The external wall of a house is constructed of two masonry (brick or block) walls, with a cavity (gap) of at least 50mm between. Metal ties join the two walls together.

The cavity wall is injected with insulating material by drilling holes in the external wall, through the mortar joint. Holes are generally of 22-25mm diameter and are ‘made good’ after injection. Each hole is injected in turn, starting at the bottom.

Before the installation, the installing firm will undertake an assessment of your property to confirm that it is suitable for insulation. This assessment may be undertaken by a surveyor or the Technician before installation.

The drilling process does create some vibration – so it would be wise to remove ornaments, particularly on external walls, for their safety and your peace of mind. 

The Technician will need access to all walls, so he will need to get inside attached garages, lean-to sheds, conservatories etc. The insulation can only be really effective if all walls are done. If you have a wall right on the boundary, you may like to mention to your neighbour, that the Technician will need to go onto their property.

There are several different types of insulation:

• Bonded bead (white polystyrene beads)
• Glass wool (Yellow or white in colour)
• Rock wool (Grey/brown in colour)

Note: both glass wool and rock wool are known as ‘mineral wool’.

All systems of CWI have been tested, assessed and approved by the British Board of Agréement or the British Standards Institution. All are suitable for their purpose.

All systems have a similar insulation value.

Each system has a defined pattern of holes, which has been tested to verify that it results in a complete fill. Most systems have an automatic cut out, which actuates when the adjacent wall area is full. There is tolerance in the injection pattern so that the material will flow past the next injection hole.

Ventilators supplying combustion air to fuel burning appliances must be safeguarded. Similarly ventilators at ground level that ventilate below timber floors must be safeguarded. The Technician will investigate them to check they are already sleeved. If they are not, the Technician will remove them and seal around them to stop them being blocked by the insulation. Other vents, which may be redundant, such a cavity vents or vents that used to supply air to open fires in bedrooms may be closed off. The Technician should discuss these with you. Redundant airbricks may be filled.

For the life of the building – the British Board of Agreement say so.

Yes – if your heating is not controlled by a thermostat. However, if you have a thermostat, it will cut out the heating at the same temperature, so you may not notice the difference in the room with the thermostat. However, you should find that the temperature in other parts of your house improves, for example, the small bedroom on the corner.

With CWI, you should find that the house holds its temperature for longer, therefore the time between heating cycles may be longer. The result should be a more even temperature throughout the house and / or a reduced fuel bill.

Talk to the installing firm and tell them of your worries. A contract exists between you and the installer, so they must be given the opportunity to investigate your worries.

They will help you.