Mark Group

Cavity Wall Insulation Frequently Asked Questions

What does the survey involve?

The survey will usually take between 30 and 45 minutes, depending on your requirements and the size of your property. (It is helpful for us if we meet the owner of the property, rather than a friend)

Our Technical Sales Advisor will check your property externally for condition and measure the wall areas. They will drill a small hole in the wall to inspect the condition and depth of the cavity. This hole is then filled with sealant. We will take some photographs and assess any potential access problems.

Our Advisor will then need to inspect any fuel burning appliances inside your property to assess ventilation requirements. It may be necessary for us to install an additional safety vent in some properties – this will form part of your quotation.

Once this is complete we will discuss the findings, answer any questions you may have and give you a quotation. We will complete the paperwork and arrange an installation date with you there and then; or if you need a little time to think about it, then our Advisor will give you a call a few days later.

You will be left with all the relevant paperwork and contact details in case you have any further queries.

What is a cavity wall?

Modern homes are generally constructed of two masonry (brick or block) walls, with a cavity (gap) of at least 50mm between them. This gap is more commonly referred to as ‘the cavity’ but may also be referred to as “the void” around your home. Metal or plastic ties join the two walls together.

This construction standard was widely adopted as building practice in the 1920’s. Before this, walls were generally built with two courses of brick interleaved together without a cavity (solid). Of course this date is only a general rule of thumb, as earlier and later properties can have cavities or be of solid construction.

What is cavity wall insulation?

Most people are aware of what loft insulation looks like. It is generally a mineral wool made out of either glass or rock fibres and is packaged into a roll. This is laid out like a quilt into the loft space. Cavity wall insulation is a similar product, made in the same manufacturing plants, within the UK, as loft insulation, but is specially treated with silicants and milled down in order for it to be blown into the cavity of your home. It therefore creates the same quilt-like effect as loft insulation but in the enclosed void around your home.

How will the cavity wall insulation be installed?

Our technicians will arrive at your home and perform a pre-installation check. They will arrive in a vehicle containing all the material and equipment required to carry out the work and complete the installation that day. In certain instances, a second team may be used to fit one or more of the measures in your home and in these cases the production planners will try to get the two teams to arrive on the same day.

The vehicle our teams will arrive in will be clearly marked with the Mark Group logo and the technicians will be wearing our distinctive red and blue uniforms. Please remember however to ask them for their identification cards.

Contained in each vehicle is a special built-in machine that will be used to prepare the insulation and inject it into your empty wall void.

The installation process is essentially in two parts. Firstly, the technician will drill holes in the mortar in-between the bricks of your home, at specific points around each elevation. These holes will be of 22 to 25mm in diameter and will be “made good” to the surrounding mortar after injection. This we call ‘the drilling process’.

Then a special pipe will be connected to the machine in the vehicle and cavity wall insulation material will be placed into that machine. The technician will insert the nozzle end of that pipe into the prepared holes and using his remote control, activate the machine to blow the prepared material into your cavity using air. This we call “the blowing process”.

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 blowing process will not cause any vibration as such but the machine makes a slight humming noise.

The technician will need to gain access to all walls, so he will need to get inside attached garages, lean-to-sheds, conservatories etc.

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.

Is there much mess?

The drilling process inevitably creates a little dust. The technician will go around the outside of your home at the end of the installation and clean up. It is important to note however, the conditions and nature of our weather can at times hamper even the most determined attempts. Please, take the time to speak with our staff and be sure that you are happy with the finished product. We also believe it wise to remove vehicles from the drive and items close to the walls. In return this will give the technician better access 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 inside 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 (the dividing wall between your two properties). This is usually a length of bristle brush. Of course, if the neighbour’s house were to be insulated at the same time, or has already been insulated, the cavity barrier will not be needed.

How do I know the walls are full?

This system of cavity wall insulation has a defined pattern of holes, which has been tested by the British Board of Agrément to verify that it results in a complete fill. The equipment used in the blowing process has an automatic cut out, which actuates when the adjacent wall area is full and the pressure builds back up from the injection. There is also tolerance in the injection pattern so that the material will flow past the next injection hole.

It is well proven for our technicians and inspectors to check the holes have been placed where required and that the fill is adequate. Also, during your survey, we took measurements of your home including a depth gauge and inspection of the cavity to be filled. From these measurements we know the amount of material required to correctly fill your walls. The Technician will therefore check and record this data and match this against the quantity of insulation used. Our internal office staff operate a 100% check of this data and measure your results before we issue your 25 year guarantee.

It is possible that you may also be randomly selected in our on-site technical monitoring.

Note: Drilling a hole in the outer wall and testing the cavity fill with a rod or pencil will not provide any meaningful information. If in doubt, please contact our customer services team.

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 redundant, such as cavity vents or vents that are in bedrooms may be closed off. The technician should discuss these with you, so if you have any questions please ask. Redundant airbricks may be filled.

What about filling the holes?

The technician will fill all the injection holes with mortar that closely matches the existing colour and texture. On some older properties or weathered facades it may take several months for the newness of the mortar to blend, but these holes are very small and they will blend as the weather effects them. On pebbledash finishes, they will apply pebbles to the surface to match the existing finish, as close as possible.

But my house has painted areas?

Normally, we 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 necessary for you to consider painting the area, after the mortar has dried.

When will I receive the guarantee?

The guarantee you will receive is called a “CIGA” named after the agency that issues them (Cavity Insulation Guarantee Agency). It is an independent guarantee for a period of 25 years. We will apply for it on your behalf and it will be sent to you direct from CIGA. It can take up to 8 weeks for this to be delivered to you after installation. CIGA is non-profit distributing; its only function is to stand as guarantor for the promises set out in the guarantee. It has the resources to meet the promises made in the guarantee.

Will my house be warmer?

Insulation dramatically reduces heat loss through the insulated wall or ceiling to the other side. So the answer to the question is yes.

However, if your heating has a thermostat, it will cut out the heating at the same temperature, so you may not notice it being warmer in the same room as the thermostat, it will be the desired warmth.

You should find though, that the temperature in other parts of your house improves. It is because the house will retain its temperature for longer, therefore the time between heating cycles may also be longer. The result should be a more even temperature throughout the house and/or a reduced fuel bill.

It is also important to note the insulation will have an effect during the summer. You will no longer be generating heat inside the house from your heating system but the insulated wall will prevent some of the heat generated by the sun from entering through the walls into the house, keeping your home cooler.

Are there any maintenance or servicing requirements?

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

How much energy will I save?

You will save around 1 tonne of CO2 per year, and up to £160 per year on your energy bills.

Source: Energy Saving Trust.

If I am concerned after the installation - what should I do?

Talk to us to discuss your concerns and allow us an opportunity to investigate your worries. Most concerns can be resolved swiftly and efficiently so please do not hesitate to speak to a member of our customer services team.

How long will the insulation last?

For the life of the building – the BritishBoard of Agrément say so.

How long does it take for Cavity Wall to be installed?

No property is the same, however for the main house types, the following can be given as approximate guidelines:

• a 2 – 3 bed Semi Detached house below 90m2 would take a 2 man crew between 1hr 30 to 2hr 30
• a 3 – 4 bed detached house below 140m2 would take a 2 man crew between 2hr to 3hr 30