What is external wall insulation?
External wall insulation (EWI)is a layer of insulating material that is added to the outside of a building in order to improve energy efficiency .
EWI is often used for buildings which have solid walls and insufficient space within the property to add internal insulation.
External wall insulation is one of the most effective methods of improving the thermal efficiency of a property, delivering a significant upgrade to the Energy Performance Certificate (EPC) and increasing property value
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Benefits of external wall insulation:
Enhanced energy efficiency
The primary benefit of external wall insulation is the significant difference it will make to a building’s thermal heat retention. External walls are the largest area of heat loss in a typical domestic property (35%), so addressing this should be a key concern for any homeowner.
By creating a thermal barrier on the exterior walls, EWI reduces heat loss and minimises thermal bridging. It wraps the external wall envelope with an insulating layer, helping to eliminate thermal bridges at corners. This reduces the amount of heat required to achieve a comfortable temperature, resulting in cheaper energy bills for homeowners.
Better comfort and health outcomes
Exterior wall insulation improves the thermal comfort of a building by reducing heat loss through walls.
This 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 be detrimental to indoor air quality and your health.
Improved weatherproofing, maintenance & external appearance
Another advantage of outside wall insulation is its ability to protect the wall underneath from wind and rain. This means it can be a useful addition to cavity wall insulation in areas where there is an increased risk of exposure to weathering or where cavity wall insulation (CWI) could become damp.
External house insulation can also transform the appearance of a building for the better. 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.
Enhanced soundproofing
EWI insulation 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
Cost of external wall insulation
External wall insulation costs tend to be high, as the process involves significant labour and material costs, including the removal of existing finishes and fixings such as guttering. The cost of installing external wall insulation can depend on the size of the surface area to be covered, the depth of the insulation, and the type of insulating material to be installed (foam, fiberglass, mineral wool, and cork are all possible options).
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.
The long-term energy savings achieved from installing EWI, combined with Government incentives like the Great British Insulation Scheme (formerly: Energy Company Obligation Plus or ECO+) may help offset the initial expense.
Impact on insulation on external walls
External wall insulation finishes 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 or if the building has heritage status.
Careful consideration should be given to the design and selection of external cladding 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.
Planning permission for external insulation
EWI projects may require planning permission and compliance with local building regulations, whether in conservation areas 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 speak with local authorities and a retrofit assessor to understand the necessary approvals and ensure compliance with regulations. Failure to adhere to planning permissions can lead to costly delays and potential legal issues.
Maintenance and repair challenges
External wall insulation systems require occasional maintenance to ensure their long-term effectiveness. The external finishes may deteriorate over time, requiring repair or replacement, but no more than standard wall exteriors would.
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 kept up, 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.
Is external wall insulation worth it?
External wall insulation offers property owners significant benefits, including improved energy efficiency, enhanced comfort, better soundproofing, and visual appeal.
However, it is crucial to consider some of the potential , such as the initial cost, potential downsides of external wall insulation, which may include challenging compliance with planning & highways regulations, ongoing maintenance requirements. and the initial cost of external wall insulation.
Homeowners should carefully evaluate their specific needs, budget, and preferences, before deciding whether external wall insulation is worth it.
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.
If you would to speak with a BHESCo Retrofit Assessor about the suitability of external wall insulation for your property, and whether it will be a worthwhile investment that will save you money in the long-term, then please leave your details using the contact form below.
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