What is the cost of Cavity Wall Insulation

Before starting a cavity wall insulation project, property investors should decide on the best insulation material for their property. This choice impacts the overall cost of cavity wall insulation.

So, what are the different materials available, and what are their pros and cons?

Mineral wool, used since the 1950s for cavity wall insulation, is derived from igneous rocks. It can also be made from recycled glass or sand.

Pros: Mineral wool is an eco-friendly insulation choice, readily available and budget-friendly. It’s easy to install and offers good efficiency, making it a practical option.

Cons: Mineral wool insulation needs a clear and roomy cavity, which might involve costly cleaning and professional help. Not suitable for small spaces, it could lead to problems like clumping and dampness, potentially harming a property’s structure or causing cracks in the building’s rendering.

Costs (approx. excluding labour): £10-15/m²

Polyurethane foam, or PUR, is commonly used in newer buildings. It’s created from carbon-based organic units that join together to form a polymer.

Pros: Polyurethane foam, or PUR, is the best material for insulation as it efficiently keeps a property warm and is cost-effective. Unlike mineral wool, PUR doesn’t retain moisture, preventing the formation of mould in a property.

Cons: Polyurethane foam, or PUR, may shrink over time, creating gaps that allow water to enter the building.

Costs (approx. excluding labour): £20-25 to install Polystyrene beads

Expanded polystyrene beads, or EPS, are carbon polymer-based insulation installed in a property’s walls using a bonding agent.

Pros: EPS is durable, lightweight, and easy to install, making it a cost-effective choice for cavity wall insulation. It is resistant to water and recyclable, adding to its appeal.

Cons: Again, a clean, spacious cavity is necessary for EPS insulation, which can increase costs. Moreover, gaps can appear in the cavity when using this material, especially if the bonding agent starts to wear. As such, mould and dampness can occur, while heat might begin to escape.

Costs (approx. excluding labour): £10-15/m²

Cavity batts, made from compressed mineral wool, are commonly used in new builds and have been around for about 30 years. They come in slabs of different thicknesses, typically ranging from 50-150mm.

Pros: Cavity batts are light and easy to handle, less prone to clumping than regular mineral wool, reducing the risk of damage. They should be installed close to the inner wall, leaving space for ventilation and preventing water buildup, minimizing the risk of dampness. They are also rated A1 for fire safety, making them a safe insulation choice.

Cons: However, it is not necessarily the best insulation material, and can only be installed in the process of building a property.

Costs (approx. excluding labour): From £6/m² (50mm thickness) up to £16/m² (150mm thickness).

Insulating a property typically costs around £200 per two-storey wall. For mid-terraced houses with only two external walls, the cost is on the lower side, approximately £400.

Detached properties can cost around £800 or more for cavity wall insulation, while bungalows, being shorter, are usually cheaper at around £400.

Having explored the costs of different cavity wall insulation materials, let’s delve into the potential annual savings these installations could bring.

The following table provides estimates from the Energy Saving Trust, reflecting average savings in gas-heated properties without subsidized insulation installations.