Building Process

Preparing the Site – The first stage of any extension is to clear the area where the extension will be built. This may involve demolishing existing structures, removing patios, plants and trees. Your property will also need to be protected as required.

Excavating Foundations – Once the site has been cleared, the new foundations will need to be excavated. Most builders prefer to use mini-excavators for this task (assuming that there is access to the site). Be prepared for large volumes of excavated material which will need to disposed off with grab lorries or skips. If you have poor ground conditions, your foundations may have to be specially designed and include piling or a reinforced concrete raft.

Concreting Foundations – Once the foundations have been excavated and approved by the council’s Building Inspector, they can be concreted. Most builders prefer to use ready mixed concrete for this if access is possible.

Drainage – Once the foundations have been concreted, any alterations to the storm (rainwater) and foul drains can be completed. This may involve moving existing manholes or creating new ones. Many extensions use ‘soakaways’ for rainwater disposal and these will need to be located at least 5m from any building.

External walls to dpc – The external walls can now be built to damp-proof course level (usually floor level) and the dpc installed.

Oversite – Depending on the type of floor you are forming, the concrete base is poured or the beams and blocks are installed.

External walls – The external walls can now be built and the extension is really starting to take shape. For single storey extensions, the walls will be built to ‘wall plate’ (i.e. roof) level and for two storey extensions, the walls will be built to first floor joist level. New window and door openings are formed.

Floor Joists – For two storey extensions, the first floor joists are fitted. There may also be steel beams to be fitted at this stage.

First Floor walls – For two storey extensions, the first floor walls can now be formed. This will normally involve the erection of a scaffold around the extension.

Roof Carcassing – The roof timbers can now be added which will either be pre-formed trusses or the roof will be ‘cut’ on site using individual roof timbers.

Fascias and Soffits – The fascias and soffits are now added.

Rooflights – Where required, rooflights are now added to the roof structure.

Roof tiling – The roof can now be felted, battened and tiled. Lead flashings, valleys and box gutters are also formed at this stage.

Windows and External Doors – new windows and doors are fitted which will ensure that the new extension building is secure and internal opening can be formed.

External finishes – if your extension is finished externally in rendering or other finishes such as tile hanging, this can now be completed.

Guttering and downpipes can be fitted (where the walls are rendered, the downpipes will be fitted after the rendering).

Internal Openings – Any new opening between the existing property and the extension can now be formed. This will often require the installation of new steel beams and lintels. Existing fixtures and fittings (eg kitchen units) are usually removed at this stage as required.

Internal Walls – Internal blockwork or studwork walls are now formed.

First Fix Services – The electrician and plumber can now complete their ‘first fix’ services including installation of pipework, cables, etc. The carpenter will fit any new internal door linings, ceiling hatches, etc. First fix refers to works that are completed prior to plastering.

Insulation and Plasterboarding – New sound and thermal insulation can now be added to the floors and roof areas prior to plasterboarding. Many builders use plasterboard as an internal finish to the new external walls.

Plastering – The ceilings and walls can now be plastered. Some builders prefer to dry line the plasterboard which avoids the need for complete plastering.

Floor screeding – The ground floor is now screeded with a sand:cement mixture, provided a smooth and level surface.

Suspended Floor Finishes – First floors are now fitted with flooring grade chipboard (this is sometimes completed prior to plastering). In some instances, solid floors can be finished with chipboard which acts as a floating floor. You may also have a timber engineered floor which would be fitted instead of the chipboard.

2nd fix electrics– With plastering complete, the electrician will now fit the switch plates, sockets and light fittings.

2nd fix plumbing and heating – The plumber will now fit any new sanitaryware and the new radiators. If you are having a new tanks, boiler or cylinder, it is usually fitted at this stage.

2nd fix carpentry– The carpenter will now fit internal doors, architraves and skirtings. New cupboards, wardrobes, kitchen and bedroom units can also be fitted at this stage.

Other finishes– Bathroom tiling, decorating, laminate or other floor finishes can now be completed.

Finishing touches– The final touches to your new extension can now be added such as furniture, curtains and blinds and pictures.

Completion – With the works complete, you can now enjoy the use of the additional space for many years to come.