The ultimate guide to cavity wall insulation
Dyson Energy Engineer

Cavity Wall Insulation

You could be eligible for FREE cavity wall insulation*

Heat will always flow from a warm area to a cold one. In winter, the colder it is outside, the faster heat from your home will escape into the surrounding air. In general, houses built from the 1990s onwards have wall insulation to keep the heat in, but if your house is older than that it may not have any wall insulation. If this is the case then you may be losing a lot of heat from your home, as heat can escape more quickly through uninsulated walls. Most types of wall can be insulated in one way or another. If you have a typical house with cavity walls, you could save up to £155 per year (based on a semi-detached house) in heating bills just from insulating the walls. The first thing you need to find out is what sort of walls you have.

So what is Cavity Wall Insulation?

Most homes built after 1935 will be constructed with a masonry cavity wall. This is where there is a gap between your internal and external wall which can be filled by drilling a series of holes and pumping in either mineral wool or a polystyrene bead. The work only takes around half a day to complete. Homes built after 1995 should already have adequate levels of insulation in the cavity.

How to check if your house already has cavity wall insulation

If your house was built after the mid-1930s, chances are it has cavity walls. To check, have a look at the outside of your house:

  • Measure your window sills, if they exceed 10 inches, you probably have cavities
  • You can also tell by looking at the brick pattern.  If your home has cavity walls, the bricks will all look the same size, whereas if your walls are solid and therefore unsuitable for cavity wall insulation, every other brick will probably be placed end-on.

Once you’ve established that your house does in fact have cavity walls, the next step is to check whether or not they’re insulated.

Cavity wall insulation works by filling the gap between your internal and external walls with an insulating material, which helps to keep heat in and reduce your energy bills. There are two main types of cavity wall insulation –

If there is a drilling pattern within the mortar joints on the external walls of your home, this usually is a good indicator that your home has been insulated.  The drilling pattern will vary depending on the type of insulation material used to insulate your walls.

For example, if your home has been insulated with mineral wool, typically the drilling pattern on the front of your house will look like the below:

Mineral wool cavity wall insulation brick pattern

The drilling pattern is different if your home has been insulated with polystyrene bead insulation, typically like the below:

Cavity wall insulation brick pattern for ThermaBead

If you’re still not sure, you can contact Dyson Energy Services, a professional insulation company or surveyor to come and take a look for you. They have special tools such as a borescope that can allow them to drill a small hole in the mortar and view the cavity.

How do I get free cavity wall insulation?

If you or a member of your household is on a qualifying benefit, you may qualify for free cavity wall insulation through the government Energy Company Obligation (ECO) scheme.

Check out our funding page for further details, on the insulation grants available.

New government driven standards

New government driven standards, that came into effect from the 1st of July, mean that householders who sign up to funded energy efficiency measures through the Energy Company Obligation (ECO) scheme, will benefit from a new requirement to install additional ventilation in their homes, where required.

What are the benefits of cavity wall insulation?

  • Savings on your energy bills
  • Warmer home in the winter, cooler in the summer
  • Increases the value of your property
  • Helps to reduce your carbon footprint.

How much money could I save?

According to figures from the Energy Saving Trust website, cavity wall insulation could save on average £155 per year (based on a semi-detached house).

“We have to do our bit for future generations”

Neil and Karen, a couple from Somerset, recently had cavity wall and loft insulation installed, which was funded through the Energy Company Obligation scheme and installed by Dyson Energy Services.  They were keen to tell their story in the hope that it encouraged others to benefit from energy-saving insulation too.

Read their story.

Do you need more information?

Frequently asked questions

Read the frequently asked questions from our customers below.

Is my house suitable for cavity wall insulation?

If your house was built after the 1920s, it is likely to have cavity walls. Older houses (pre-1920) are more likely to have solid walls, with no cavity and possibly no damp proof course.

Before the installation, one of our retrofit surveyors will carry out a free no-obligation assessment of your property to confirm that it is suitable for insulation. Once it has been confirmed, the survey will be uploaded to the IAA (Insulation Assurance Authority) where they will complete an independent inspection to confirm suitability and consumer protection. Once the property has been independently deemed suitable for retrofit cavity wall insulation, a member of our team will contact you to arrange a date for install.

How is cavity wall insulation installed?

Retrofit cavity wall insulation is injected with insulating material by drilling holes through the mortar joint of the external leaf. The drill holes are 22-26mm in diameter, dependent on the material used. The holes are then made good after injection. Each hole is injected in turn.

I have vents at my property. What will your installers do with these?
Any ventilators supplying air to gas appliances will be safeguarded by installers. This would be the same with any underfloor ventilation. The installers will check to see if these are suitably sleeved.

How long does it take to install cavity insulation?

Cavity wall insulation can be completed within 2 to 4 hours. However, this will depend on the size of the house and access around the property.

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

Our installers will insert a cavity barrier at the party wall line if your neighbour’s property is uninsulated. If your neighbour’s property is insulated, no barrier would be required.

What about filling the holes?

Our installers will fill all the injection holes with mortar to match the existing as closely as possible.

What products do you install?

We install either a bonded bead or white wool fibre products which are both systems of cavity wall insulation that have been tested, assessed, and approved by the British Board of Agrement (BBA) and KIWA.

Are your installers employed by you?

Yes.  Our professional employed teams are trained to the highest standards.

Will cavity wall insulation cause damp?

Cavity wall insulation does not cause damp, however, it can exacerbate an existing problem, if not picked up correctly during the initial survey.

To reduce the likelihood of damp in your property, it is important to maintain exterior brickwork, rainwater goods and rooflines to protect your home from severe wind and rain. At the survey stage, our experienced Surveyor will check your cavity using various equipment to ensure there are no existing damp problems and that it is suitable for cavity wall insulation. The bonded bead product, which we use to insulate cavities, by design does not allow water to track against the system, therefore reducing the risk of damp.

  • *Subject to qualifying criteria, property suitability and funding

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