External Wall Insulation

What is external wall insulation?

External wall insulation, also known as EWI and external solid wall insulation, is a type of insulation that is attached to the outside of your walls. Two layers of material are used – one to offer insulation, and an outer layer of mineral or synthetic render to protect against weather and provide a decorative finish.

Installing EWI will add around 100mm to your house, depending on the thickness of insulation used.

External wall insulation

What buildings can external wall insulation be used on?

EWI is suitable for any building with solid walls. These can be:

  • Older properties built before 1930 that have solid brick walls
  • System built (concrete) properties that tend to have been built between the 1930s and 1980s
  • Solid wall properties with timber or steel frames

Houses built with cavity walls do not need EWI because they already have a space within the walls into which insulation can be injected. Many properties with cavity walls have already been insulated apart from what are known as “hard to treat” cavity walls that require more specialist treatment.

How do I tell if I have solid walls?

If your walls are brick, then the best way to tell if they are solid walls or cavity walls is to look at the brick pattern on the outside of the house.

If the bricks are all rectangular and laid end-to-end then the wall is probably cavity. If some of the bricks are laid with the square end facing out, then it is probably a solid wall.

If the brick work is covered up (eg with a pebble dash render) then it can be harder to identify.

Properties of a non-traditional construction, such as system built or timber framed houses, are likely to have solid walls.

If you have an Energy Performance Certificate (EPC) for your home, then you will be able to see what type of construction the walls are. This is typically listed on the second page of the document.

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