Waterproofing of basements and other below ground structures

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5.4.5Structural stability

Elements forming a waterproofing structure below ground including: foundations, walls and floors, shall adequately resist movement and be suitable for their intended purpose. Issues to be taken into account include:

  1. site conditions
  2. structural design
  3. durability
  4. movement
  5. design co-ordination.

Site conditions

Parts of the building constructed below ground level that form the structural elements of usable spaces should be designed by an engineer in accordance with Technical Requirement R5 where they are retaining more than 600mm. Issues that should be taken into account include:

  • characteristics of the site
  • ground conditions
  • hazards.

Structural design

The structure should be designed to take account of all imposed loads and actions, including:

  • ground movement
  • lateral forces from ground water, retained ground and ground surcharge loads
  • buoyancy
  • loading from other parts of the building
  • temporary loading conditions.


The structure should be designed to be sufficiently durable against site hazards, including:

  • chemicals
  • frost action
  • cyclical wet-dry conditions.


Movement within the structure should be limited to the capacity of the waterproofing system’s resistance to such movement, ensuring that the designed level of watertightness is achieved. Detailed guidance for the limitation of movement should be provided where appropriate.

Movement joints in below ground waterproofed structures should be avoided. Where it is necessary to provide movement joints, the design should ensure satisfactory in-service performance, including watertightness. Such joints should be accessible for maintenance, and not permanently concealed by other structural elements of the building.

Design co-ordination

Structural design should be co-ordinated with the design of the waterproofing.