How external wall insulation works
This involves adding a weather-proof insulating material to the outside of your walls. The thickness of the insulation needs to be between 50 and 100mm in thickness and is usually installed where there are severe heat loss and damp problems or the exterior of the building requires repair work providing the ideal opportunity to add the insulation.
External wall insulation is more expensive than cavity wall insulation but it could save you about £380 a year on your fuel bills and it could pay for itself in 15 years.
A three bedroom semi-detached house could save nearly 2.5 tonnes of CO2 a year.
How it is installed
The cost of external wall insulation is around £2,500 for a semi-detached house*. The External Wall Insulation Association (EWIA) maintains a register of trusted systems and installers. If a professional system is used the work must be carried out by a specialist contractor but, local architect designed and approved systems can be installed by a good local builder.
*The marginal cost includes the insulation and labour when other wall repairs are being done at the same time. The full cost of installation (ignoring any remediation costs is typically around £6,000 for a semi-detached house, with a payback of around 15 years).