Cavity Wall Insulation

What Is Cavity Wall Insulation?

Cavity wall insulation involves filling the gap between the two layers of a wall that are separated by a hollow space or "cavity." Typically, this is done in homes built with two layers of brick or block walls to prevent heat from escaping and cold air from entering, thus improving energy efficiency. 

The materials commonly used for cavity wall insulation include mineral wool, foam, and polystyrene beads. Each has its properties and suitability depending on the specific requirements of the building and local climate conditions. 

Besides the obvious benefit of energy saving, cavity wall insulation can also help reduce condensation inside the house if it's installed correctly. 

However, it's crucial to ensure that the home is suitable for this type of insulation. Factors like wall condition, exposure to driving rain, and existing damp issues need to be considered, as improperly installed or inappropriate insulation can lead to problems like damp or mould growth.

How Does Cavity Wall Insulation Work? 

Cavity wall insulation works by creating a barrier between the inside and outside of your property, which helps to keep heat in and cold out. 

This not only helps in reducing heating costs but also minimises the carbon footprint of the home by lowering energy consumption. 

The Energy Saving Trust notes that in an uninsulated house, walls account for about 35% of heat loss. Given that walls are the source of roughly one-third of heat escape in such buildings, installing cavity wall insulation is a clear choice for anyone looking to significantly reduce heat loss and lower energy costs.

Cavity Wall Insulation Benefits 

• Enhanced energy efficiency
• Reduced heating and cooling costs
• Improved indoor comfort
• Minimised heat loss
• Lower carbon emissions
• Noise reduction
• Prevention of dampness and condensation
• Increased property value
• Eco-friendly home improvement

Cavity Wall Insulation: Partial Fill vs. Full Fill

Partial-fill cavity insulation involves leaving a 25mm or 50mm gap between the insulation material and the external leaf of masonry walls, reducing the risk of moisture damage to internal structures and is often required by local authorities for new builds. 

In contrast, full-fill cavity insulation offers a quicker and easier installation process by fitting snugly between masonry walls without the need for securing boards or slabs, effectively reducing heat loss and preventing problems related to mortar debris in the cavity space. However, it's important to note that not all buildings are suitable for cavity insulation depending on local building codes.

Types of Cavity Wall Insulation Material

Understanding the different types of cavity wall insulation is crucial for enhancing a building's energy efficiency and comfort. Each material and insulation approach offers unique benefits and considerations. 

Mineral Wool Cavity Insulation

Made from natural rock or slag, mineral wool insulation is fibrous, allowing it to trap air and provide effective thermal and acoustic insulation.

• Benefits: It is highly fire-resistant and does not degrade over time, ensuring long-lasting performance. Additionally, it is resistant to moisture and can help prevent mould growth.
• Considerations: The density of mineral wool can make it heavier than synthetic insulations, requiring careful installation. It’s also important to ensure it's packed well to avoid settling or gaps.

Polyisocyanurate (PIR) Board Insulation 

PIR boards are rigid foam panels that offer excellent thermal insulation. They are composed of a polyisocyanurate polymer and are often faced with aluminium foil on both sides.

• Benefits: PIR boards have a higher insulation value per inch than many other forms, making them ideal for achieving significant energy savings. The foil facing provides a moisture and vapour barrier, enhancing their durability.
• Considerations: While effective, PIR can be more expensive than other insulation types. Installation must be precise to avoid thermal bridging and ensure airtightness.

Phenolic Foam Boards

Phenolic boards are made from phenolic resin, creating a rigid panel with fine, closed cells.

• Benefits: It offers superior insulation properties and excellent fire resistance, performing well in both regards compared to many other insulation materials. Phenolic foam also has a low thermal conductivity, making it highly efficient.
• Considerations: Phenolic foam tends to be among the more expensive insulation options and requires professional installation to ensure optimal performance.