Understanding the Key Differences Between Internal and External Wall Insulation

Keeping a home warm during colder months can be a challenge, especially when heating costs rise and energy efficiency becomes a priority. One of the most effective ways to create a warmer home and reduce energy bills is through wall insulation. But when it comes to insulating your walls, should you choose internal wall insulation or external wall insulation? Both methods improve comfort and reduce heating needs, but they work in different ways and suit different types of homes.

This post breaks down the key differences between internal and external wall insulation to help you decide which option fits your needs best.

External wall insulation being applied to a house exterior

What Is Internal Wall Insulation?

Internal wall insulation involves fixing insulation materials to the inside of your external walls. This method is often used in homes where external changes are restricted, such as listed buildings or houses in conservation areas.

How It Works

• Insulation boards or insulated plasterboard are attached directly to the inside walls.

• The walls are then finished with plaster or drywall.

• This creates a thermal barrier that reduces heat loss through the walls.

  
  

Advantages of Internal Wall Insulation

• Cost-effective: Generally cheaper to install than external wall insulation.

• Less disruption outside: No changes to the building’s exterior appearance.

• Suitable for certain homes: Ideal for properties where external work is not allowed.

  
  

Disadvantages to Consider

• Reduced room size: Adding insulation inside can slightly reduce the internal space.

• Potential for cold bridging: If not installed correctly, heat can escape through gaps.

• Disruption inside the home: Installation requires moving furniture and some redecorating.

  
  

What Is External Wall Insulation?

External wall insulation involves fixing insulation material to the outside of your walls, then covering it with a protective render or cladding.

How It Works

• Insulation boards are attached to the external walls.

• A weatherproof finish is applied over the insulation.

• This method wraps the building in a thermal layer, reducing heat loss significantly.

  
  

Advantages of External Wall Insulation

• Improves building appearance: Can refresh the look of your home with new render or cladding.

• No loss of internal space: Keeps your rooms at their full size.

• Better thermal performance: Covers the entire wall, reducing cold spots and drafts.

• Protects walls: Shields the building structure from weather damage.

  
  

Disadvantages to Consider

• Higher upfront cost: More expensive than internal insulation due to materials and labor.

• Planning permission may be needed: Especially in conservation areas or for listed buildings.

• Disruption outside: Scaffolding and external work can affect your garden or driveway.

  
  

Internal wall insulation being installed on an interior wall

How Both Types of Insulation Help Reduce Energy Bills

Both internal and external wall insulation work by reducing heat loss through walls, which is a major source of wasted energy in many homes. By keeping heat inside, your heating system doesn’t have to work as hard, leading to:

• Lower energy consumption

• Reduced heating bills

• A warmer home during cold months

  
  

For example, a typical uninsulated solid wall can lose up to 35% of heat through its surface. Adding insulation can cut this loss by up to 70%, depending on the material and installation quality.

Choosing the Right Insulation for Your Home

When deciding between internal and external wall insulation, consider these factors:

• Building type and age: Older homes with solid walls often benefit more from external insulation.

• Planning restrictions: If you live in a protected area, internal insulation might be your only option.

• Budget: Internal insulation usually costs less upfront but may require more maintenance.

• Space considerations: If you want to keep your room size, external insulation is better.

• Aesthetic preferences: External insulation can improve or change your home’s look.

  
  

Practical Tips for Installation

• Hire a professional surveyor to assess your home’s walls and recommend the best insulation type.

• Check for any damp or structural issues before installation, as these need fixing first.

• Consider combining wall insulation with loft or floor insulation for maximum energy savings.

• Look for insulation materials with good thermal performance and fire safety ratings.

• Plan for some disruption during installation, especially with internal wall insulation.

  
  

Final Thoughts on Wall Insulation Choices

Choosing between internal and external wall insulation depends on your home’s characteristics, budget, and personal preferences. Both options can significantly reduce heating costs and create a warmer home, helping you avoid the discomfort of a cold home during winter.