Substructure and ground-bearing floors

Also see:

5.1.21Thermal insulation

Ground-bearing floors and walls below the DPC shall be thermally insulated to comply with building regulations and be suitable for the intended use. Issues to be taken into account include:

  1. floor insulation
  2. wall insulation
  3. cold bridging.

Floor insulation

Thermal insulation materials for use below ground-bearing slabs should have:

  • appropriate density for the location
  • low water absorption.

Insulation to be positioned below both the slab and DPM should be resistant to ground contaminants. The following materials are acceptable for use as insulation:

  • expanded polystyrene boards (grade EPS 70) to BS EN 13163
  • a proprietary material that complies with Technical Requirement R3.

Wall insulation

Cavity insulation materials, super lightweight blocks, blocks with face bonded insulation or integral insulation should be:

  • manufactured and used to comply with a British Standard and relevant code of practice, or
  • used in compliance with Technical Requirement R3.

The thickness of materials should be suitable for the required level of performance:

England and WalesSee Clause 6.1.7.
Scotland■ Not permitted to fill the full width of the cavity with any thermal insulants at the time of construction.
Northern Ireland and the Isle of Man■ Not permitted to fill cavities with pumped thermal insulants at the time of construction.

Cold bridging

The design should ensure that any risk of cold bridging is minimised, especially at junctions between floors and external walls. Precautions include:

  • extending cavity insulation below floor slab level
  • linking floor and wall insulation
  • providing perimeter insulation to floors
  • facing supporting substructure with insulation – where homes are stepped or staggered, the wall forming the step or stagger may require insulation.