Cavity Wall Insulation

Get the answers you need to make a decision on cavity wall insulation. Find out if it’s suitable for your home.

Most houses built after the 1920s have cavity walls. However, in the last 20 years, it’s become standard practice to fill these cavities with an insulating material. So if your home is older than 20 years, it’s likely that you are loosing a large portion of your home’s energy bill through these empty spaces. Adding insulation is an efficient solution to reduce your energy bills and preserve heat inside your home.

What’s In This Guide?

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Cavity Wall Insulation Costs

For a 3 / 4 bedroom semi-detached house the cost is between £600 – £ 1000. This works out at about £7.50 – £10.50 per square meter.

Cavity walls are one of the easiest ways for heat to escape from your home. Sometimes up to 1/3 of the heat can be lost this way. Therefore, by installing cavity insulation, you can save between £200 and £300 per year on your heating bills. According to statistics, the investment in cavity insulation can pay off over 3 years or less.

Cavity Wall Insulation Savings & Grants

SEAI Grants

Cavity wall insulation grants from Sustainable Energy Authority the UK are available to reduce the costs of installation and encourage homeowners to make the leap. There are also grants available through Electric the UK’s Energy Efficiency Initiative.

What Are Cavity Walls?

Cavity walls are usually built of brick and consist of two thin walls separated by a gap (or cavity) with metal wall ties holding them together.

Types Of Cavity Wall Insulation

The most common type of material used in the UK is a type of polystyrene bead system. But there are other options.

Polystyrene Beads – These granules can be used in their loose form or in a sticky resin which helps them bind together. They are blown into the cavity using compressed air.

Blown Mineral Fibre – Fibre made of rock wool or fibreglass is blown into position via specialised machine.

Urea Formaldehyde Foam – A foam is created by mixing two chemicals and injecting or spraying it into the cavity. This foam then expands filling the space.

How to Determine If You Have Cavity Walls?

There are several ways to check your homes walls and they should be used together to decide. Don’t just rely on one test.

Building Age

First of all, the age of your house is probably the best indicator. Houses built before the 1920’s were generally built without cavities. And houses built within the last 20 years generally have insulated cavities.

Check The Brickwork

But, if you are not aware of the age of your house, you can check the visible brickwork to get a clue. If the walls in your building have cavity gaps, the size of each brick will be the same making a regular pattern (as seen in 2 below). On the other hand, if the size of the bricks differs with every other brick placed end-on, it means that the wall is solid (picture 1).

Wall Thickness

Another way to tell if you have cavity or solid walls is to check the thickness of the walls. It can be useful in case your brickwork has been faced with another material. Take a look at the doorways and windows. If a brick wall appears 12 inches thick, it’s an indication that you probably have got them.

Boroscope Inspection

If you are still unsure whether you have cavity walls, you can contact a registered installer to conduct a boroscope inspection. The installer drills a small hole into the wall to check suitability.

Local Planning Office

You can also contact your building control department or local planning office which should have the records of work performed on the building, including the wall insulation.

Insulation of Non-Cavity Walls

If the walls in your house are made of solid stone, there will be no cavities to insulate. In this case, you’ll need to investigate other ways of insulation such as external wall insulation.

Whilst timber or steel framed homes are not common in the UK, there are some and these won’t be suitable. If you are suggested to install cavity insulation between the outer bricklayer and the timber frame, it’s recommended to refuse it because it can cause severe damage to your house.


What Houses Are Suitable

When you’re considering wall insulation, you have to make sure that your house meets specific requirements. First of all, the walls have to be made of brick and have an unfilled cavity between the layers which is at least 2 inches wide. Make sure that the brickwork is in good condition. The external walls of your house should be easily accessible. If your walls are joined to the house of your neighbour, a cavity barrier will have to be inserted, and that can slightly increase the cost. Also, the installers sometimes refuse to work around garages or extensions.

Another requirement is that your home must not be taller than twelve metres, which is about four storeys. You have to ensure that your walls are dry because wet insulation can be harmful. So, if you spot any leakage in your walls or damp patches, you have to fix the damage before installing insulation. If your walls are exposed to rain very often, cavity insulation may not be the best choice for your house. Also, cavity insulation won’t be suitable for a house if it has steel or timber framed construction areas.

If your house meets all the requirements mentioned above, then it is suitable.

Energy Savings

When you decide to improve your home’s energy efficiency, cavity wall insulation is a great place to start and when paired with spray foam insulation of the attic or loft and double glazed windows, you’ll have an energy efficient home that is both comfortable and cheap to heat. And coupled with a modern boiler you will see significant savings.

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