What This Requirement Covers
Cavity wall insulation (CWI) is one of the most cost-effective energy efficiency measures for existing homes. Most houses built between 1920 and 1990 have unfilled cavity walls that can be insulated to significantly reduce heat loss. The work must comply with the Building Regulations and should be carried out by a registered installer.
Key Requirements
Suitability Assessment
Before installing cavity wall insulation, a suitability assessment must be carried out
- The cavity must be at least 50 mm wide (and preferably 65 mm or more)
- The masonry must be in good condition with no significant cracking or missing mortar
- The wall must not be excessively exposed to driving rain (BRE exposure zone assessment)
- There must be no bridging of the cavity (partial fill insulation, wall ties with debris, etc.)
- Timber frame walls behind a masonry outer leaf are not suitable for injected CWI
Insulation Materials
- Mineral wool (blown fibre): Most common; suitable for most cavities; does not retain moisture if properly installed
- Expanded polystyrene (EPS) beads with adhesive: Good for exposed locations; water-resistant
- Polyurethane (PU) foam: Fills irregular cavities well but is not suitable for all situations
- Urea-formaldehyde (UF) foam: Largely superseded by other materials (see Approved Document D)
Standards and Guarantees
- Installation must comply with BS EN ISO 14683 and the relevant BBA certificate conditions
- Installers should be registered with the Cavity Insulation Guarantee Agency (CIGA), which provides a 25-year guarantee
- The installer must lodge a guarantee with CIGA, which transfers with the property on sale
- Building Regulations compliance is self-certified through the installer's competent person scheme registration
Practical Compliance Tips
- Obtain a pre-installation survey to confirm the cavity is suitable
- Check the BRE driving rain exposure zone for your property; highly exposed properties may not be suitable for CWI
- Ensure the installer is CIGA registered and that the guarantee is issued and registered
- If you experience damp problems after CWI installation, contact the installer and CIGA promptly
- Keep the CIGA guarantee certificate with the property documents
- CWI is not suitable for all properties; alternatives include external wall insulation or internal wall insulation
- Consider combining CWI with other energy improvements (loft insulation, boiler replacement) for maximum benefit