Cavity Wall Insulation – FAQs

What is cavity wall insulation?

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


How is cavity wall insulation installed?

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 from the bottom.


How long does it take?

Cavity wall insulation normally takes around two hours to install, but the time does depend on the size of the house and other factors, such as access.


Is my house suitable?

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 of the technician before installation.


Do I have to do anything before the 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 the walls, so they 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 your boundary, you may like to mention to your neighbour, that the technician will need to go onto their property.


Is there much mess?

The drilling process inevitably creates a little dust, which will be cleared at the completion of the job. It may be wise to remove vehicles from the drive and things close to the walls. This will also give the technician better for equipment and tools.


Does the technician have to come into the house?

The technician must undertake checks before and after installation, including any heating appliances, so it is essential that they have access to the property.


My house is semi-detached, how do they stop insulation going into my neighbour’s cavity?

Assuming your neighbour’s house is not already insulated, the technician will insert a cavity barrier at the party wall line. this is usually a length of a bristle brush. Of course, if the neighbour’s house were to be insulated at the same time, the cavity barrier woudl not be needed.


Are all the systems of insulation the same?

There are several different types of insulation:

  • Bonded bead (white polystyrene beads)
  • Glass wool (yeallow or white in colour)
  • Rock wool (grey/brown in colour)
  • Urea formaldehyde foam (white foam)

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

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

Except for Urea Formaldehyde foam, the systems can be used in all parts of the UK.

All systems have a similar insulation value.


Are the technicians trained?

All technicians (team leaders) undergo training by the systems supploer and the installing firm to ensure they are competent in CWI and carry a training card. Please feel free to ask to see the training card.


How do i know the walls are full?

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 patter so that the material will flow past the next injection hole.


Is the insulation dense?

No, as the insulation is contained within a masonary wall, it doesn’t need to be ‘dense’. For insulation and other purposes, a light density is better. Before installation, the technician will undertake a quality test to ensure the insulation will go into the wall at the right density. He will also note the amount of material used, the know that sufficient insulation has been installed.

Note:drilling a hole in the outer wall and testing the cavity fill with a rod or pencil will not provide any meaningful information.


What about the ventilators that are in the external wall?

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 redundent, such as 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. Redundent airbricks may be filled.


What about filling the holes?

The technician will fill all the injection holes with mortar to match the existing as closely as possible. They will user a mix that closely matches the existing colour and texture. On pebbledash finishes, they will apply pebbles to the surface to match the existing finish. After weathering, the holes are difficult to see.


What if my house is painted?

Normally, the installing firm will not paint the injection holes. Unfortunately, even if the original paint is used, it may not match due to weathering. So it may be neccessary for you to consider painting the area, after the mortar has dried.

You should discuss and agree what will be done, with the installing firm.


Do I apply for the CIGA 25 year gurantee?

No, the installer or the agent submits the gurantee application. The gurantee is posted to you within days of the application being received at CIGA – KEEP IT SAFE.

CIGA is non-profit distributing; its only function, is to stand as gurantor for the promises set out in the gurantee. It has the resources to meet the promises made in the gurantee.

All proffessional approved installing firms are members of IGA and can apply for a CIGA gurantee, for properties built with traditional cavity walls. You should insist on a CIGA gurantee, since nothing else can give you the level of assurance to which you are entitled.


Will my house be warmer?

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, therfore 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.


Are there any maintenance or servicing requirments?

No, not to the cavity wall insulation, but normal building maintenance is needed.


How long will the insulation last?

For the life of the building – the British Board fo Agrement say so.


If I am concerned after the installation what shoudl I do?

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

They will help you.