What is External Wall Insulation?

External wall insulation (EWI) is a method of improving a building’s thermal efficiency by adding a layer of insulating material to the exterior walls. This process involves fixing an insulating layer, such as expanded polystyrene, mineral wool, or polyurethane foam, to the outside of the existing walls. The insulation is then covered with a protective, weather-resistant finish, which can be render, brick slips, or cladding.

Overall, external wall insulation is a comprehensive solution for improving the thermal performance and aesthetic appeal of a building while providing long-term energy savings and environmental benefits.

What are the key benefits of EWI?

Enhanced Energy Efficiency

By reducing heat loss through the walls, EWI helps to lower energy consumption and heating costs.

Improved Comfort

Buildings with EWI maintain a more consistent internal temperature, making them more comfortable to live or work in.

Reduced Carbon Footprint

Lower energy use translates to reduced greenhouse gas emissions.

Increased Property Value

Improved energy efficiency and aesthetics can boost the market value of a property.

What is an EWI system made up of?

Decorative Finish

Render Primer

Fibreglass Mesh

Basecoat

EPS Insulation

Mechanical Fixings

Starter Track & Clip-on Profile

Adhesive

Substrate Preparation

EPS INSULATION SYSTEM onto Brickexpanded polystyrene

This highly popular system comprises EPS insulation on a brick substrate; the system is cost-effective, easy to install, and suitable for various properties. EPS adhesives and plastic pin fixings achieve an advanced insulation system with minimised thermal bridging and a prolonged lifespan. Decorative thin coat renders are available to seal the system and achieve an aesthetically pleasing finish. When installed on a solid brick wall, 90mm of EPS can achieve a U-value of 0.30(W/m2k). This aligns the building fabric with modern efficiency standards, effectively reducing energy bills and improving the thermal comfort of the property. The system creates a more comfortable internal environment and significantly updates the exterior look of the building, creating a fresh, modern finish.

How much does EWI cost?

The cost of external wall insulation (EWI) can vary significantly based on factors such as the size and type of the property, the materials used, and the complexity of the installation. Here are some rough average costings for different types of households in the UK:

Detached

Average Cost: £15,000 – £20,000

Detached houses generally have more external wall area to cover, leading to higher costs. The range depends on the size of the house and the insulation material chosen.

Semi-Detached

Average Cost: £8,000 – £10,000

Semi-detached houses share one wall with another property, reducing the amount of external wall that needs insulation compared to detached houses.

Bungalow

Average Cost: £6,000 – £8,000

Bungalows, being single-storey buildings, have a larger footprint relative to their height, resulting in significant external wall area but generally less than multi-storey houses.

Mid-Terrace

Average Cost: £5,000 – £7,000

Mid-terrace houses share two walls with neighbouring properties, significantly reducing the external wall area that needs insulation, resulting in lower costs.

End-Terrace

Average Cost: £6,000 – £8,000

End-terrace houses have one wall exposed in addition to the front and back walls, leading to slightly higher costs than mid-terrace houses but lower than semi-detached houses.

Flats (per unit)

Average Cost: £3,000 – £6,000

The cost for flats can vary widely depending on whether the whole block is being insulated or just individual units. The cost tends to be lower per unit due to shared walls and the potential for cost-sharing among residents.

Material Choice

Different insulation materials (e.g. expanded polystyrene, mineral wool, phenolic foam) have varying costs.

Finish

The choice of render, cladding, or brick slips can also affect the final cost.

Labour and Location

Labour costs can vary depending on the region and the complexity of the installation.

Key Factors Influencing Costs

What are the average annual savings and payback times homeowners can expect from installing EWI?

The average household energy bill in the UK can be broken down into several key components. As of the latest figures from Ofgem, the typical annual dual fuel (electricity and gas) energy bill is approximately £1,277. According to the Energy Saving Trust, heating accounts for about 55-60% of the average household’s energy consumption. Using the average annual energy bill of £1,277, we can estimate the proportion spent on heating. The total heating costs range from £702.35 (55% of £1,277) to £766.20 (60% of £1,277).

Average bills change depending on wholesale energy prices, network costs, operating costs, and other factors. Your energy bills may be higher than the average, depending on how much energy you use in your home. British Gas publishes updates on average bill prices periodically, with the latest set of figures available for access on https://www.britishgas.co.uk/energy/guides/average-bill.html.

Based on this data, we can estimate the annual savings and payback time for external wall insulation (EWI), helping households make informed decisions about energy efficiency investments.

House Type	Average Cost Of EWI	Average Annual Savings	Average Payback Time	Average Payback Time using GBIS funding
Detached	£15,000 – £20,000	£800 – £1000	20 Years	10-12 Years
Semi-detached	£8,000 – £10,000	£500 – £700	15 Years	7-8 Years
Bungalow	£6,000 – £8,000	£500 – £700	12-15 Years	6-8 Years
Mid-terrace	£5,000 – £7,000	£400 – £600	11-13 Years	5-7 Years
End-terrace	£6,000 – £8,000	£500 – £700	12-15 Years	6-8 Years
Flat (per unit)	£3,000 – £6,000	£200 – £400	12-14 Years	6-7 Years

Explore Case Studies On External Wall Insulation

View case studies