With rising energy prices and the cost of living crisis, we are all looking for ways to save on our bills at home. One of the best ways to make the most out of your heating system is to make sure you have adequate insulation.

You should insulate your loft or roof, and if you have cavity walls, then you will need to make sure you have cavity wall insulation, but what about adding insulation to exterior walls?

External wall insulation

Adding insulation to exterior walls is known as external wall insulation (EWI). It is a process by which layers of insulation are added to the exterior of the property and then covered with a render that both protects the system and gives the property an attractive finish.

How is external wall insulation different to other types of insulation?

There are three main types of insulation for walls:

  • Cavity wall insulation can only be installed in cavity walls, where holes are drilled in the exterior wall and insulation, such as mineral wool or polystyrene beads, is injected and then sealed with cement. 
  • External wall insulation can still be installed on cavity walls, but the cavity should be insulated first. 
  • Internal wall insulation adds insulation to the interior of the property, either by fixing rigid insulation boards to the walls or by building a stud wall filled with insulating material such as mineral wool fibre and affixing this to the existing wall.

How is external wall insulation fitted?

Adding insulation to external walls is a multi-step process that requires careful and experienced workmanship.

The first stage of adding insulation to external walls is to remove all fixings that protrude from the surface, such as lights and aerials. Then, a starter rail is fixed to the bottom of the wall to support the insulation, as well as sill boards to the bottoms of the windows. A 60mm thick insulation board is then fixed to the entirety of the exterior walls. 

The next stage involves applying a polymer-based render designed to adhere to the insulation board, followed by a glass fibre mesh set into the surface to provide additional strength, and then a thinner layer of render to cover it. 

Finally, a top coat is rendered onto the system, available in a choice of colours and finishes and containing marble dust to increase the durability of the surface.

Can you add insulation to exterior walls yourself?

External wall insulation should only be carried out by experienced and qualified professionals. Even if it were possible to obtain all of the correct materials at a reasonable price, the proper application of the layers is only possible through training and experience.

What are the benefits of adding insulation to exterior walls?

External wall insulation makes your home more thermally efficient – more so than cavity or internal wall insulation. EWI can reduce your annual heating bill by up to 50%. 

Additionally, EWI helps to prevent condensation from forming in the home and helps to reduce noise pollution. The rendered finish also gives you a chance to redecorate the outside of your home without any extra cost.


Adding insulation to exterior walls should be left to the professionals, but it is definitely a worthwhile investment, especially with the rising energy costs we are all currently dealing with.

If you are looking for professional external wall insulation installers, you can get in touch with us.