External Wall Insulation

Installing external wall insulation is like putting a winter coat on your home. An installer applies a layer of insulation material to the outer walls, then covers this with render or cladding.

An installer in a high vis orange jacket and white hard hat on a scaffold. They are adding external wall insulation to a house.

What is External Wall Insulation (EWI)?

External Wall Insulation is one way to stop heat loss through a solid (non-cavity) wall. An installer applies a layer of insulation material to the outer walls, then covers this with render or cladding.

Adding this extra layer of insulation means that less warmth escapes through the walls. As well as keeping the heat inside your home, you’ll also be better protected against rain and bad weather.

What’s more, external wall insulation also has the added bonus of a fresh new look for your property. There are lots of different options when it comes to the type of finish you want.

Advantages of external wall insulation


  • Can save you money on your heating bills.
  • Refreshes your home’s appearance.
  • Reduces condensation on internal walls.
  • No changes or disruption to the inside of the house.
  • Better protection against wind and rain.

Disadvantages of external wall insulation


  • Relatively expensive. A typical three-bed semi-detached house will cost around £12,000 to insulate.
  • Can cause issues with damp if installed incorrectly.
  • May require planning permission.
  • Scaffolding is needed for installation.

External wall versus internal wall insulation

Both external and internal wall insulation are solutions for insulating a solid wall. Most homes built before the 1920s will have solid walls, i.e. the outside walls are a single layer of solid stone or brick. Unlike cavity walls, there is no gap between the outside wall and the inside wall.

There are two ways to insulate a solid wall. You either add insulation to the outside (external wall insulation) or the inside (internal wall insulation) of your home.

Whether you choose external or internal wall insulation will depend on a number of things, including:

  • Budget
  • Level of disruption
  • Condition of the walls
  • Planning permission

Speaking to different installers will help you choose the best insulation for your property.

Is external wall insulation right for my home?

It’s important take a ‘whole house approach’ to insulation. This means looking at how external wall insulation will affect different aspects of the building, especially how air and moisture circulate.

A good installer will help you decide on the best type of external wall insulation for your home. They will work out an option which keeps your home warm whilst avoiding problems with damp and condensation.

Layers of external wall insulation

Installers apply external wall insulation in layers. Basically, it’s similar to making a sandwich, where the bottom slice of bread is your exterior wall.

There are three different layers of external wall insulation. Each layer has different options, with variations in both cost and performance.

The external wall insulation boards make up the layer that actually keeps the heat in. They’re made from an insulating material such as mineral wool or expanded polystyrene. The installer applies external wall insulation boards directly to the exterior wall.

External wall insulation fixings keep the insulation securely in place. The insulation is fixed to the wall with a series of battens (frames), an adhesive, or a combination of the two.

External wall insulation finishes are the final layer of external wall insulation. They protect the insulation beneath and increase the weatherproofing of your home. Additionally, they give the wall an aesthetically pleasing finish.

There are two types of external wall insulation finishes: wet render and dry cladding.

Wet render is a lot like plastering over an internal wall. The installer applies a sand and cement mix over a wire mesh. Alternatively, they may use a lime-based render instead of sand and cement. You can pebble-dash over wet render to create an attractive finish.

Dry cladding involves adding a finishing layer of boards, panels or tiles to the external wall insulation. Dry cladding tends to be more expensive than wet rendering, but there are a wider range of materials and designs on offer.

External wall insulation cost

The cost of external wall insulation will depend on the size of your property. For example, a three-bed semi-detached house typically costs £12,000 to insulate.

To reduce the cost, many people decide to have external wall insulation carried out at the same time as other work to their property.

External wall insulation grants can help with the cost of installation. See the section below for more details.

External wall insulation grants

Home Energy Scotland offer £7,500 of grant funding for homeowners in Scotland looking to install external wall insulation. In addition, £2,500 is available as an interest-free loan.

To apply for an external wall insulation grant, call Home Energy Scotland’s freephone number on 0808 808 2282. One of the advisors will be able to take you through the process.

Grant funding may not fully cover external wall insulation, so it’s worth looking into additional ways of reducing the cost. Getting external wall insulation at the same time as other exterior work to your property could help you make a saving.

External Wall Insulation FAQs

Installers will only need access to the outside of your property – they shouldn’t need to come inside.

External wall insulation requires scaffolding. As a result, if you have a garden, you’ll need to move any obstacles (like furniture) out of the way.

The time it takes can vary significantly. On the one hand, private installs may be as quick as two weeks. On the other hand, installs through a funded project can take considerably longer. Furthermore, weather and temperature will affect the time the install takes.

Depending on the type of render you choose, there may be extra disruption. For example, stone chips often end up on the ground/in the garden during the rendering stage (when the installer adds the final layer to the wall).

The installer should clean these up at the end of the install, as well as taking measures to protect your doors and windows during the rendering stage.

Yes, in most cases. The best option is to have the whole block insulated, because this will give the block a consistent look.

Depending on your tenure (the type of ownership you have, or the type of lease you have) you may require permission for the work.

It may be possible to just insulate the wall outside your flat, but not all installers will offer this. If in doubt, it’s best to consult a few different installers.

A list of accredited installers can be found on the National Insulation Association’s website.

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Home Energy Scotland logo

Changeworks delivers Home Energy Scotland in the south east and Highlands and Islands on behalf of the Scottish Government and Energy Saving Trust.

As well as providing free, impartial expert advice to thousands of people every month to help them to keep warm in their homes for less, they identify funding opportunities for households seeking to install energy efficiency measures.

For more information, give Home Energy Scotland a call on 0808 808 2282 or email and the team will be happy to help you.