Building Control Inspections: What Happens at Each Stage of Your Extension?
Building control typically inspects a house extension in England at 7 key stages: foundations, damp-proof course (DPC), roof structure, weather-tight stage, insulation, drainage, and the final inspection that leads to the completion certificate. Each stage should be inspected and passed before the work is covered up or the build moves on.
The inspector isn’t there to redesign your extension. They check what has actually been built against the Building Regulations and the approved information. The builder usually books the inspections, and if one is missed and the work gets covered up, homeowners can end up with some very serious problems.
At Kirkwood Architects, we deal with Building Regulations and structural engineering as part of our process, so building control inspections are something we know well. Here is what happens at each stage and what to watch for.
- What is a building control inspection?
- Who books the building control inspection?
- The 7 building control inspection stages
- What about building control inspections for loft conversions?
- How long does a building control inspection take?
- What happens if a building control inspection fails?
- What are the most common reasons building control raises issues?
- Why the Building Regulations drawings matter
- Should the homeowner attend building control inspections?
- What happens if the builder carries on without building control?
- Local authority or private building control?
- What happens when the project is finished?
- Why design, structural engineering and building control need to work together
- The key thing for homeowners to remember
- Frequently Asked Questions
What is a building control inspection?
It is an inspection carried out by the relevant building control body during construction. For a typical domestic project in England, you can use your local authority building control department or a private registered building control approver. The inspector visits at certain stages and checks that the work complies with the Building Regulations.
The exact stages depend on the project. A straightforward single-storey extension has different requirements from a loft conversion, and a complicated project may need additional inspections. What matters is that the builder knows when inspections are required and books building control in before covering up work that needs to be seen.
Who books the building control inspection?
Usually the builder does, but you should be aware of it too. Don’t assume that because building control has been appointed, the inspections are automatically happening. We have seen builders tell homeowners that building control is appointed when it isn’t, and that the inspector is “happy” when nobody has actually visited. If you have paid someone to build your extension, you need to know the correct inspections are taking place.
The 7 building control inspection stages
The exact stages depend on the project, but for a typical house extension these are the key points where building control inspects the work.
Stage 1 — Foundations
Before the concrete is poured, building control inspects the excavation. The inspector looks at the depth and width of the foundations, the ground conditions and whether what has been dug suits the foundation design. It matters because you can’t see what is going on once the concrete is in.
If the inspector isn’t happy, the builder may need to make changes before pouring. This is also where unforeseen ground conditions show up, such as old foundations, tree roots or poor ground. If something significant is found, the structural engineer may need to revisit the foundation design.
Stage 2 — Damp-Proof Course (DPC)
An inspection generally takes place before the damp-proof course and other relevant elements are covered up. The inspector needs to see the construction while it can still be properly checked, because once it is covered, it is much harder to inspect.
Stage 3 — Roof Structure
For an extension, the inspector checks the roof structure and how it has been built. For a loft conversion, there is considerably more going on: the structural alterations to the existing roof need checking, particularly where steels, new floor structures or dormers are involved. This is where the Building Regulations drawings and structural calculations become important, because the inspector checks the construction against them.
Stage 4 — Weather-Tight Stage
Once the building is substantially weather-tight, the inspector can assess the roof, external construction, windows and doors and other parts that need to comply. The exact requirements and timing depend on the project.
Stage 5 — Insulation
Insulation may need inspecting before it is covered. The inspector checks it has been installed correctly and the relevant construction details have been followed. Once walls, ceilings or floors are closed up, they can’t see what is behind them, which is why timing matters.
Stage 6 — Drainage
Where new drainage is installed or existing drainage altered, the inspector may need to see it before it is covered over. This is particularly relevant where an extension introduces new bathrooms, kitchens or other drainage runs.
Stage 7 — Final Completion Certificate
Once the work is finished, there is generally a final inspection. The building control body checks the completed work and the information available before issuing the completion documentation. For local authority building control, that is the completion certificate; for a registered private approver, it is the final certificate issued under the private regime. You don’t just want the extension finished physically. You want the building control process finished too.
What about building control inspections for loft conversions?
Loft conversions can have slightly different requirements because so much is happening within the existing structure. The inspector may need to check:
- New structural floor arrangements, steel beams and the connections between them
- New or altered stairs
- Fire protection and means of escape
- Insulation, roof and dormer construction, and windows
- Electrical and other relevant building services
The exact requirements depend on the design. It is one reason we prepare the Building Regulations drawings and structural calculations properly from the start: the more that has been considered before construction, the easier it is for the builder and inspector to see what should be there.
How long does a building control inspection take?
Not hours. In our experience an inspection is often relatively quick, and we have rarely seen an inspector spend more than around ten minutes on a straightforward one, although it depends on what they inspect and what they find. They look at the work, check the drawings and information, take photographs and record what they have seen. The inspection report documents the work inspected, any contraventions and the action taken to resolve them.
Book a Free Discovery Call
No, you don’t need a registered professional carrying that specific title for a house extension. What you do need is proper planning drawings, structural engineering, and building regulations drawings, and Kirkwood produces all three in-house for extensions across Chelmsford, Brentwood, Billericay, Wickford, Basildon, Rayleigh, Leigh-on-Sea, Southend, and the surrounding areas of Essex.
What happens if a building control inspection fails?
If something isn’t right, it needs to be corrected. The inspector may require the builder to put it right before the project continues. Sometimes that is straightforward; sometimes it is more complicated. Occasionally there is an issue nobody could reasonably have identified before the building was opened up: a removed floor reveals something unexpected, a wall exposes a structural condition that wasn’t visible, or the ground turns out different from what the foundation design assumed.
In those situations, we may need to revisit the structural design and produce revised calculations or details. That is part of construction. You can’t always see everything until you start opening the building up.
What are the most common reasons building control raises issues?
Unforeseen conditions
This is the hardest to avoid completely. You can survey the property, take measurements and prepare detailed drawings, but you don’t have X-ray vision. You don’t know what is behind every wall or under every floor until it is opened up. If that leads to a structural change, we deal with it.
Poor workmanship
If the builder isn’t following the drawings, calculations or Building Regulations, building control can pick it up during an inspection. That is why choosing an experienced builder matters so much. The best drawings in the world can’t help if they aren’t followed.
Different inspectors, different views
Different inspectors can take different views on particular details, which can be frustrating for homeowners, builders and designers alike. When we disagree with an interpretation, we go back to the drawings, calculations and requirements and work through it. The important thing is not to ignore the inspector because you disagree. Resolve the issue properly and document what has been agreed.
Why the Building Regulations drawings matter
We don’t stop at the drawings needed for planning permission and leave the builder to work the rest out. We produce the structural engineering and building regulations drawings so the construction team knows what is required. Structural elements, insulation, fire safety, drainage and construction build-ups have all been considered before the builder starts. If the builder then follows the drawings and does a good job, there shouldn’t be any reason for building control to find major problems.
Should the homeowner attend building control inspections?
Ideally, yes. We recommend you know when inspections are taking place and, where practical, are present. You are paying for the project, so you should know the foundations have actually been inspected, that building control has attended, whether they raised any concerns, and when the project has passed each stage.
We have unfortunately seen homeowners trust the builder completely and stay out of the process, only to discover later that building control hadn’t been appointed, or hadn’t inspected the work as they were told. That is when things can become very serious.
What happens if the builder carries on without building control?
If a builder pours foundations without the required inspection, or covers up work before building control has had the chance to inspect it, you potentially have a problem. The point of the inspection is to check the work while it is visible. Building control may need the work exposed again, and in the worst cases, defective work may need to be altered or removed. We have seen incorrect foundations cause major problems for a homeowner because the work was done without proper inspection. It is your house, and you are the one left with the consequences after the builder has moved on.
Don’t just take the builder’s word for it.
Don’t assume that because your builder says “building control is happy”, the work has actually been inspected and approved. Ask when the inspection is, who the building control company and inspector are, what they said, and whether the inspection report has been issued. A good builder shouldn’t mind you wanting to understand what is happening on your own project.
Local authority or private building control?
For most standard domestic projects in England, you can use either. Local authority building control is often cheaper, depending on the project and the council. Private approvers have different fee structures, and some builders have established working relationships with particular ones, which can make the process feel smoother.
Neither is automatically better. We have worked with both, and there are excellent inspectors in each. What matters is that the person inspecting understands what they are looking at and that the project is properly inspected and documented, not treated as a box-ticking exercise. Private companies carrying out this work in England now need to be registered as building control approvers with the Building Safety Regulator.
What happens when the project is finished?
Once construction is complete, the building control body carries out the final stage. If the work complies and the required information has been provided, the completion documentation is issued: generally a completion certificate for local authority projects, and a final certificate from the registered approver for private ones. Keep it with your other property documents rather than putting it in a drawer and forgetting it.
Why the completion certificate matters when selling your house
When you sell, a solicitor may want evidence that the building work was properly approved and signed off. GOV.UK notes that without the relevant approval, you may not have the certificates of compliance needed when selling your home. Missing documentation doesn’t necessarily stop a sale, but it can create complications you don’t need.
What if building control refuses to issue the completion certificate?
The issues need to be resolved. The process isn’t finished just because the builder has physically finished the extension. Any outstanding contraventions must be dealt with before the completion certificate or final certificate can be issued, which is another reason to deal with problems as they arise rather than at the very end.
Why design, structural engineering and building control need to work together
A house extension isn’t just four walls and a roof. You have the homeowner, the architect, the structural engineer, the builder, building control and sometimes a party wall surveyor. If they don’t communicate properly, problems arise. At Kirkwood, we deal with the design, Building Regulations and structural engineering together, so the structural calculations are produced alongside the technical drawings rather than leaving the builder to work out the structure afterwards. Everyone has one clear set of information, and building control can inspect the work against it.
The key thing for homeowners to remember
Building control inspections aren’t something to worry about. If your project has been properly designed, the structural engineering is done correctly, the drawings are accurate, and the builder is competent and follows them, the inspections should be fairly straightforward. Sometimes the inspector will raise something. If they do, it gets dealt with, and that is normal construction.
The problems start when inspections aren’t booked, work is covered up first, builders don’t follow the drawings or homeowners aren’t told what is happening. So keep everything transparent:
- Know who your building control company is
- Know when the inspections are taking place
- Know what the inspector has said, and keep the reports
- Make sure the project is properly signed off at the end
At Kirkwood Architects, we take the Building Regulations and structural engineering side of a project seriously from the beginning, so that building control is a straightforward part of the process rather than something that becomes a problem later. If you are planning an extension or loft conversion in Essex and want the technical side handled properly, book a free Discovery Call with the Kirkwood team.
Frequently Asked Questions
How many building control inspections are there for a house extension?
There is no single fixed number for every project. A typical extension involves around seven key stages: foundations, damp-proof course, roof structure, weather-tight stage, insulation, drainage and completion. The exact stages depend on the type and complexity of the work.
Who books the building control inspections?
The builder usually arranges them, but you should know when they are happening and make sure they actually take place.
Does the inspector need to see the foundations before concrete is poured?
Yes. The foundations need inspecting before they are covered or concrete is poured, so the inspector can assess the excavation and construction.
What happens if the builder pours the foundations before building control inspects them?
Building control may require the work to be exposed or investigated so it can be assessed. Depending on what is found, further work or structural advice may be needed.
How long does a building control inspection take?
A straightforward inspection is often quick. In our experience, many take around ten minutes, though it varies with the stage and anything the inspector needs to investigate.
Can building control fail an inspection?
Yes. If the inspector finds work that doesn’t comply, it has to be corrected or otherwise resolved before the project moves on.
What happens if building control finds an unexpected structural problem?
The structural engineer may need to reassess and provide revised calculations or details. It can happen when existing structures or ground conditions aren’t fully visible before construction starts.
Is local authority building control cheaper than private?
It can often be cheaper, but cost depends on the project and the authority. Private approvers set their own fees, and both routes can be used for qualifying projects in England.
Do I need a completion certificate for an extension?
The completion documentation is important evidence that the work went through the Building Regulations process, and solicitors may ask for it when you sell.
What if I can’t find my completion certificate?
Contact the relevant building control body to find out what records exist. If the work was carried out without the required approval, retrospective regularisation through the local authority may be an option in applicable circumstances.
Does Kirkwood deal with Building Regulations and structural engineering?
Yes. Kirkwood provides the Building Regulations drawings and structural engineering information needed to take a project from planning through to construction, so the technical design is settled before the builder starts.
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