External Wall Insulation

External wall insulation or solid wall insulation involves insulating a building by attaching a layer of insulation material to the external wall and covering it with reinforcement and finally rendering it.

Often referred to as cladding the process is great to save on heating bills but can also be protective and decorative.


What is External Wall Insulation?

There are three types of insulation that can be used for external wall insulation. These are:

  • Expanded Polystyrene
  • Mineral Wool
  • Phenolic Resin

The most popular of these is the expanded polystyrene, used as it is the most cost-effective way of carrying out the work. The others are used in more specific circumstances and you should ask your installer if you want to know more about them.

External Wall Insulation

How Does it Work?

Like cavity wall insulation, external wall insulation works by creating a barrier that prevents the heat from transferring through your walls and instead bouncing this back in. This slows the movement of heat out through the walls, reducing your heating demand dramatically, lowering your heating bills and energy output.

The most commonly used insulation expanded polystyrene slabs contain thousands of trapped air pockets that make it an extremely good insulator. This further helps to stop the heat from escaping to the outside.

How external wall insulation works

Installation Process

Before installing, our surveyor will visit the premises to ensure that external wall insulation is the right solution for your property.

Once this has been carried out, there are a few additional preparation bits that need to be implemented before starting. Firstly, if there is some existing render this needs to be tested to ensure it is strong enough to hold the new insulation. If not, this will need to be removed.

Secondly, all the pipework will need removing from the building, this will be reinstalled once the insulation had been attached.

Once the walls have been prepped the installers will take out the following steps.

  1. Insulating Panels fixed to the wall, with plastic capped fittings to tie panels securely to the wall
  2. Mortar is applied to cover the insulating panels and fittings
  3. An insulating mesh is then added to the wall and sunken within the mortar applied previously
  4. The render finish (available in any colour) is applied on top of the freshly sanded and painted mortar

External wall insulation being installed

The finish available can vary. Naturally the most cost-effective is with a simple white render, but other colours are available. You can also choose a finish that is:

  • Smooth
  • Textured
  • Painted
  • Tiled
  • Panelled
  • Pebble-dashed


Before and after external wall insulation has been installed

For more information on the finishes available please speak with your installer.


Can I Benefit from External Wall Insulation?

Almost anyone can benefit from external wall insulation provided they have a solid wall. The benefits of reduced heating bills and energy expenditure are much greater than they are for other forms of insulation such as cavity wall and loft insulation, but it is also more expensive.

External wall insulation can also improve the value of the house. The EPC rating of a house has been known to jump 2 bands. This will depend on your home but it is almost certain to add value to your home as well as improving the look and feel for passersby.

In addition to improving the comfort of your home external wall insulation can:

  • Renew the appearance of outer walls. Coloured finishes can be applied to save redecoration costs in the future
  • Improve weatherproofing and sound resistance
  • Fill cracks and gaps in the brickwork, which will reduce draughts
  • Increase the life of your walls by protecting the brickwork
  • Reduce condensation on internal walls and can help prevent damp (but will not solve rising or penetration damp)


How do I know if I have solid walls?

Brick Patterns


If your home was built before the 1920’s the external walls are probably solid and do not have a cavity. One way to tell is to measure the width of the wall by looking at an external wall window or door. If the brick wall is less than 260 mm then it is likely a solid wall.

Another way to tell is by looking at the pattern of the bricks. If you see a full brick followed by a half brick continuously (like the image on the right) then it is likely a solid wall. If it’s all full bricks this is likely a cavity wall.

The Benefits of External Wall Insulation

Will it cost me?

The average cost of external wall insulation is much greater than cavity wall insulation and will depend on the size of the property and if it’s detached, semi-detached, terrace, bungalow or flat.

Installation cost for external wall insulation can be between £9,000 to £26,000 and between £4,000 to £16,000 for internal wall insulation when unsubsidised.

New government criteria offers funding for those on benefits to insulate their homes however currently there is no funding for those for solid wall insulation.

We offer both finance and one time payment options.

How much will I Save?

External wall insulation saves more in energy bills and energy expenditure than any other form of insulation we offer. The cost is offset by the saving with a semi-detached medium size house saving an average of £270 per year.


The Impact on the environment

As much as 1,900kg of carbon dioxide can be saved by implementing external wall insulation for a detached house. Even for a flat, this can save as much as 600kg of carbon dioxide, making the potential benefit for the environment huge.

Frequently Asked Questions

Below is a list of frequently asked questions relating to external wall insulation.

Does external wall insulation have any downsides?

External wall insulation is not as straightforward as other forms and may need additional organisation and work:

  • You may have to apply for planning permission and scaffolding will be needed whilst the external walls are being fitted. Because of the insulation adding onto the external walls of your property any satellite dishes and pipes etc. on the outside of your property will have to be replaced.
  • Windowsills and roofs may possibly have to be extended if you’re fitting external wall insulation if they aren’t already wide enough.

Does external wall insulation cause mould?

External wall insulation will not cause mould and should, in fact, help prevent it. By using a qualified installer, they will take measure to ensure the home can breathe correctly, and that previous ventilation isn’t covered.

Does external wall insulation create a fire hazard?

If the correct British Board Agreement (BBA) materials are used, then external wall insulation poses no fire threat.

Can external wall insulation be bad for your health?

No, correctly fitted external wall or solid wall insulation do not contain loose fibres and instead come in solid blocks and are then sealed with impermeable render coats, meaning that there is no way for them to be damaging to health.

Does external insulation make algae more likely?

The right products will never promote algae growth due to the biocides used within the render.

Is external wall insulation ugly?

Although it is a matter of opinion, external wall insulation could often be considered to make a home better looking as it covers up the underlying wall and is then painted, this removes the visibility of any old marks or old looking paint from the previous walls.

How long does external wall insulation last?

when installed correctly most system manufacturers give a minimum warranty of 25 years although you can expect the systems to last much longer providing it is properly encased in a waterproof render coating protecting it from the weather.

Do you have to get planning permission for external wall insulation?

Although in most cases planning permission isn’t needed for domestic properties certain areas or buildings can require planning permission, it is best to check with your council before you begin.

Will external wall insulation improve my home value?

External wall insulation can both make your home look much better as well as increasing the EPC rating which will directly improve the property value.

How long does external wall insulation take to install?

External wall insulation typically takes between 2-3 weeks to fit but will vary depending on size.

Can I still live at home whilst external wall insulation is being installed?

Yes, the fitting of external wall insulation shouldn’t affect your normal living life at home except from there being scaffolding around your house.