Cavity walls were first built in the UK in late 1920s. Before then, all external walls were solidly built in brickwork or stonework or a combination of both. The width of the cavity, which is bridged by wall ties between the inner and outer leaves, is 50mm (2 inches). The outer leaf of the wall is usually 112mm facing brick and the inner leaf is 100mm blockwork.
The cavity itself can provide both sound and heat insulation but in recent years the efficiency of cavity wall insulation has been increased by the use of other materials. A side benefit of this is that the inside of the house will require less heating so reducing the amount of carbon emissions by using less electricity or gas.
Different materials are used to insulate the cavity depending upon whether the house is existing or a new one under construction. Building regulations were changed in 1982 and now all cavity walls built since then have been insulated. Only houses built between say 1930 and 1982 may have cavities that are not insulated now.
The insulation can be installed quite easily by drilling holes through the outer leaf of the wall and pumping mineral glass/wool fibre or similar into the cavity. The holes are drilled at regular intervals in the wall and are patched up in matching mortar afterwards. The size of the house determines how long the process takes but a standard three-bedroom detached house should take about three to four hours.
Finding out whether an existing wall is a solid or a cavity wall can be determined quickly. In a cavity wall, the external face will consist entirely of bricks where the long face of the bricks are on view – except where an ornamental feature has been created. If the ‘end of a brick’ appears in the bonding pattern, the wall is a solid one. In new houses glass wool or rock wool panels are inserted as the external wall is being built.
It is claimed that about 30% saving in heat costs can be achieved by insulating the cavities in walls producing savings of over £100 a year for the average sized house. A 25 year guarantee is usually available from the installer. It is important that the installer carries out a survey of the property before work is commenced to ensure that there are no hidden problems.
There are government grants available for this type of insulation work. A grant of approximately 50% of the cost of the installation can be claimed by all householders and private tenants irrespective of income. A 100% grant is possible for people over 70 years old and also to a wide range of benefit receivers.