A Guide to External Wall Insulation for Houses

External wall insulation is an effective way to improve energy efficiency and create a more comfortable living environment at home.

This guide looks at external wall insulation in detail, including its benefits, the different materials available, the installation process, and the costs involved. It also highlights funding options that could help cover the expense.

Why insulate the external walls of your home?

External wall insulation (EWI), also called external solid wall insulation, involves attaching insulation to the outside of your walls. Two main layers are applied:

• An insulation layer.
• An outer layer of mineral or synthetic render for weather protection and appearance.

Depending on the thickness of insulation used, installation typically adds around 100mm to the exterior of your home.

Insulating exterior walls is one of the most effective ways to boost your property’s energy efficiency. It reduces heat loss in winter, prevents overheating in summer, and can cut annual heating and cooling bills significantly.

Materials for external wall insulation

• Expanded polystyrene (EPS): Lightweight, cost-effective, and with strong insulating performance.
• Mineral wool: A natural, breathable material that also provides fire resistance and noise reduction.
• Phenolic foam: Offers high thermal performance with thinner layers, making it suitable where space is limited.

Installation process

External wall insulation should always be installed by qualified contractors and may require planning approval.

The process typically involves:

1. Assessing the property’s suitability and selecting materials.
2. Preparing the walls — repairing defects, cleaning, and clearing obstructions.
3. Fixing insulation boards to the walls, followed by a protective layer and decorative finish.

Where is external wall insulation used?

EWI is most suitable for homes with solid walls, including:

• Properties built before 1930 with solid brick walls.
• Concrete system-built homes from the 1930s–1980s.
• Properties with timber or steel frameworks.

Houses with cavity walls usually don’t require EWI, as insulation can be injected into the existing cavity instead.

Advantages of external insulation

• Lower energy bills: Reduces heat loss and energy use.
• Enhanced property value: Improves both energy performance and appearance.
• Comfortable temperatures: Keeps your home warmer in winter and cooler in summer.
• Smaller carbon footprint: Cuts household emissions by reducing reliance on heating and cooling systems.
• Quick installation: Carried out externally, causing minimal disruption indoors.

Costs and maintenance

The cost of external wall insulation varies depending on materials, property size, and complexity of installation. On average, homeowners can expect to pay between £8,000 and £22,000.

While upfront costs can be high, long-term energy savings can offset much of the expense. Maintenance is minimal, usually just occasional cleaning and inspections.

Things to be aware of

• Planning permission: May be required for listed buildings, conservation areas, or distinctive properties.
• Appearance changes: The exterior look of your home will be altered, though finishes can usually be customised.
• Space adjustments: Wall thickness increases slightly, which may affect external features like pipes or window sills.

Don’t Forget

External wall insulation can play a vital role in reducing energy bills and tackling fuel poverty, especially for vulnerable households.

Support has been available through government-backed schemes such as ECO4 or the Great British Insulation Scheme (GBIS). GBIS closed on 31 March 2026 and ECO4 ends on 31 December 2026.

See the home energy grants you can still get.