Building Control for a House Extension: What Gets Checked?
Understanding building control for a house extension in Wakefield can make the whole building process feel much less complicated.
Building Control inspections take place at important stages of an extension to check that the work complies with Building Regulations. This can include inspecting the foundations, drainage, damp-proofing, insulation, structural steelwork, roof construction and the completed extension.
The inspector does not normally watch the work every day. Instead, they visit at certain stages when important parts of the construction are still visible.
At CG Building Services, we help organise these inspections during the build and make sure the inspector is contacted before work is covered up.
What is the purpose of Building Control?
Building Control helps make sure that an extension is structurally sound, properly insulated, safe in the event of a fire and provided with suitable drainage and ventilation.
Building Regulations and planning permission are two separate things.
Planning permission mainly considers whether an extension can be built in a particular location, along with its size, position and appearance. Building Control looks at how the extension is actually constructed.
An extension may be allowed under permitted development without a full planning application, but it will usually still need Building Regulations approval.
For more information about the wider regulations, you can also read our guide to Building Regulations for House Extensions in Wakefield.
Before construction begins
Before work starts, a Building Regulations application will normally need to be submitted through either a Full Plans application or, where suitable, a Building Notice.
A Full Plans application usually includes detailed construction drawings, specifications and any necessary structural calculations. These documents can be checked before the work begins.
A Building Notice can be a quicker process for certain smaller projects, although detailed plans are not checked and approved in advance in the same way.
For a substantial house extension, having proper drawings and structural calculations before starting can help avoid uncertainty once construction is underway.
When does Building Control inspect a house extension?
The exact inspections required will depend on the design of the extension, the ground conditions and the type of work being completed.
However, the following are some of the most common stages inspected during a house extension.
1. Commencement of the work
Building Control must be informed when the building work starts.
The first visit may allow the inspector to look at the site, discuss the proposed work and confirm which future stages they need to inspect.
It is important that the builder and inspector communicate throughout the project. The inspector may not need to attend every stage listed in this guide, as the inspection schedule can vary from one extension to another.
2. Foundation trenches
The foundation inspection is one of the most important stages of building control for a house extension in Wakefield.
The inspector will normally want to see the foundation trenches before any concrete is poured. They may consider:
- The depth and width of the trenches
- The condition and load-bearing ability of the ground
- Nearby trees and tree roots
- Existing drains and inspection chambers
- Changes in ground level
- Signs of filled, disturbed or unsuitable ground
A standard foundation design may be suitable for many extensions, but this cannot always be confirmed until the ground has been opened.
If poor ground, deep drainage, large trees or previous building work are discovered, the foundations may need to be altered or dug deeper.
Concrete should not be poured until the necessary foundation inspection has taken place or approval has been given to proceed.
3. Drainage
Any new or altered drains will normally need to be inspected before they are covered.
Building Control may check:
- The route of the drainage
- The fall of the pipes
- The type and size of pipe being used
- The material supporting and surrounding the pipes
- The position of bends and junctions
- Access for future cleaning or maintenance
- Connections to foul-water and surface-water systems
Drainage sometimes causes unexpected work during an extension, particularly when old pipes do not follow the route shown on existing plans.
If a drain runs beneath the proposed extension, it may need to be protected or diverted. Separate permission may also be needed if the work affects a public sewer.
The drains may need to be tested before the project is completed.
4. Ground floor preparation
Before a solid floor is concreted or covered, the inspector may want to check the different layers beneath it.
Depending on the design, these can include:
- Compacted hardcore
- Sand blinding
- Damp-proof membrane
- Gas or radon protection where required
- Floor insulation
- Concrete floor construction
- Perimeter insulation to reduce cold bridging
The damp-proof membrane needs to be installed carefully and connected correctly to the damp-proof course in the walls.
Once concrete or flooring has been installed, these materials can no longer be seen. This is why inspections must be arranged at the correct time.
For suspended timber floors, Building Control may instead check the floor structure, insulation and ventilation beneath the floor.
5. Damp-proof course, walls and insulation
As the walls are constructed, Building Control may inspect the damp-proof course, cavity construction and insulation.
They may check:
- The height and position of the damp-proof course
- Cavity widths
- Wall ties
- Cavity insulation
- Insulated cavity closers around openings
- Lintels above windows and doors
- The connection between the new and existing walls
- Fire stopping and cavity barriers where required
Wall insulation must be installed properly without large gaps. Poorly fitted insulation can create cold areas that increase the risk of condensation and heat loss.
The inspector may need to see the insulation before the cavity or internal wall is completely closed.
6. Structural steelwork and knock-throughs
Many modern extensions involve removing part of the original external wall to create an open-plan kitchen or living area.
A structural engineer will normally calculate the steel beams and supports needed to carry the weight above the opening.
Building Control may check that:
- The correct steel beam has been installed
- The steel matches the structural calculations
- The bearings are long enough
- Suitable padstones or supports have been provided
- Bolted steel connections match the engineer’s details
- Columns and supporting walls are suitable
- The steel has the required fire protection
Any changes to the steel design should be discussed with the structural engineer and Building Control before being carried out.
Changing the steel size, removing a column or altering the opening without updated calculations can cause delays and may prevent the work from being approved.
7. Roof construction
The roof may be inspected before plasterboard and internal finishes cover the structure.
For a pitched or lean-to roof, Building Control may consider:
- The size, grade and spacing of the roof timbers
- The roof pitch
- Support around roof windows
- Structural beams
- Restraint straps
- Roof ventilation where required
- The position and thickness of insulation
- Weatherproofing details
For a flat roof, they may check the direction of the fall, joist sizes, insulation, ventilation and roof build-up.
The roof covering must also be suitable for the pitch. This is particularly important with roof tiles and roof windows, which have minimum installation pitches.
8. Fire safety and ventilation
Building Regulations include requirements intended to protect people if a fire occurs.
Depending on the design of the property, Building Control may check smoke alarms, escape arrangements, fire-resistant construction and protection around structural steelwork.
Ventilation is also important.
Kitchens, utility rooms, bathrooms and toilets may require mechanical extractor fans. Background ventilation through windows or other approved systems may also be needed.
Good ventilation helps remove moisture and reduces the risk of condensation and mould.
9. Windows, doors, heating and electrics
The inspector may also check that new windows and doors meet the required standards for insulation, safety glazing and ventilation.
Electrical work should be completed by a suitably qualified electrician. The relevant electrical certificate will normally be required when the extension is completed.
Heating work, boilers and other services may also need certificates from competent installers where applicable.
These certificates should be kept safely, as they may be needed before Building Control can issue the final completion certificate.
10. The final Building Control inspection
Once the extension is substantially complete, a final inspection should be arranged.
The inspector may look at:
- The completed structure
- Drainage and rainwater disposal
- Windows and safety glazing
- Ventilation
- Smoke alarms
- Insulation and energy-efficiency information
- Electrical and heating certificates
- Any outstanding items from previous inspections
- Whether the work matches the approved drawings and calculations
Any remaining issues may need to be corrected before the extension can be signed off.
Once Building Control is satisfied and the necessary completion information has been provided, a completion certificate can be issued.
This certificate should be kept with the paperwork for the property. A solicitor, buyer or mortgage lender may ask for it if the house is sold or remortgaged.
Who arranges the Building Control inspections?
The homeowner is ultimately responsible for making sure that the necessary Building Regulations process is followed. However, an experienced extension builder will normally help manage the inspections during construction.
At CG Building Services, we arrange inspections at the relevant stages and communicate with Building Control while the extension is being built.
This means homeowners do not have to work out when foundations, drains, insulation or structural work need to be inspected.
However, it is always sensible for the homeowner to keep copies of the application, approved drawings, structural calculations, certificates and final completion paperwork.
Common problems that can delay Building Control sign-off
Several avoidable issues can delay the final certificate:
- Work being covered before it has been inspected
- Structural steelwork not matching the engineer’s calculations
- Missing electrical or heating certificates
- Changes being made without updating the drawings
- Insulation being installed incorrectly
- The final inspection never being requested
- Outstanding items from earlier inspections not being completed
The easiest way to avoid these problems is to plan the project properly and maintain communication between the builder, architect, structural engineer and Building Control inspector.
Does Building Control guarantee all the building work?
Building Control inspections are an important part of the process, but they do not replace the need to appoint a competent and experienced builder.
The inspections check compliance with Building Regulations at selected stages. They are not the same as continuous site supervision and do not manage the homeowner’s contract with the builder.
A good builder should follow the drawings, use suitable materials and complete the work properly whether or not an inspector is standing on site.
Building control for a house extension in Wakefield
Properly managing building control for a house extension in Wakefield helps the project progress smoothly from the first excavation through to final sign-off.
The main thing is to arrange inspections before important work is covered. Foundations should be inspected before concrete is poured, drains before they are backfilled, and insulation or structural components before they disappear behind floors, walls and ceilings.
At CG Building Services, we build house extensions throughout Wakefield, Leeds and the surrounding areas. We work with architects, structural engineers and Building Control to help ensure every stage is completed properly.
If you are planning a house extension and would like an experienced local builder to manage the complete construction process, contact CG Building Services to discuss your project.
