Domestic basement construction projects

What you need to know as a busy builder

Constructing a basement conversion underneath a domestic property is specialised high-risk work that can catastrophically affect the stability of existing buildings. The project architect and engineer must provide detailed plans of the finished basement. The builder must use these plans, together with knowledge of the ground conditions on site, to make sure the construction work is planned and undertaken safely as well as ensuring all basement waterproofing considerations have been taken into account. This includes identifying any temporary works such as trench supports or propping arrangements that are required to ensure the stability of any excavation or existing buildings. Temporary works are the responsibility of the builder and should be planned by a competent person, normally known as the temporary works engineer.

Before work starts

Appoint a competent temporary works engineer to design the propping, shuttering and other support needed to prevent collapse of any excavation or building.

Devise a construction sequence that includes when and how you will install any temporary works required.

Identify how you will provide and maintain safe access for plant and personnel, removal of excavated material and ground water and ensure basement waterproofing has been taken into account.

Decide if the work area is a confined space – provide forced ventilation if necessary. Identify where underground services are and how you will protect them.

When work starts

Install the required temporary works and maintain them according to the temporary works engineer’s instructions.

Support all sides of every excavation to prevent ground or building movement and collapse.

For information about health and safety, or to report inconsistencies or inaccuracies in this guidance, visit