Concrete floor

Project Overview

This retrofit basement project included turning an existing basement into a much large and more usable space. This was done by increasing the floor to ceiling heights in the existing basement. The second part to the project was to create a space under the house where there was no basement before.

This is known as a “retrofit basement”.

Project Details

Location: Central Birmingham
Surface Area: 46 square metres
Completed: 2020
Architect: N/A Drawings by Beautiful Basements

Stage 1 - Excavating & underpinning

Excavating under the house

Firstly the team had to open the areas that had previously not been included within the basement (see original plans here). This is done by carefully supporting the existing house and excavating section by section.

Eventually the proposed basement (plans here) was fully excavated and the underpinning could begin.

Underpinning & lowering the floor

The second part was to excavate under all of the existing basement walls. When excavated they were supported temporarily, finally cast with concrete. In some areas this lowered the floor by around 1.2m in places.

Stage 2 - Structural works & waterproofing

Structural works

With the walls of the basement all lowered and supported the next step could begin. The remaining soil was removed, excavate & cast a sump in place, level the floor and compact it to give a firm base. Timber was fitted around the perimeter of the basement to form a drainage channel. This channel allows incoming water to be directed to the sump & pumping station.

A layer of plastic was then laid to prevent the new concrete dying out too fast. On top of this the steel reinforcing as drilled into the concrete underpinning. Steel reinforcing mesh was laid tying together the walls and floor.

Levelling rails were installed and finally the concrete was cast, completing the new structure.


The basement was waterproofed using a Type C, Drained Cavity System. Supplied by Triton Systems. The cavity drainage membranes on the walls and floor were linked via the perimeter drains to a sump and pumping station, which would discharge all water automatically.

Once complete the basement could be insulated, dry lined and finished to the specifications set out by the clients.

Take a look at some of our similar previous retrofit basement projects. Or click below to contact us and get a quote