If you’re embarking on a home extension but not familiar with all the terminology, you’ve come to the right place. We’ll walk through some of the key construction jobs that will be taking place in your property and explain their function.
Foundations
There are different types of foundation, each of which depend on several factors. These include the type of soil, groundwater levels, presence of radon gas, and any potential soil contamination.
Strip or trench foundations are the most common for a single storey extension. These are about a metre deep, filled with hardcore, concrete and steel reinforcement and extend around the perimeter of the extension. Pad foundations are rectangular or round areas of concrete used to support a single column in a building. Raft foundations are slabs of reinforced concrete and cover the entire footprint of the proposed extension. In some cases, such as in poor soil conditions, deeper foundations such as mini piles and concrete ground beams may be used.
The function of the foundations is to evenly distribute the load of the new extension across its footprint. To do this safely, foundations must meet Building Regulation requirements so choosing the most appropriate type of foundation is vital.
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Framework
The framework of your extension refers to the walls, floors and roof and can be constructed from a variety of materials such as bricks and blocks, timber or structural insulated panels (SIPs). Blocks and bricks are the most common and popular choice due to their lower cost and ready availability. However, timber frame and SIPs are popular for their sustainability and energy efficiency, respectively. Prefabricated frameworks are also gaining in popularity as they significantly reduce the build time and associated disruption.
When complete, the framework of an extension is ready for the next phase of the project which is the first fix of carpentry, electrics and plumbing. This can only be done when the structure is water-tight and protected from the weather.
First fix
First fix carpentry is the construction of internal stud walls, door and window frames, floor joists, roof trusses and stairs, if required. It adds structural stability to the extension and allows other trades such as the electrician and plumber to install their services around these structures.
The installation of electrical cabling, back boxes for switches and sockets, circuits and any wiring that needs to be hidden, is all part of the electrical first fix.
Plumbing first fix involves fitting pipework for water supply and wastewater drains to all parts of the extension. It also means conducting tests and pressure checks before the walls and ceilings are closed up.
If you’re worried about what to do with leftover construction materials, then it’s best to hire a professional.
Plasterboarding
With first fixes complete, the walls and ceilings in the extension can be covered up by plasterboard. Plasterboarding is sometimes known as dry lining as it is an alternative to wet plaster. The plasterboard forms the face of the internal walls as well as the ceilings and provides a smooth surface for decorative finishes such as paint or wallpaper.
Holes can easily be cut into plasterboard to allow cables and pipes to be passed through or for switches and sockets to be fitted flush to the walls. Variations of plasterboard are also used for their thermal and acoustic insulation or as part of fire protection for the extension.
Second fix
Second fix for carpentry, electrics and plumbing happens after the plastering of the walls and ceilings. In carpentry, this involves hanging doors, attaching skirting boards and architraves or other mouldings. For electrics, it means fitting the switches, sockets and light fittings to the walls and ceilings. It also involves connecting up the fuse board or consumer unit.
In plumbing, second fix is when the toilet, sink, bath, shower and other visible parts of your plumbing infrastructure are installed. It’s also when your boiler, radiators and any kitchen appliances are fitted. All plumbing installations are tested before the second fix is completed and a Part P certificate is required for any new electrical components as part of Building Regulations.