Is external wall insulation a good option for my home?

Insulating your home’s exterior could save you up to £260 per year* in energy bills – discover if it’s right for your project with Oliver’s advice

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Most of us live in ‘leaky’ homes that were built years ago when energy efficiency wasn’t a key consideration in construction, so insulating your property is key to improving comfort and achieving lower bills. We need to take action to prevent heat energy escaping, and the first step is to stop draughts. Once you’ve done this, insulation methods, such as external wall, cavity wall and loft, are the next step to keep your home warmer, more energy efficient and cheaper to run.

How it works

External wall insulation involves fixing an insulating material to the exterior façade of a building, creating an additional barrier between the outside and inside, which improves its thermal efficiency. Homes built before 1919 will most likely have solid walls, which let through twice as much heat as cavity walls, so insulating from the outside is a good option.

If you’re building a new structure, such as an extension, it will have to adhere to current building regulations, which stipulate the level of insulation. While a more expensive option compared to other types, external wall insulation has the capacity to significantly improve the U-value of your walls, making them more energy efficient and thus reducing heat loss.

The benefits

External wall insulation will drastically improve the thermal efficiency of your home, especially if you live in a semi-detached or detached property. The installation process will not affect the interior of the house and the panels will also improve the property’s weather and sound resistance, while renewing the outer appearance and protecting the brickwork underneath. The finish can be smooth, textured, painted, tiled, panelled or finished with brick slips to suit your home.

Insulating has significant benefits to your comfort levels and health, too. It’s not only about the payback period and money saved on bills, it is also about creating a home that will maintain good health by keeping you warm and reducing the potentially harmful effects of black spore mould caused by damp. When I renovated my own home, I found that any areas suffering with mould were cured once insulation and ventilation were installed.

Planning permission

Bear in mind that external insulation will change the appearance of your home, so in most cases this will mean planning consent will be required. If you live in a listed building or within a Conservation Area, your property may be subject to strict planning rules regarding the exterior, so it is best to check with your local authority or online at, as external insulation may not be a viable option.

Another point to consider is that, because the insulation panels will change the façade of your home, other external features, such as window frames and sills, gutters and downpipes, will be affected, as well as the junction between the walls and roof. Guttering and rainwater goods will have to be removed and refitted to the new render once it’s completed, and may need to be extended to compensate for the larger distance between walls and roof.

Also consider your home’s access, as the panels will add width to the walls, possibly narrowing side returns or alleys. Access will also be required during installation, so ensure there is enough room for professionals to work in.


Unlike cavity wall insulation – which involves inserting fibrous material through mortar holes into the gap inside the wall leaves – external insulation comes in panels of between 50mm and 100mm thick, and is applied on top of the outside brickwork. This effectively creates a new exterior wall, which will then be rendered. By using external insulation, you can choose to create a thicker layer of insulation of around 100mm, while most wall cavities measure about 50mm in width.

Before investing in external wall insulation, be aware that the installation process is much lengthier than that for cavity wall insulation, which can be completed in a few hours. It will take several days to do the main work, and then extra time should be factored in for adjusting sills and guttering.

It costs more than cavity wall insulation, too, with installation costing between £5,000 and £18,000, depending on your house type and size, according to the Energy Saving Trust, compared to £300 to £800 for cavity wall insulation.


Modern insulation materials are usually non-permeable and will be rendered or clad to prevent rainwater penetration; however, moisture build-up inside a house is a potential problem when insulating. Sufficient background ventilation will rectify this – speak to a surveyor or specialist company.

*according to the Energy Saving Trust, based on solid wall insulation on a semi-detached house