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Outside Wall Insulation: The Smart Way to Insulate

Outside wall insulation which is more commonly known as External Wall Insulation (EWI), is one of the most effective ways to improve your home’s energy performance, cut heating bills, and enhance the visual appearance of your property. With UK energy costs staying high and more households aiming for better EPC ratings, EWI has become a leading home upgrade solution for solid wall homes.

We at ECO Insulation explain how outside wall insulation works, costs, benefits, materials, drawbacks, DIY considerations, and more.

What Happens When You Externally Insulate Solid Walls?

Solid wall homes (typically built before the 1930s) lose heat rapidly because they have no cavity to trap warmth. When you install external wall insulation,

1. A Continuous Thermal Barrier Is Created

Insulation boards are fixed to the outside of your home, stopping heat escaping through the solid walls. This can reduce heat loss by up to 60%.

2. The Internal Space Is Left Undisturbed

Unlike internal wall insulation, EWI does not reduce your room sizes or require major indoor disruption.

3. The Home Becomes More Comfortable

You’ll typically notice:

  • Warmer rooms in winter

  • Fewer cold spots and draughts

  • Better temperature stability

4. Your Exterior Receives a Fresh New Finish

A reinforced render system or decorative cladding is applied over the insulation, transforming the look of your home and improving kerb appeal.

5. The Walls Gain Added Weather Protection

EWI adds a protective shell that shields your property from:

  • Driving rain

  • Frost damage

  • Cracking and moisture penetration

This can increase the lifespan of older brick or stone homes.

Deciding Between Internal and External Wall Insulation

If your home has solid walls, you generally have two options. An internal wall insulation (IWI) or an external wall insulation (EWI).

Here’s how they compare:

External Wall Insulation (EWI) – Advantages

  • No loss of interior space

  • Minimal indoor disruption

  • Improves exterior appearance

  • Helps eliminate damp penetration

  • Provides excellent thermal performance

  • Suitable for most solid-wall homes

Internal Wall Insulation (IWI) – Advantages

  • Lower upfront cost

  • Ideal for flats where external work is restricted

  • Useful if you plan to renovate individual rooms

When to choose internal insulation

  • If the building is listed

  • If it’s in a conservation area

  • If boundary constraints prevent external work

When to choose external insulation

  • For whole-house insulation

  • If you also want to modernise the exterior

  • When reducing moisture penetration is a priority

  • If indoor disruption must be avoided

In most UK solid wall homes, external wall insulation offers the best overall performance and long-term value. It is also more common.

What Is the Best Insulation for Outside Walls?

The ideal insulation material depends on your property type, budget, and performance needs. The most commonly used EWI materials in the UK include:

1. Expanded Polystyrene (EPS)

  • Most affordable

  • Lightweight and highly efficient

  • Popular for general domestic installations

2. Mineral Wool

  • Excellent fire resistance

  • Highly breathable (great for older, moisture-prone walls)

  • Ideal for traditional or heritage properties

3. Phenolic Foam

  • Highest thermal performance per thickness

  • Perfect for areas where space is limited or maximum performance is needed

4. Wood Fibre Boards

  • Natural, breathable and eco-friendly

  • Helps manage moisture in older stone and brick homes

  • Often used in conservation and retrofit projects

Most UK homeowners choose EPS or Mineral Wool, but your installer will recommend the best system after surveying your home.

What Are the Downsides of External Wall Insulation?

External wall insulation offers major benefits, but it’s important to be aware of potential drawbacks:

1. Higher Upfront Cost

EWI is more expensive than internal wall insulation due to:

  • Scaffolding

  • Specialist materials

  • Labour-intensive installation

2. Planning Restrictions

Listed buildings and some conservation areas may require permission—or may not allow external insulation at all.

3. Temporary Disruption to the Outside of Your Home

Expect scaffolding and external works for 2–4 weeks depending on property size.

4. Poor Installation Can Lead to Issues

If not installed correctly, EWI can cause:

  • Trapped moisture

  • Cracking or render failure

  • Cold bridging

Using a qualified, accredited installer is essential.

5. Appearance Will Change

While many homeowners welcome a refreshed exterior, those wanting to keep original brickwork exposed may prefer internal insulation.

Can I Install Exterior Wall Insulation Myself?

Technically, you could attempt a DIY installationm but it is not recommended for the following reasons, especially if you have no previous experience.

1. Specialist Skills Are Required

Correct installation involves:

  • Fixings

  • Adhesives

  • Mesh reinforcement

  • Render systems

  • Weatherproofing details

Improper installation can lead to serious structural and moisture problems.

2. Building Regulations Apply

EWI upgrades must comply with UK Building Regulations for:

  • U-values

  • Fire safety

  • Ventilation

  • Insulation continuity

DIY installs often fail inspections.

3. Manufacturer Warranties Won’t Apply

Most EWI systems require approved installers for warranty coverage.

4. Access Equipment Is Needed

Scaffolding, safety equipment, and professional tools add cost and risk.

In short: EWI is a professional job.Homeowners are strongly advised to use an accredited installer like those from ecoinsulation.co.uk to ensure long-term performance and compliance.

Is Outside Wall Insulation Worth It in the UK?

For most UK homes with solid walls, yes. Benefits include:

  • Major reduction in heat loss

  • Lower energy bills

  • Improved thermal comfort

  • Better EPC rating

  • Enhanced appearance

  • Reduced carbon footprint

With energy prices remaining high and more people aiming for greener homes, external wall insulation remains one of the best long-term home improvements available.

Get a Free Outside Wall Insulation Survey

ecoinsulation.co.uk provides:

  • Free home energy surveys

  • High-performance EWI systems

  • Accredited installers

  • Access to UK grants (ECO4, LA Flex & more)

  • Long-term warranties

  • Professional advice for solid-wall homes

Ready to upgrade your home?
Get a free no-obligation quote and start saving on your energy bills today.