What is external wall insulation?

Installing external wall insulation is like putting a winter coat on your home. A layer of insulation material is applied to the outer walls. This layer is then covered 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.

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 typically cost £12,000 to insulate.
  • Can cause issues with damp if installed incorrectly.
  • May require planning permission.
  • Scaffolding will need to be put up at your property during 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. This means the outside walls are made from a single layer of solid stone or brick. Unlike with cavity walls, there is no gap between the outside wall and the inside wall.

There are two ways to insulate a solid wall. Insulation can be added to the outside of the property (external wall insulation) or it can be added to the inside of the property (internal wall insulation).

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

You should speak to different installers to get an idea of which type of insulation would be best suited to your property.

Is external insulation right for my home?

It’s important take a ‘whole house approach’ when working out if external wall insulation is right for your home. This means looking into how external wall insulation will affect different aspects of the building, especially how air and moisture circulate.

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

Layers of external wall insulation

External wall insulation is applied in different layers. It’s a little like layering up a sandwich, where the bottom slice of bread is your exterior wall.
There are three different parts involved in the layering of external wall insulation. Each part has different options, with variations in both cost and performance.

External wall insulation boards

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 external wall insulation boards are applied directly to the exterior wall.

External wall insulation fixings

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

External wall insulation finishes

External wall insulation finishes are the final layer of external wall insulation. They provide protection for the insulation beneath, additional weatherproofing for your home, and an aesthetically pleasing finish to the wall.

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. A sand and cement mix are applied over a wire mesh. Alternatively, lime-based render may be used instead of sand and cement. Wet render can also be pebble-dashed over, creating an attractive finish.

Dry cladding involves adding boards, panels or tiles as the final layer of 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. 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 are available to help with the cost of installation. See the section below for more details.

External wall insulation grants

Home Energy Scotland are offering £7,500 of grant funding for homeowners in Scotland looking to install external wall insulation. An extra £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 to reduce the cost. If other work needs doing on the outside of your home, getting external wall insulation at the same time could help make a saving.

External Wall Insulation FAQ

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

Scaffolding will be required. If you have a garden, items like furniture will need to be moved out of the way.

The time it takes can vary significantly. Private installs may be as quick as two weeks. Installs through a funded project will likely take considerably longer.

The weather and temperature can also affect the time the install takes.

Depending on the type of render you choose, there may be extra disruption. If stone chips are used, these will end up on the ground/in the garden during the rendering stage (when the final layer is added to the wall).

The installer should clean these up at the end of the install. They should also take 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. 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 to have the work carried out.

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: National Insulation Association