Cavity Insulation

Save on your Energy Bills with Cavity Wall Insulation: A guide to cavity wall insulation

What is Cavity Wall Insulation?

Cavity wall consists of two parts, which are separated by a hollow space. These walls are built using masonry materials, such as cinder block or brick. The masonry material is absorbent and can draw humidity or rainwater into the wall.

Compared to solid walls, these walls have better thermal insulation. The empty space between the two walls reduces the transmission of heat into the building from outside. Cavity walls do not allow moisture content from the outer atmosphere to enter the house.

However, while it is very effective to stop cold and hot air coming from the outside, research has shown that 35% of heat loss from UK homes, occurs due to cavity walls. As a result, you have higher energy or power bills. Most homes that were built after the 1930s have cavity walls. The purpose was to keep moisture, humidity, or rainwater from getting in. However, this also led to heat loss between the two walls.

Therefore, it is important to insulate cavity walls to increase power efficiency in your home. This article is a basic but essential guide to cavity wall insulation.

Cavity Wall Insulation

Mineral wool is the insulating material used to insulate cavity walls. The installation involves drilling small holes into outside walls and then blowing the mineral wool into the gap until the cavity is completely filled.

The insulating material that has been injected or sprayed into the cavity traps the air. This also traps warm air and prevent its circulation. Thus, the heat loss is prevented by both conduction and convection.

The mineral wool insulating material is also available in slabs and you can use it to fill a cavity wall – both partially and fully. Phenolic boards and Polyisocyanurate (PIR) are other types of material available to insulate your cavity walls.

Most cavity wall installation companies in the UK provide CIG and CDGC guarantees of 25 years. Remember, the insulation of cavity walls will usually last longer than this.

Types of Insulation Materials

Mineral Wool Fiber
Mineral wool fiber is the most common type of material used for cavity wall batts insulation projects. The material is made from stone, slag, and molten glass. Manufactures melt these compounds, spin them, to produce fibers. The mineral wool insulation material is also available in the form slabs, which are used to partially or fully fill the cavity.

Polyisocyanurate (PIR)

PIR is made from thermoset plastic. This material is often regarded as rigid thermal insulation. You can use PIR boards to partially fill your cavity walls. Experts recommend using an R-value of 5.6 per inch of the foam thickness.

Phenolic

The manufacturing process of phenolic boards involves the formation insulating core by a plastic form between the two tissue face layers. Phenolic boards have fine cell structure and higher closed-cell content, which are used to partially fill a cavity wall.

Pre-Installation Inspection

If your home was built in the last 20 or 30 years, the walls are probably insulated. How to check whether your cavity walls are insulated or not? Hire a registered installer to carry out the process of borescope inspection. The professional drills a small hole in the outside wall and determine if the wall is filled or hollow. You can also check your walls with the local building control department.

For cavity walls batts insulation, your house must meet the following criteria:

• Your house outside walls is unfilled cavity walls.
• The cavity is 50 mm wide and there is no rubble.
• The brickwork and masonry of your outside walls are in good condition.
• The walls are not exposed to humidity and rain.
• No risk of flooding.

It is important to carry out a survey in order to check whether the home and outside walls are suitable for the cavity walls insulation. A professional contractor or installer can do this job accurately because they have all the necessary knowledge and tools. After carefully examining the walls using and checking them according to the aforementioned criteria, the installer would be able to insulate your cavity walls using polystyrene beads or mineral wool.

In addition, if your home has uneven or narrow cavities, then, there is a risk of flooding. At the same time, it can be regarded as an exposed site. In this case, the installer will use polyurethane foam to fill the cavity. Remember, this material is more costly than the regular or standard cavity wall insulation material, but it must more effective.

The installer will also check your home’s internal walls for dam patches. If found, the insulation cannot be installed until the problem of damp patches is fixed. You can hire a specialist builder for damp prevention.

If the external walls of your home are joined to another house, then there is a need for inserting a cavity barrier. This way, your neighbors won’t be affected by the insulation. Moreover, if you are living in a flat, the insulation is not possible legally – until everyone living in the building makes an agreement with you to insulate your flat or the whole block. This is usually costly.

How to Insulate a Cavity Wall?

The Cavity insulation of your home’s cavity wall is not a daunting task. You can insulate the cavity wall by injecting the insulating material such as mineral wool into the cavity from outside.

You can do it as a DIY project or hire a contractor to get the job done for you. A professional usually drill holes in the outside walls to inject the insulation material through the holes. After this, the professional will seal the holes with cement. The contractor may use mineral wool or polystyrene beads as insulation material. Some contractors use polyurethane foam.

You need to drill 22mm small holes at intervals of around 1m in the outside wall. Then, blow the insulation material into the cavity. After the insulation material is blown or injected, you need to fill the holes in the brickwork. This way, you will barely notice them.

Experts recommend hiring a professional contractor to do the job – as some think that it can’t be done as a DIY project. A professional installer completes the insulation of cavity walls in 2-3 hours without making any mess.

The cavity closer acts as a seal, preventing external water vapour and damp from entering the cavity wall and the building, whilst also preventing heat from being lost through the gap.

Advantages of Cavity Wall Insulation

The primary advantages of cavity wall insulation are given below:

Heat Loss Reduction: Cavity wall insulation can reduce the amount of heat loss from the wall during winters through convection. The cavity wall insulation is just like putting a lid on a hot cup of tea.

Mold Prevention: Condensation can cause mold and you can prevent it by installing cavity wall insulation. The insulation restricts moisture from passing through the walls. Because the outer wall is porous, water can go through it. When you have cavity insulation installed, it will trap water in between and it will just run above the windows or run down the ground rather than going through the inner wall. Mold will not build up because there is no or lesser moisture.

Lower Energy Bills: with an insulated home, you can save more in power consumption because heat loss is reduced significantly. As a result, the temperature inside your home is warmer and thus, you don’t need to turn the heater on – as they use more power or energy – leading to higher energy bills.