Cavity Wall Insulation

35% of all heat leaves the home through the walls

Heat travels from high temperatures to lower temperatures, so the lower the temperature outside, or the poorer the insulation, the colder your home will be.
As a general rule homes built in the last twenty five years will be insulated in one way or another, but if your house is older than that it is almost certainly going to be an empty cavity, or a solid wall with no insulation. Should you not have any insulation then you’ll certainly be losing considerable amounts of heat as a cavity walls is not all that efficient. Most standard properties with cavities can be insulated and normally you’ll save up to £150 per year in heating costs from the process and only second in importance to loft insulation and considerably more valuable to the home than sash window draught proofing. The very first step will be to make sure you fully understand what wall you have and what insulation, if any, is in place.

Typical solid brick walls or with a cavity.
Almost all homes in the UK have cavity or solid walls.

• A cavity wall is a simple two skin brick arrangement, known as the cavity with the outer skin always brick and the inner skin brick or concrete. Victorian properties will almost always be two skins of brick with a cavity.
• A solid wall simply has no cavity and is easily identified by a half brick face showing. It’s actually a lot less common that cavity walls.

cavity wall or solid


Once you know your brick wall type what to do next.

Commonly you’ll find most properties constructed after 1920 will have a solid wall. Before that, and very commonly in London from the Victorian era, you’ll have a cavity wall.

Regular brick patterns as can be seen in the image below are normally cavity. It’s not safe to make this type of arrangement for a solid wall.

If the walls are solid then they will have half brick after every whole brick. The two arrangements are extremely easy to spot.

In some cases your wall may be covered with render or pebble dash. Walls can be measured as it’ll give away the arrangement of brick. Any wall over 27cm in thickness will like be cavity as it’s beyond the length of a standard red brick. Stone walls can be up to 1 metre in thickness and still be solid.

What if my walls aren’t cavity or solid?

Modern builds can be steel or wood frame. This isn’t necessarily a problem and it’s quite likely your property is already insulated well. There’s also the possibility your walls are prefab concrete and then you’ll need to insulate using different methods. This type of wall will normally be insulated internally behind the plasterboard, effectively an extra layer attached inside the property. This method may not be cost effective as you need to install new plasterboard, the insulation, plaster, and then decorate. Take a look at the picture below to see how it’s done. There’s every chance your home is already well protected.


What’s cavity wall insulation and is it suitable for my home?

Cavity wall insulation is most typical in cavity walls of buildings built after 1920. Very commonly council housing built in the 60s and 70s are ideal for this upgrade, keeping the warmth in to save energy. It will considerably improve condensation and dampness in properties that have issues with the external brick. Cavity wall insulation is forced into the gap with high pressure and fills the void entirely. If it does not fill entirely then the effectiveness is reduced. It’s important to keep spacing of holes drilled to apply cavity insulation reasonably close to ensure a good install.

There’s a few obvious property types that are idea for cavity insulation and they are listed here:

• If external walls have a cavity
• The cavity itself is larger than 5 cm.
• If the brickwork is structurally sound then it lends itself to the install
• Homes older than twenty five years which would not of had modern regulations on insulation enforced.
• Walls that are not continually damp from rising issues or rain.

It your still unsure then ask for a boroscope inspection.

Properties with rising damp, or general damp patches are not ideal for cavity wall installation and the damp issue itself must be solved prior to insulation. The damp will cause the foam to perish and lead to further issues. Interestingly, if your property is terraced then an additional consideration is that a blocker should be installed to stop foam penetrating the gap of your neighbours.

What materials are used?

Cavity wall insulation is normally a foamed insulant but can also be made of mineral wool or polystyrene beads. The most common installation is a foam. All methods will be manufactured to strict British Standards, irrespective of the material chosen.

material for cavity wall

How is insulation installed?
To insulate your cavity walls, the installer drills small holes around 2.5cm in size at intervals of around 1m in the outside wall of your home.

A professional can do the job in around two hours for an average house with easily accessible walls. It shouldn’t make any mess.

Something went wrong with my installation.

If there’s a problem with the cavity wall installation then the best thing to do is call the original installer first. It’s not unheard of that an issue will arise and normally the company who installed will be happy to put the problem right. The normal procedure would be to pop around and discuss the installation requirements and if that was met to standards, or if a new issue has been made by the install itself. If the fault lay with the cavity wall insulation company they will take responsibility and put right any issues that have occurred. If they believe they are not at fault then do not worry, you still have your 25 year guarantee to levy upon. This brings us to an important point. Please make sure on completion you have a CIGA guarantee certificate to protect yourself from future problems.

It should be noted that a poor insulation job is equally as likely as a lack of maintenance and there are a whole host of reasons as to why your experiencing issues. If you feel the installer is at fault and has not done the best to remedy or even help then you should follow the complaints procedure to have an unbiased, independent body look over the fact and assist in making a fair decision. If you decide to remove the cavity wall insulation then please use an accredited installer.