When looking at ways to insulate a building, two options commonly considered are external wall insulation (EWI) and internal wall insulation (IWI). Both approaches add insulation to the building, but they differ significantly in where the insulation is installed and how the work affects the property.
Understanding the difference between external and internal wall insulation can help homeowners, landlords and building professionals decide which approach is more appropriate for a particular project.
What Is External Wall Insulation?
External wall insulation involves installing an insulation layer to the outside of the building's existing walls.
The insulation is normally fixed to the external wall and then covered with a reinforced layer and an external finish, such as render.
A typical EWI build-up can include:
- Insulation boards
- Insulation adhesive
- Mechanical insulation fixings
- Reinforcing mesh
- Basecoat
- Profiles and beads
- Primer
- External render
The exact materials and system construction depend on the selected EWI system and building requirements.
What Is Internal Wall Insulation?
Internal wall insulation is installed on the inside face of an external wall.
Instead of changing the outside of the property, insulation is added internally to the wall surface. The construction method and materials can vary depending on the building and the internal wall being treated.
Internal insulation can therefore be considered where external insulation is unsuitable or where retaining the existing external appearance is an important consideration.
External vs Internal Wall Insulation
The main difference is the location of the insulation.
External wall insulation:
- Installed on the outside of the wall
- Can form part of an external render system
- Changes the external wall finish
- Does not require insulation to be fitted directly onto the internal room surface
Internal wall insulation:
- Installed on the inside of the external wall
- Changes the internal wall build-up
- Can affect available internal space
- Does not normally require the external façade to be covered with an insulation system
Both approaches need to be considered in relation to the building and the intended insulation specification.
External Wall Insulation: What Are the Advantages?
One of the main characteristics of EWI is that the insulation is installed externally.
This can make it an option for projects where the external façade can be altered as part of the work.
EWI can also be combined with an external render finish, giving the building an opportunity for an updated external appearance.
Other considerations include:
- No direct loss of room floor area from installing insulation internally
- Insulation is positioned continuously across the external wall where the system allows
- External render can form part of the finished system
- Suitable for projects already requiring external wall or façade work
The suitability of EWI depends on the individual property and system specification.
Internal Wall Insulation: What Are the Advantages?
Internal wall insulation can be useful where work to the external façade is not practical or desirable.
Because the insulation is installed inside, the outside appearance of the building can remain unchanged.
It may therefore be considered for properties where external alterations present particular challenges.
However, internal insulation can reduce the available internal space and may require changes to the room's wall finish.
Which Is More Suitable for an Older Property?
Older buildings can require particularly careful consideration when choosing between external and internal insulation.
Factors such as the existing wall construction, external appearance, available space and condition of the building can all influence the decision.
For some properties, EWI may provide an opportunity to insulate the outside of the wall while also renewing the external finish. In other situations, internal insulation may be the more practical approach.
The correct option should be determined from the requirements of the individual building rather than simply choosing one method for every property.
External Wall Insulation and Render
A major part of many EWI projects is the external finishing system.
Once the insulation boards are installed and the reinforced layer has been prepared, a suitable primer and external render can be applied.
Depending on the system, materials can include:
- EPS insulation boards
- Insulation fixings
- Reinforcing mesh
- Basecoat
- Render primer
- Silicone render
- Coloured render
This makes EWI particularly relevant to projects where insulation and external façade improvement are being considered together.
What Should You Consider Before Choosing?
Before deciding between external and internal wall insulation, consider the complete project.
1. Building Construction
The existing wall type and construction can affect the available insulation options.
2. External Appearance
If maintaining the existing external appearance is important, internal insulation may need to be considered.
3. Internal Space
Internal insulation can alter the internal wall build-up and may reduce usable room space.
4. External Space and Boundaries
External insulation adds to the outside face of the wall, so the available space around the building may need to be considered.
5. Render and Finish
If the project includes an external render upgrade, EWI may be considered alongside the external finishing work.
6. Complete System Requirements
Insulation boards, fixings, adhesive, mesh, basecoat, primer and render need to be selected according to the intended system.
External Wall Insulation Materials
If you are considering EWI, selecting the correct materials is an important part of the project.
Common external wall insulation materials include:
- EPS insulation boards
- Insulation fixings
- Insulation adhesive
- Fibreglass reinforcing mesh
- Base tracks
- Corner beads
- Basecoat
- Render primer
- External render
Infinity PM supplies a range of these products for trade and building projects.
External Wall Insulation from Infinity PM
Infinity PM provides EWI materials and external wall insulation products for UK trade customers.
The range includes categories covering:
- External Wall Insulation
- EWI Materials
- EWI Systems
- EWI Insulation Boards
- EPS Insulation Boards
- Insulation Fixings
- Insulation Mesh
- External Wall Render
- Silicone Render
- Render Systems
Customers can explore the available products and select materials according to their individual project and system requirements.
Final Thoughts
The choice between external wall insulation and internal wall insulation depends on the building, available space, desired finish and requirements of the insulation project.
External wall insulation places the insulation outside the building and can be combined with a new external render finish. Internal wall insulation is installed inside and can be useful where changing the external façade is not suitable.
Neither approach is automatically right for every property. The building construction and complete project requirements should be considered before selecting an insulation method.
FAQs
What is the difference between external and internal wall insulation?
External wall insulation is installed on the outside of the building, while internal wall insulation is installed on the inside face of the external wall.
Is external wall insulation better than internal wall insulation?
There is no single option that is best for every property. The appropriate method depends on the building, available space, external appearance and project requirements.
Does external wall insulation change the appearance of a building?
It can. EWI is installed externally and is commonly finished with render or another suitable external finish.
Does internal wall insulation take up room space?
It can, because the insulation is installed on the internal side of the wall and changes the internal wall build-up.
Can EPS boards be used for external wall insulation?
Suitable EPS insulation boards can form part of an EWI system. The board should be selected according to the requirements of the particular system and project.
What materials are needed for external wall insulation?
Depending on the system, materials can include insulation boards, adhesive, mechanical fixings, reinforcing mesh, basecoat, profiles, primer and external render.