Basement 4, specialist in high quality, bespoke basement conversions and cellar conversions.

Using only the best quality materials and products available with our specialist teams of installers.

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Basement Creation (Underpinning)

QuickTime Movie

This movie shows basement creation

( Movie created by Tigershark Productions )

Where a basement does not exist or is unusable in it's present form, one can be created by lowering the base level of the foundation by means of underpinning.

Basement 4 can organise all statutory documents including Building Warrant and Party Wall notices, this is legislation that covers excavation work done on, or near a shared wall or boundary, more information is available from All structural design work is carried out by our chartered structural engineer and is fully insured.


Small section of wall with a reinforced structural joist or RSJ Remove soil and debris from the basement

The first stage of construction involves the removal of a small section of wall with a reinforced structural joist or RSJ fitted to carry the load, this hole will then be used to remove soil and debris from the basement avoiding any removal through the existing house.

Excavation and Underpinning

Basement underpinning stage 1 Drainage sump and land drains

To maintain structural integrity to the building and allow works to be carried out, a tried and tested method is used which involves the ground being excavated in alternate sections throughout the whole basement and reinforced concrete shuttered and poured under the exposed and existing foundations. Once this is set the same process is then applied to the adjacent sections ensuring uniform structural support at all times, when this is completed the floor level can be lowered to base of the new foundation and a basement is created.

Windows and Drainage

Fit basement windows Basement sump and drainage

From the structural design, new windows can be formed and concrete poured again with RSJ's placed to support the brickwork above. A hole is dug in one corner and a sump placed into this, land drains are then fitted around the full perimeter of the basement to transport any collected water to the sump, which is then removed by two electric pumps connected to the mains drainage.

Waterproof Membrane and Solid Structural Floor

Hardcore in-fill and waterproof membrane Concrete poured to give a solid structural floor

The drains are covered with hardcore in-fill and a tough and durable waterproof membrane is around the whole basement. Once this is done a steel mesh is placed and concrete poured to give a solid structural floor of between 100mm and 150mm deep, depending on the structural engineers design. This reinforced concrete slab will prevent any lateral movement to the new foundations.

75mm extruded insulation panels fitted Heavy duty DPC membrane is fitted

75mm extruded insulation panels are then fitted over the entire floor area and a heavy duty DPC membrane is fitted on top, underfloor heating sits above this giving a controlled uniform heat to the whole floor. A self levelling floor screed is poured and once dries, gives a smooth level surface ready for the final floor finish.

Stairway, First fix electric's and plumbing

Basement stairway fitted Basement stud wall and insulation board fitted

A break through is created in the existing ground floor joists and made structurally sound ready to support the new stairway. First fix electric's and plumbing are then installed and sound insulation placed between the floor joists, heat resistant fire-board is fitted to the underside of these joists and a metal stud framework is built around the perimeter of the basement. Extruded insulation panels are placed between these uprights and plasterboard is then fitted throughout, this is given a two coat wet plaster finish that provides a smooth surface for painting.

Second fix electric's and final work

Second fix electric's Finished basement

Second fix electric's including down-lighters and smoke hoods and a mains wired smoke alarm are then installed along with all remaining carpentry work, as an optional extra, Basement 4 can organise painting and decorating or alternatively leave the final touches to yourself.

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