New & existing basement

Project Overview

A basement under a new extension as part of a major development of an old town house, Beautiful Basements was asked to provide waterproofing design, complete build, and waterproofing installation. The basement was partly under the existing house and partly under the new extension.

Project Details

Location: Birmingham
Surface Area: 72 square metres
Completed: 2022
Architect: Simplify Structural Engineering

Stage 1 – Site preparation, excavating under new extension

Opening the front of the house

To prepare the house for the basement under the new extension, the rear of the house supported and removed.


With the area prepared, the heavy machinery could gain access. The basement excavation took place in two phases. The first was the existing basement. It was lowered and all the house walls were supported and underpinned.

The second phase was to excavate and level the rear garden to allow the basement under the new extension.

New basement

The new slab was levelled, compacted, reinforced and then cast. The new basement under the extension had starter bars coming though to link the walls and slab.

The new walls were shuttered, had steel reinforcing added and supported to allow the walls to be cast in one section.

Ground floor

The structure for basement under the new extension was finished with a block and beam floor, creating the ground floor.

Stage 2 – Waterproofing

The new external walls under the new extension had to include a dual-protection system to satisfy the requirements of the warranty provider. Beautiful Basements was the designer and installer for both systems.

Primary System

Type B – Integral protection

All new external walls, the concrete slab were cast with concrete including a waterproof additive. The steel reinforcing within this structure was designed to reduce the cracking to less than 0.3mm, also providing integral protection. All construction and day joints have a crystalising waterproofing slurry and an expanding waterbar applied to them to waterproof natural weak points.

Secondary System

Type C – Drained cavity protection

At the base of all external walls a recessed concrete channel was created within the slab. All walls and the floor were lined with a cavity drainage membrane (CDM). These membranes were linked to sump chambers via the recessed perimeter channels. Within the sump is two pumps and a high-level alarm. This system is designed to catch any water that is not stopped by the primary system and discharge it automatically. Flushing and maintenance points were installed to allow future servicing of the system. The front and rear lower sections are linked with a underground pipe.

Both waterproofing systems were designed by Structural Surveyors in Structural Waterproofing (CSSW) in accordance with BS8102:2009

All waterproofing materials were supplied by Triton Systems Ltd

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