravel
• Air and water testing — the inspector may test the drains for leaks

When: After steel beams are installed, before they are boxed in or plastered.

What they check:

• Beam specification — correct size and grade as per the structural engineer’s calculations
• Bearing — steel is properly supported at each end with adequate bearing (typically minimum 150mm on padstones or concrete)
• Connections — bolted or welded as specified
• Fire protection — if required (common in loft conversions for party wall steelwork)

When: After all structural work, insulation, wiring, and plumbing are in place, but before plastering.

This is the most comprehensive inspection because it is the last chance to see everything before it is covered:

• Insulation — correct thickness and installation quality in walls, roof, and floor (Part L). No gaps, no compression, vapour barrier correctly positioned.
• Electrical first fix — cables routed correctly, consumer unit positioned appropriately
• Plumbing first fix — waste pipes, water supply, soil stack connections
• Ventilation — trickle vents in windows, extract fan ducting, air bricks
• Fire stopping — gaps around pipes and cables sealed with fire-rated material where they pass through fire-rated walls or floors
• Fire detection — smoke alarm positions and wiring
• Structural elements — lintels, wall ties, restraint straps
• Staircase (loft conversions) — rise, going, headroom, handrails, guarding

When: When all work is complete, including decoration, flooring, and external works.

What they check:

• Overall compliance — everything matches what was approved
• Safety glazing — critical locations have safety glass
• Electrical completion certificate — from a Part P registered electrician
• Gas safety certificate — if gas work was carried out
• Ventilation — extract fans working, trickle vents open
• Smoke alarms — mains-wired, interlinked, and tested
• Fire doors — FD30 doors on the staircase route (loft conversions)
• External finishes — render, brickwork, roofing complete
• Drainage — surface water and foul water systems complete and functioning

If everything passes, building control issues a completion certificate. This is the essential document that confirms the work meets building regulations. Keep it safe — you will need it when you sell.

Minor issues — the inspector may flag them verbally or in writing and ask your builder to correct them before the next inspection. Common examples: a small gap in insulation, a missing fire stop, a handrail that is too low.

Significant issues — the inspector will issue a formal notice requiring correction. For example: foundations not deep enough, insulation not meeting Part L standards, or structural steelwork not matching the engineer’s specification.

Safety issues — the inspector can require work to stop immediately if there is a risk to safety. This is rare but can happen with electrical faults or structural instability.

In all cases, the goal is to get the work right. Fixing problems during construction is far cheaper than fixing them after plastering and decorating is done.

• Give notice. Call building control at least 24 hours before each inspection stage. Do not cover up work before they have seen it.
• Keep the site accessible. The inspector needs to see foundations, steelwork, insulation, and drainage.
• Have paperwork on site. Structural calculations, the approved plans, and any manufacturer certificates for materials.
• Ask questions. Inspectors are usually happy to explain requirements and advise on how to achieve compliance.
• Do not take it personally. If an inspector requests changes, it is not a criticism — it is the system working as intended to keep your building safe.