In an era of rising energy costs and growing environmental concerns, homeowners and builders are increasingly turning to External Wall Insulation (EWI) as a means to improve energy efficiency and reduce carbon emissions. 

EWI involves adding an insulating layer to the exterior walls of a building, improving the property’s ability to maintain its internal temperature. This means keeping warm air inside the building in winter, and cool air inside the building in summer.  

However, as it the case with most kinds of property alteration, it also comes with its own set of drawbacks. In this article, we will explore the advantages and disadvantages of EWI to help homeowners make informed decisions about their energy-saving options.

External Wall Insulation
External Wall Insulation (EWI) being installed in the rear of a property in Brighton.

Benefits of External Wall Insulation:

1. Enhanced energy efficiency:

 One of the primary benefits of EWI is its ability to significantly improve a building’s energy efficiency. External walls are the largest area of heat loss in a typical domestic property. 

By creating a thermal barrier on the exterior walls, it reduces heat loss and minimises thermal bridging. It wraps the external wall envelope in an insulating layer, helping to eliminate thermal bridges at corners. This leads to a more consistent and comfortable indoor temperature, reducing the need to use energy for heating and cooling.

Consequently, homeowners can enjoy lower energy bills and reduced reliance on fossil fuels.

2. Increased comfort:

EWI improves thermal comfort within a building by reducing heat loss. It helps maintain a consistent temperature throughout the house, reducing cold surfaces and the likelihood of warm moist air condensing on these cold surfaces, the main cause of internal damp and mould. Damp and mould growth can negatively impact indoor air quality and occupants’ health.

3. Improved weatherproofing, maintenance & external appearance:

Another advantage of EWI is its ability to protect the external layer of the wall underneath from wind-driven rain and weathering generally. This means it is also a useful addition to cavity walls in areas where there is an increased risk of exposure to weathering and where cavity wall insulation (CWI) would be a damp risk if installed on its own. It can also transform the appearance of a building. 

The insulating layer can be finished with various materials, such as render, brick slips, or cladding, providing a fresh and updated look. This allows homeowners to enhance the visual appeal of their property while simultaneously improving its energy efficiency and durability.

4. Minimal disruption & enhanced soundproofing:

EWI is applied from the outside, so does not disrupt the day-to-day activities of occupants inside. EWI not only reduces heat loss but also acts as an effective sound barrier. It can significantly reduce noise pollution from outside sources, such as traffic or neighbours, creating a quieter and more peaceful indoor environment. This is particularly beneficial for properties located near busy roads or in densely populated areas.

Drawbacks of External Wall Insulation:

1. High initial cost:

One of the main drawbacks of EWI is the initial investment required. The process involves significant labour and material costs, including the removal of existing finishes and services such as guttering. As well as repairing any general defects, eg. cracks, causes of damp ingress, and preparing the external wall surface, other alterations may be required.

 Window sill extensions and sometimes roof extensions are also required to cover the EWI thickness if there is not enough roof overhang. Once the wall is prepared, the insulation boards or thermal plaster, followed by the external finishes can be applied.

However, it is important to note that the long-term energy savings and Government incentives like the Great British Insulation Scheme (formerly: Energy Company Obligation Plus or ECO+) may help offset the initial expense.

2. Impact on external features & aesthetics:

Installing EWI can alter the appearance and architectural features of a building. The thickness of the insulation layer may change window and door reveals, and the addition of cladding or render can modify the building’s original character. This becomes more of an issue in a Conservation Area (CA), or if the building has heritage status.

Careful consideration should be given to the design and selection of materials to ensure a cohesive and visually appealing result. Older properties are generally designed to be ‘moisture-open’ i.e. they need to breathe, so natural, breathable insulation materials need to be applied to control moisture and allow it to evaporate throughout the seasonal variations of the year.

3. Planning and building regulations:

EWI projects may require planning permission and compliance with local building regulations, whether in CAs or not. This is especially the case with a Heritage/ Listed building and requires careful preservation of its historic features and aesthetic qualities in relation to its surroundings.

 Homeowners should consult with local authorities and professionals to understand the necessary approvals and ensure compliance with relevant guidelines. Failure to adhere to regulations can lead to costly delays and potential legal issues.

4. Maintenance and repair challenges:

External Wall Insulation systems require periodic maintenance to ensure their long-term effectiveness. The external finishes may deteriorate over time, necessitating repairs or replacement, but no more than standard wall exteriors. 

Additionally, accessing the underlying wall for any maintenance or repairs can be more challenging compared to traditional wall systems if, for example, water ingress occurs internally through breaches in the wall or somehow gets behind the insulating layer externally. 

However, this should not happen if regular maintenance is adhered to as with any standard uninsulated property. Because the exterior of the wall is protected by the EWI, it is less likely to need the same levels of maintenance.


External Wall Insulation offers significant benefits, including improved energy efficiency, enhanced comfort, soundproofing, and aesthetic improvements. However, it is crucial to consider the drawbacks, such as the initial cost, potential impact on external features, compliance with planning & highways regulations, and ongoing maintenance requirements.

Homeowners should carefully evaluate their specific needs, budget, and preferences before deciding whether EWI is the right choice for their property.

Engaging the services of a professional energy consultancy and conducting a cost-benefit analysis will help ensure a well-informed decision that maximises energy savings and comfort while minimising any potential drawbacks.

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