External wall insulation (EWI) is a method of improving the thermal performance of a building by adding insulation to the outside of its external walls. Rather than installing insulation inside the property, an EWI system is built on the external wall and finished with a protective render or other suitable finish.
For properties where improving wall insulation is part of a wider renovation project, external wall insulation can be an important part of the overall approach. It combines insulation materials, fixings, basecoat, reinforcement mesh, primer, and a suitable external finish to create a complete system.
How Does External Wall Insulation Work?
An external wall insulation system adds a layer of insulation to the outside of the existing wall. The insulation helps reduce heat transfer through the wall, while the outer layers protect the system and provide the finished appearance.
A typical EWI build-up can include:
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Insulation boards – These form the main insulating layer and can include EPS insulation boards.
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Insulation adhesive – Used where appropriate to help secure the insulation boards to the wall.
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Insulation fixings – Mechanical fixings or insulation anchors can provide additional support.
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Reinforcing mesh – Embedded within the basecoat to reinforce the rendered layer.
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Render basecoat – Provides the base layer over the insulation and reinforcement.
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Primer – Used where required as part of the chosen render system.
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External render – The final finish can provide the desired appearance and help protect the underlying system.
The exact materials and installation method depend on the EWI system and the requirements of the building.
What Materials Are Used for External Wall Insulation?
Different materials can be used within an EWI system. EPS insulation is one example and is available in different board types and thicknesses.
Other important components include insulation fixings, fibreglass or reinforcing mesh, adhesives, and render products.
Choosing compatible components is important because an EWI system is made up of several layers that work together. The insulation, basecoat, reinforcement, and final render should therefore be considered as part of the overall system rather than as completely separate products.
What Are External Wall Insulation Boards?
External wall insulation boards are installed over the existing external wall to create the insulating layer.
EPS insulation boards are commonly associated with EWI applications and are available in different specifications. The appropriate board depends on the requirements of the project and the system being used.
It is also important to consider the supporting products required to complete the installation, including suitable insulation adhesive, fixings and reinforcement mesh.
Why Is Reinforcing Mesh Used?
Reinforcing mesh is incorporated into the basecoat layer of an EWI system. Fibreglass and other reinforcing meshes are designed to reinforce the render build-up.
The mesh sits within the basecoat rather than simply being placed underneath the finished render. This creates a reinforced layer between the insulation and the final finish.
The correct mesh should be selected according to the requirements of the particular system.
What Is the Role of External Render?
External render forms the visible outer finish of many EWI systems. It can change the appearance of the building while providing a protective finish over the underlying layers.
There are different render options available, including silicone render, acrylic render, mineral render, and coloured render. The appropriate choice depends on the system, substrate, desired finish, and project requirements.
For example, silicone render is one of the important product categories within the wider render market, while coloured render can provide a finished appearance without relying solely on a separate decorative coating.
External Wall Insulation vs Internal Wall Insulation
The main difference is where the insulation is installed.
External wall insulation is installed on the outside of the building. It forms an external system consisting of insulation, reinforcement, and a suitable finish.
Internal wall insulation is installed on the inside of the building and therefore involves a different installation approach.
The right option depends on the property, existing wall construction, available space and the requirements of the project. External wall insulation may be particularly relevant where external renovation and a new façade finish are being considered together.
What Should You Consider Before Choosing EWI Materials?
Before selecting materials, it is important to consider the complete system rather than choosing individual products in isolation.
Consider:
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The type and specification of insulation boards
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The required insulation thickness
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Compatible adhesive and fixings
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The appropriate reinforcement mesh
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Basecoat requirements
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Primer requirements
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The final render finish
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Compatibility between the different components
For larger projects, selecting products from a suitable EWI system can help ensure that the different layers are designed to work together.
Is External Wall Insulation Suitable for Every Property?
There is no single EWI solution that is suitable for every building. The existing wall construction, condition of the substrate, insulation requirements, detailing, and desired external finish all need to be considered.
Where a complete external wall insulation system is being planned, professional assessment, and appropriate installation guidance should be followed.
Find External Wall Insulation Materials
Infinity PM supplies products across the EWI and external render categories, including insulation boards, insulation fixings, reinforcing mesh, basecoat materials, and render products.
If you are planning an external wall insulation project, exploring the different EWI materials and external wall insulation boards, Infinity PM can help you understand the components required for the system.
Frequently Asked Questions
What Is External Wall Insulation?
External wall insulation is a method of insulating a building by installing insulation to the outside of its external walls, followed by reinforcing and finishing layers.
How Does an EWI System Work?
An EWI system adds an insulation layer to the external wall and uses components such as fixings, basecoat, reinforcing mesh, primer, and external render to create the finished system.
What Are EWI Insulation Boards?
EWI insulation boards are insulation products designed for use as part of an external wall insulation build-up. EPS insulation boards are one type used in EWI applications.
What Is Reinforcing Mesh Used for in EWI?
Reinforcing mesh is incorporated into the basecoat layer to reinforce the render build-up over the insulation.
Can External Wall Insulation Be Finished with Render?
Yes. Render is commonly used as the external finish of an EWI build-up, with options including silicone, acrylic, mineral, and coloured renders depending on the system and project requirements.