5.1 Substructure and ground-bearing floors

Also see:

6.19.3

5.1.21 Thermal 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. thermal 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 for masonry cavity walls should be suitable for the required level of performance, see Clause 6.1.7.

Thermal bridging#

The design should ensure that any risk of thermal 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
  • particular attention should be paid to ensuring thermal bridging is addressed at door openings.

Last updated: 2nd January 2024

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