External Wall Insulation – Benefits, Costs, Systems and Process

External wall insulation (EWI) involves fixing insulation boards to the exterior walls of a building, then covering them with decorative render or cladding. This can significantly improve thermal efficiency in buildings with solid masonry walls.

Benefits of External Wall Insulation

• Creates a warmer home by preventing heat loss through walls
• Can reduce heating bills by up to 35%
• Prevents condensation and mould growth on walls
• Weatherproofs exterior walls and enhances durability
• Improves soundproofing and noise insulation
• Minimal loss of internal floor area compared to internal insulation
• Extends the lifespan of walls by protecting from weather damage
• Enhances external appearance of property through new render or cladding

How EWI Systems Work

There are a few key components in a typical external wall insulation system:

• Insulation boards – Rigid boards made of mineral wool, EPS, XPS or phenolic foam. They come in various thicknesses.
• Mechanical fixings – Special plastic or metal fixings that secure boards to the wall surface.
• Basecoat and reinforcing mesh – Fibreglass mesh embedded in a basecoat render to form the base layer.
• Primer – Helps topcoat render adhere properly.
• Topcoat render – The final decorative and weatherproof finish, available in various textures and colours.
• Beads – Edge profiles to provide neat trim finishes around windows, doors and corners.

Assessing Wall Suitability

EWI can be applied to most structural wall types, but a survey should check for:

• Damp or salt issues that need remediating first.
• Wall condition – surfaces should be sound to fix boards securely.
• Areas of potential risk like parapets or overhangs.
• Guttering and drainage systems – may need adjusting.
• Existing fixtures – assess treatment around windows, pipes, etc.

Installation Process

Installation typically follows these steps:

1. Prepare wall surface – repairs, cleaning etc.
2. Apply base rails and corner beads.
3. Fix insulation boards with adhesive and mechanical fixings.
4. Apply basecoat render with reinforcing mesh.
5. Apply primer.
6. Apply final decorative render or cladding finish.
7. Make good details around windows, doors, pipes etc.

The process takes around 2-4 weeks depending on building size and labour crew size. Access scaffolding is erected to reach higher areas. Residents may need to vacate if external access is blocked.

Costs and Considerations

• EWI costs around £100-£150 per m2 installed, although larger projects can benefit from economies of scale.
• Planning permission may be required – check with your local authority.
• Building regulations approval is needed, including for fire safety.
• Scaffolding adds significantly to costs but is essential for safe installation.
• Disruption is moderate during installation due to external works.
• A reputable installer should provide guarantees for materials and workmanship.
• Can qualify for ECO funding if solid walls lack insulation.

Overall, EWI requires a serious investment, but delivers excellent thermal performance that can pay back in energy savings over time. It is one of the most effective ways to insulate challenging solid wall properties.