Your External Wall Insulation in detail - Greenhus

Your External Wall Insulation in detail

What will I have on my walls?

In all cases, Greenhus aims to improve the thermal performance of your walls to the equivalent of a new-build, i.e. with a u-value of 0.3 W/m2K. (See our section on heat loss for a simple understanding of u-values). We achieve this thanks to the heart of the system – the insulation board.

This is either Expanded Polystyrene (EPS) or Mineral Wool. With most wall constructions, we will need to use a 90mm thick EPS insulation board or a 120mm thick mineral wool board to achieve the desired thermal performance. (Mineral Wool does not have such good insulating properties, so a greater thickness is required to achieve the same thermal improvement.)

How long will it last?

Greenhus uses only BBA-accredited systems, which are required to demonstrate a 25-year life expectancy. (The earliest example of External Wall Insulation that still performs as installed dates back to 1957, so you can be confident of at least 25 years.) As the system uses inert products that won’t interact with the environment, there is no reason why your installation should not give decades of trouble-free benefits.

How thick will my system be?

To achieve our target thermal improvement and reduce your wall u-value to 0.3 W/m2K, Greenhus will typically apply 90mm of EPS or 120mm of Mineral Wool. In each case, the associated layers will add further thickness. With EPS, there will an additional 12mm (approx.) and for Mineral Wool there will be an additional 15mm (approx.).

The rule is:

EPS total thickness = Insulation board + 12mm (so 102mm/4” in most applications)

Mineral Wool total thickness = insulation board + 15mm (so 135mm/5.5” in most applications)

How will this affect my window sills and other fixtures?

At Greenhus, we take a “whole property” approach and will amend all your external features to accommodate the increased wall thickness. This will involve extended window sills and the extension/re-routing of wall-mounted pipework.

How is it installed?

You can find a full step-by-step description here,  including actual photographs of Greenhus installations.

System detail – What is EPS?


EPS foam is a rigid, tough, close-cell foam. It is made using solid beads of polystyrene which are then expanded during production to form perfectly-closed cells. The production process increases the volume of the cells by up to 50 times. Once cooled, the foam can be cut or shaped depending on its intended use, in our case for External Wall Insulation boards.

It’s important that the boards are dimensionally stable for use in EWI – we don’t want movement. To achieve this, the manufacturing process includes processes to age and cure the boards.

When used for External Wall Insulation, boards can be supplied in thicknesses of between 20mm and 380mm. The thicker the board, the greater the insulating qualities. We will recommend the necessary thickness as part of our free quotation service.

  • Close-cell foam insulation board
  • Lightweight
  • Inert and non-toxic
  • Does not contain Chlorofluorocarbons (CFCs) or Hydrofluorocarbons (HCFCs)
  • 100% recyclable
  • Global Warming Potential < 5
  • Thermal conductivity (K-value) of 0.030 W/mK (use this value as a comparison with other insulation products)

System detail -What is mineral wool?

Mineral wool is extremely popular for thermal insulation. Typically, rock, silica or ceramic is heated until molten then spun into threads. These threads are then treated with resin-binder and water-repellent mineral oil. Finally, they are woven into a mat. The thickness of the mat is pre-determined by the intended use.


When the individual threads are woven to create the actual insulation boards, they trap air. Air is a very good insulator, which means the insulation boards enjoy very good insulation properties.

When used in External Wall Insulation, the boards will be supplied in thicknesses of 40mm – 300mm. The thicker the board, the greater the insulating qualities. We will recommend the necessary thickness as part of our free quotation service.

  • Spun-thread insulation board
  • Good fire-protection and acoustic properties
  • Environmentally-friendly – production uses 30-60% material recycled from slag, a waste product from blast furnaces
  • Global Warming Potential < 5
  • Thermal conductivity (K-value) of 0.036 – 0.04 W/mK (use this value as a comparison with other insulation products)

What is the build-up of External Wall Insulation?

Here, you can see where the insulation sits within the build-up. Simply click on the other products for a full description, or read below.

Adhesive. Applied to the back of the boards with a 10mm notched trowel. The 10mm adhesive ridges will compress as the board is pushed against the wall, creating a regular 5mm thick bond, as shown here.

Meshcoat. 2 render layers are applied, with a fibreglass mesh inserted, as shown here.

Primer. A primer is painted on, which contains quartz particles to provide a “key” for the final render.

Textured render. The final stage in your installation is the application of a 100% waterproof, through-colour textured render. With a silicone content to ensure weatherproofing, and flexible enough to withstand knock and bumps, this render is maintenance-free.

Because it’s a “through-colour” coating, it can be pressure-washed should it need cleaning – the colour cannot be removed.

Plus, it will never need re-painting, saving you thousands on materials, labour and scaffold. (If you do decide to change the colour of your property in years to come, it can be painted using appropriate paints – simply speak to us and we’ll supply the right products.)

To see how the addition of External Wall Insulation by Greenhus can make your home warmer and give it a complete makeover that will last many years, please complete our Contact Form.

Don’t forget our FAQ section!

Discover how External Wall Insulation from Greenhus can transform your home or business premises - complete our Contact Form and we’ll call you back, or speak to us on 01822 819 911

To find out how Greenhus can help you plan a great improvement to your home or business,
complete our Contact Form or call us on 01822 819 911