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Description
Insulating material injected into the cavity of a cavity wall. The U-value achieved depends on the cavity width (average 65mm in the UK) and the insulating material. A number of insulation materials can be used with the most common being mineral or glass fibre, but polystyrene beads, Urea-formaldehyde foam and polyurethane foam and are also available
Unit cost of installation
The cost of a typical installation for most insulation materials is up to £500, although prices vary markedly. Poly-urethane foam is much more expensive (£2500), although has advantages in specific situations (see Technical Suitability below)
Bulk cost of installation
Data not available.
Indicative cost and carbon saving
Maintenance
None.
Lifetime
Life of dwelling.
Technical suitability
Systems are available that can be used in any wall up to 12 metres in height, provided the installation is undertaken by approved installers to the appropriate BBA or British Standards Institute standard. In other circumstances installations may be allowed up to 25 meters in height provided certain conditions (such as absence of raked joints in brickwork) are met - further detail can be found in CE16/GPG 26 'Cavity insulation in existing housing'.
Problems with rain penetration are rare especially if walls are rendered, and warranties are available for most systems (except Polyurethane systems) from the Cavity Insulation Guarantee Agency (CIGA). Polyurethane foams can be used in situations where the wall ties have begun to corrode to bond the two leaves of the cavity together. This negates the need for replacement of wall ties and potentially rebuilding, and so can be a cost effective solution. However, if the mortar bed joints have already split, replacing the wall ties may be required regardless.
Non-technical constraints
No specific issues.
Potential concerns with fuel poor
No specific issues.
Ancillary benefits
Work is undertaken from outside, so there is no disruption to tenants.
Trigger points for work
When general refurbishment of the external wall is being undertaken, or when structural work is being considered. (N.B. Building Regulations Approval is required in England & Wales whenever any thermal element is renovated)
Performance Limitations
Mineral fibre and Expanded Polystyrene bead CWI have BBA certificates for use in all areas: Urea Formaldehyde Foam has a BSI certificate with certain restrictions in severe weather zones, including coastal areas. The Cavity Insulation Guarantee Agency (CIGA) can supply guarantees that apply to all domestic retro-fit installations - it is not applicable to new build. High rise blocks require notification to local authorities, as a means of supervision. Some polyurethane systems are covered by BBA certificates.
Technical Guidance Available
» CE16/GPG 26 'Cavity insulation in existing housing'
» CE57 Refurbishing cavity-walled dwellings (2004 edition)
» GIL23 Cavity wall insulation: unlocking potential in existing dwellings (2002 edition)
» Cavity Insulation Guarantee Agency (CIGA) 01525 853 300 www.ciga.co.uk
» National Insulation Association Ltd (NIA) 01428 654011 www.insulationassociation.org.uk
» The Cavity Foam Bureau 0121 544 4949
» BUFCA (British Urethane Foam Contractors Association) 01428 654011 www.bufca.co.uk
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