What is a Cavity Wall?
A cavity wall is made up of two masonry brick walls running parallel to one another with space (cavity) between them of at least 40mm. Masonry bricks are absorbent, so moisture absorbed by the outer wall typically drains through the cavity, rather than coming into the home, helping to prevent damp issues. This type of wall construction can be found on properties build around the late 1800’s to the 1900s superseding solid walls and as time has gone on, the size of the cavity between the two skins of brick has continued to grow – a typical cavity wall from 1900’s to 1980’s is between 280-300mm thick, giving a cavity width of between 40mm to 60mm. Properties built after the 1980’s can have cavity widths of up to 100mm and new build properties built from 2010 onwards may have cavity widths of up to 165mm.
Although some builders began insulating cavity walls in the 1980s, it only became compulsory under building regulations to do so from 1983 although, some buildings had been passed on building control prior 1983 yet not finished building until after 1983, these properties may not have cavity wall insulation. As such there are many properties in the UK that currently have unfilled cavity walls. The good news is that these can be insulated very easily!
A home can lose as much as 35% of the heat loss through uninsulated external walls. Therefore if these can be insulated, the home retains heat better, which means lower energy bills. The concept of insulating a cavity wall is really very simple – it involves filling the cavity between the two skins of masonry bricks with an insulating material, which slows the movement of heat through the wall.
How does cavity wall insulation work?
If a hot room is partitioned from the cold by a wall, heat will move through the wall, eventually cooling the room until an equilibrium is reached, where the outside temperature is equal to the inside temperature. In reality this very rarely happens, because rooms tend to be heated, so as some heat escapes through the wall, more hot air is supplied, keeping it at a comfortable ambient temperature. If the thermal gradient is larger, (e.g. on a cold and wintry day), the movement of thermal energy across the wall will be accelerated.
Insulating a cavity wall helps to provide a thermal barrier, which slows the flow of heat out of a room considerably. By slowing down the rate at which heat escapes from the home, less heating is needed to keep the house at the required temperature. In the summer, the reverse happens; hot air outside the home can’t get in as easily, which means you don’t need to use energy to keep the home cool. Therefore in both summer and winter, cavity wall insulation can make an enormous difference to your energy bills. The process is relatively quick and inexpensive, so it is certainly worth considering.
Savings from cavity wall insulation
Although the savings from cavity wall insulation vary greatly from property to property, for an average size three bedroom home, the energy savings from installing cavity wall insulation should amount to £150 per year. With an installation cost of £500-600, the savings you create from installing the cavity wall insulation should pay for the work in under 4 years.
- Insulating your cavity walls will help you to heat your home more efficiently, saving about £275 for a typical 4 bed detached house.
- Cavity wall insulation will payback in 3 to 4 years for the investment giving lower heating bills .
- According to the Energy Saving Trust, cavity wall installation can reduce carbon dioxide emissions (CO2) by 560kg.
- Approved cavity wall installation work is guaranteed for 25 years.