Energy Efficiency Measure Guide: External Wall Insulation (EWI)

Note: All installations must comply with current regulations, which are subject to change.

Key Points to Consider

• Someone must be present during installation – either you or someone you trust.
• Several stages of installation are weather-dependent and may be delayed.
• Your local planning department may require a red brick render finish to match surrounding properties.
• Ventilation upgrades will likely be required.
• Scaffolding will be erected for installation.

See our ventilation/scaffolding guide for more details.

What is External Wall Insulation?

External Wall Insulation (EWI) adds a thermal layer to the outside walls of a building.

Nearly half the heat lost from solid wall houses (without a cavity) escapes through the walls. EWI helps retain heat, making homes warmer and more energy-efficient.

The process involves:

• Adding insulation to external walls.
• Coating with protective render or cladding.
• Planning Permission:

Required if EWI changes the property's appearance or if walls abut a public highway (including pavements).

YES will arrange this – do not start an application yourself.

Common Misconceptions

“EWI causes damp and mould”

Properly installed EWI prevents damp by:

• Raising wall surface temperature.
• Reducing condensation.
• Blocking external moisture.
• Damp usually results from poor installation or pre-existing issues.

“EWI is only for older homes”

• EWI benefits both old and new buildings by improving thermal comfort and energy efficiency.

“EWI makes homes too airtight”

If installed without proper ventilation, this can be true.

• EWI systems are designed to work with ventilation upgrades to ensure fresh air circulation.

“EWI negatively impacts indoor air quality”

EWI improves air quality by:

• Controlling moisture.
• Reducing mould growth.
• Working with ventilation systems.

“EWI only helps in winter”

• EWI also keeps homes cooler in summer by reducing heat transfer.

“EWI is difficult to maintain”

• EWI systems are durable and require minimal maintenance.

The Installation Process

Presence Required:

You or someone you trust must be present during installation. Installers will advise on daily schedules.

Before Installation

A survey will assess:

• Access restrictions, boundary walls, lean-to structures.
• Clearance for scaffolding.
• Roof line extension needs.
• Windowsill extension needs.
• Exterior fittings (guttering, pipes, lights, satellite dishes).
• Ventilation sufficiency.
• Planning permission requirements.
• Red brick finish requirements (if applicable).
• Party wall agreement needs (for shared walls or extensions).

During installation

EWI installation involves 5 stages:

Scaffolding & Skip Delivery (up to 3 days)

• Delays may occur due to access issues or severe weather.

Enabling Works (up to 5 days)

• Includes ventilation upgrades, roof line extensions, etc.

EWI Installation (up to 14 working days)

• Insulation Fixing (~2 days)
• Base Coat Application (~5 days)
• Topcoat/Render Application (~7 days)

Property Protection

• Temporary downpipes installed if originals are removed.
• Openings sealed to prevent water ingress.
• Exterior Fittings
• Extended or adjusted as needed.

Finish options:

• Red brick (if required by planning).
• Standard white or cream render.

After installation

Scaffolding remains for a few weeks for post-installation access.

Maintenance recommendations

• You’ll receive a maintenance guide tailored to your installed products. General advice includes:
• Keep gutters and pipes clear.
• Periodically inspect for cracks or damage.

Handover documents

Upon completion and sign-off, you’ll receive:

• Trustmark Certificate
• Insurance-backed guarantees
• Building regulations certificate (or competent persons scheme evidence)
• Claim of compliance document
• Workmanship guarantee
• Manufacturer’s warranty
• EWI Maintenance Guidance