External Wall Insulation

In building, EWI stands for External Wall Insulation. It is a method of improving a property's thermal efficiency by fixing a layer of insulation material directly to the outside of the building's walls, which is then covered with a protective and decorative render or cladding.

An insulated render system is a multi-layered approach to thermal insulation applied to the exterior of a building. These systems help improve thermal efficiency and enhance energy performance while protecting the building façade. It typically involves the following layers:

  • Rigid Insulation: This layer consists of boards or sheets that provide thermal insulation.
  • Reinforcing Mesh: Applied over the insulation, this mesh enhances structural integrity.
  • Render Base Coat: A layer of base coat material is applied to the mesh.
  • Finishing Coat: The final layer is a protective render finish.

  

 

Insulated render systems are commonly used for improving thermal efficiency and enhancing energy performance in buildings.

  • Insulation: The core component of an insulated render system is the insulation material. Common options include:
    • Expanded Polystyrene (EPS): Lightweight and easy to install, EPS slabs are mechanically fixed to the existing wall.
    • Mineral Wool Slab: Provides good thermal performance and fire resistance.
    • Phenolic Foam Slab: Offers excellent insulation properties.
  • Mechanical Fixings: These are used to attach the insulation boards to the wall. They can be made of metal or plastic. To minimize thermal bridging, adhesive-fixed insulation or a track & rail system can be used.
  • Mesh Reinforcement: A mesh is applied over the insulation to create a key backing for subsequent layers.
  • Render Base Coat: This layer provides a smooth surface for the final finish. It’s typically applied over the mesh.
  • Finish Coat: The outermost layer is the decorative render finish.
    • Silicone Render: Durable and water-repellent.
    • Mineral Render: Breathable and natural-looking.
    • Polymer Plain Render: Versatile and available in various colors.
    • Polymer Dashing Render: Textured finish with added aggregates.
    • Rendabrick: Simulates brickwork appearance.
    • Acrylic and Silicate Renders: Different finishes for aesthetic variety.

The execution of separate insulated render systems:

 

  • EPS (Expanded Polystyrene) System:
  • Prepare the Surface: Clean and repair the existing wall surface.
  • Fix Insulation Boards: Mechanically fix EPS insulation boards to the wall using appropriate fixings (screws or nails).
  • Apply Base Coat: Apply a base coat (usually cement-based) over the insulation boards.
  • Install Reinforcement Mesh: Embed a fibreglass mesh into the base coat while it’s still wet.
  • Apply Finish Coat: Once the base coat is dry, apply the final decorative render finish (e.g., silicone render, acrylic render).
  • Mineral Wool System:
  • Surface Preparation: Clean and repair the wall.
  • Attach Insulation Slabs: Fix mineral wool slabs to the wall using adhesive or mechanical fixings.
  • Base Coat Application: Apply a base coat (cementitious or polymer-based) over the insulation.
  • Mesh Reinforcement: Embed a mesh into the base coat.
  • Final Render Coat: Apply the chosen render finish (e.g., mineral render, acrylic render).
  • Phenolic Foam System:
  • Surface Preparation: As with other systems, prepare the wall.
  • Fix Phenolic Foam Slabs: Attach phenolic foam slabs using mechanical fixings.
  • Base Coat and Mesh: Apply a base coat and embed reinforcement mesh.
  • Finish Coat: Apply the desired render finish.

The finish coat in an insulated render system is the outermost layer that provides both aesthetic appeal and protection.

  • Types of Finish Coats:
  • Silicone Render: Durable, water-repellent, and available in various colors.
  • Mineral Render: Breathable and natural-looking.
  • Acrylic Render: Versatile and easy to apply.
  • Polymer Plain Render: Offers different finishes for aesthetic variety.
  • Polymer Dashing Render: Textured finish with added aggregates.
  • Rendabrick: Simulates brickwork appearance.
  • Application Process:
  • After applying the base coat (which provides a smooth surface), the finish coat is applied.
  • It can be trowel-applied or sprayed onto the surface.
  • The thickness of the finish coat varies based on the system and manufacturer’s recommendations.
  • Benefits:
  • Weather Resistance: Finish coats protect against rain, UV exposure, and temperature fluctuations.
  • Decorative: They enhance the appearance of the building.
  • Breathability: Some finishes allow moisture vapour to escape while maintaining water resistance.