How much will I save?
Insulating your walls is very important – around a third of the wasted heat in an un-insulated home is lost through the walls. Insulating your cavity can save up to 40% of this wasted heat. Installing cavity wall insulation can save up to £135 off your heating bills every year, and costs in the region of £100 to £300 with discounts from fuel companies. It also saves around 550 kg carbon dioxide emissions every year. The Energy Saving Trust gives more details on costs, savings and payback time. If all the houses with unfilled cavity walls had them filled, the energy saved could heat 1.4 million homes each year.
Cavity wall insulation has to be carried out by a specialist contractor who can provide a CIGA (Cavity Insulation Guarantee Agency) certificate guaranteeing the work for 25 years. The local registered member company is Heatex Group of Stoke on Trent.
Obviously you can only have cavity wall insulation if your house was built with a cavity to fill. A cavity is a gap between two skins of brick, or a skin of brick on the outside, and blockwork on the inside. The two skins are held in place by wall ties. Houses built from the 1930s onwards generally have cavity walls, although many 1930s houses in Stafford were built with solid walls.
A cavity wall has all the bricks placed lengthways, (stretcher bond) whereas a solid wall has some bricks placed end on (headers). It is less easy to tell with rendered houses, but houses built with cavities have thicker walls than solid wall houses, as the cavity is usually about 50mm (2 inches) wide. 
By 1983 houses were being built with insulated walls, so any house built after this date will not need cavity wall insulation. Many modern houses are timber framed, even if they have a brickwork outer face, and cannot be cavity wall insulated.
How is the insulation installed?
The contractor injects insulating material into the gap between the two skins of brickwork, through holes drilled at regular intervals into the mortar joints. The work causes little or no disruption as the insulation is injected into the cavity from the outside, typically taking two or three hours. The holes are then filled with mortar or render to match the existing. As well as massively decreasing the amount of heat which escapes through the walls, it reduces draughts and will help create a more even temperature in your home, help prevent condensation on the walls and ceilings and can also reduce the amount of heat building up inside your home during hot weather.
Grants
Funding is available from fuel companies so that installers can cover the full cost of insulation for households on benefits and older people. Anyone over 70 can have free insulation. However any household is entitled to substantial discounts. Currently a typical semi-detached house can have cavity wall insulation installed for only£149.
Important Points
- The contractor will do a pre-installation inspection to check that the walls are suitable. Make sure that your house has cavity walls, and that they have not already been filled, (look for signs of holes in the mortar which have been filled) but if you are not sure, the contractor will check this first.
- Cavity wall insulation does not increase the risk of dampness, but any damp or structural problems must be cured before the cavity is filled, for example pointing, failed damp proof course, debris in the cavity, failed wall ties, cracking, or condensation caused by poor ventilation.
- If you live in a semi-detached or terraced house, the contractor will install cavity barriers to prevent the insulation entering the cavities of your neighbours – or get them to have cavity wall insulation at the same time! Generally blocks of flats all need to be insulated at the same time.
- A conservatory may make insulation difficult on that wall – but ask the contractor for advice.
- Very exposed walls, or walls in properties over 12 metres high, may not be suitable for insulation.
- The material used for cavity wall insulation is generally mineral wool, polystyrene beads, polyurethane or Urea formaldehyde foam. If an installer is unable to carry out the work because of unusual conditions, it may be worth contacting a contractor who uses one of the other insulating products.
- Once installed, the contractor should check that that the filling has been done correctly, for example that there are no gaps in the insulation.