External Wall Insulation

Heat escapes from your home in multiple places – notably your walls. Luckily, by insulating your home's walls you can reduce heat loss, save money on your energy bills, and significantly reduce your carbon footprint.

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There are a few ways you can insulate your home’s walls and it mainly depends on the type of walls your home has. External insulation is one of the most common types of insulation for older properties, typically ones built before the 1920s that aren’t suitable for cavity wall insulation.

Find out more about external wall insulation, the advantages and disadvantages, and how much you can expect to pay.

external wall insulation

Do I Need External Wall Insulation?

The first thing to establish is whether external wall insulation is suitable for your property, or whether you’ll have to consider installing another type of insulation. To do this, let’s dive into the difference between cavity walls and solid walls and the options with insulating them.

A cavity wall is a wall with a cavity (hollow space) in the middle of it. These types of walls actually comprise two parts, and these parts are connected to make one wall. Cavity walls were introduced in the 1920s to help with ventilation, so if your house was built in the last 100 years, you’ll likely have these types of walls.

A solid wall doesn’t have a cavity inside it; it’s simply one solid wall. Houses built before the 1920s tend to have solid walls. If you’re not sure whether your walls are cavity walls or solid walls, you can check the brickwork. If the brick wall is even and all the bricks are a similar length, you likely have cavity walls. If you’re unsure either way, call in a professional who can give you more information.

If you have solid walls, there’s no way to fill a cavity with insulation, so cavity wall insulation is not an option, and you’ll instead have to insulate either the outside or internal walls. We’ll be exploring the former option – external insulation.

If you want to improve your home’s thermal efficiency, external solid wall insulation is an excellent option. You can expect significant reductions in your energy bills and a smaller carbon footprint.

What is External Insulation?

External insulation involves fixing a layer of insulation to an existing wall. You’ll finish the layer either with a type of cladding or a coat of render to protect it from weather and water. External wall insulation is a common form of insulation for homes that have solid walls.

External vs Internal Insulation

With solid wall properties, there’s no option to install insulation into interior cavities, since no cavities exist. Instead, you have to add insulation either to the inside or the outside of the walls – known as internal or external insulation. 

Internal wall insulation:

  • Tends to be cheaper than external insulation
  • Is more disruptive to install
  • Requires skirting boards, door frames, etc, to be detached
  • Reduces the amount of floor space you have in your home.


External wall insulation: 

  • Can be applied to your property without significant disruption
  • Renews the appearance of outer walls and helps to reduce damage from the elements
  • Soundproofs your home
  • Can increase the lifespan of your walls by protecting the brickwork
  • Fills cracks and gaps in the brickwork, which reduces draughts. 


When it comes to external insulation, a considerable advantage is that you don’t have to take up space inside your home. Internal wall insulation, on the other hand, reduces the space in your home’s interior. You’ll pay significantly more for the benefits associated with external wall insulation or solid wall insulation systems, though, so consider your budget before committing. 

Pros & Cons of External Wall Insulation

Like every insulation material, there are advantages and disadvantages to installing external wall insulation. Let’s explore some of the main ones. 


External wall insulation cost can be high, but you certainly get a lot for your investment in terms of long-term benefits. According to the Energy Saving Trust, you can expect to save anywhere from £240 per year to a whopping £930, depending, of course, on the size of your property just by having external wall insulation installed. Over a lifetime, your insulation will not only pay for itself, but save you money, too.
By insulating the route through which draughts tend to enter, you can keep your home warmer in the colder months.
One of the most obvious advantages that external wall insulation has over the internal insulation alternative is that it doesn’t reduce your internal floor space. Instead, you build outwards onto the front of your property.
Noisy neighbours, street noise, and traffic can all negatively impact your quality of life. Luckily, external wall insulation is famous for improving your home’s soundproofing – a happy side effect of having a more thermally efficient home.


External wall insulation isn’t a straightforward job; it requires installation by an experienced professional and, in many cases, planning permission from your local authority. This also means that the council has a right to refuse to give planning permission, which could put a spanner in the works of your project.

External wall insulation is one of the most efficient types of insulation, simply because of how much heat is lost through our walls. This efficiency, however, does come with a higher price tag, so external wall insulation might not be suitable if you’re working to a tight budget.
While installing external wall insulation doesn’t usually directly cause damp and condensation, it does happen occasionally. The good news is that with a trusted provider, you should be able to establish before fitting insulation whether it’s likely to cause an issue for your property.

Types of External Wall Insulation

This type of insulation comprises polystyrene balls packed tightly together to make a board. EPS is cheap, light, and easy to work with. The trapped air bubbles in the material prevent heat from transferring from one side of the board to the other. 

One of the main disadvantages of this material is its poor fire rating.  When the EPS is integrated into a fully covered system, this shouldn’t matter too much, as the fire should come into contact with the render before making it into the insulation. It’s worth considering, though, if fire safety is a key concern.

Mineral wool is also a common material in loft insulation systems. When used for external walls, the mineral wool is further compressed into a rigid board. The benefit of this type of insulation is that, unlike EPS, it has a high fire resistance rating. It’s great for soundproofing, too. On the other hand, the heaviness of the material makes it more difficult to work with, which can increase labour costs. 

Wood fibre is the most sustainable option for your home as it can be made from recycled materials, typically from the sawmill industry. This material tends to come in boards or quilts and also offers excellent thermal efficiency. The biggest disadvantage of wood fibre is its high cost compared to other external wall insulation materials. 

Can I Install External Wall Insulation Myself?

While it’s tempting to try your hand at an external wall insulation DIY project, this type of insulation isn’t suitable for installation by anybody other than a professional, unless you have previous experience with projects just like this one.

Instead, search online for a qualified professional installer with previous experience and the reviews to show for it.

External Wall Insulation and Damp

Whichever type of insulation you opt for – whether it’s internal, external, in your walls or your loft – you shouldn’t go ahead if damp and condensation are present in the area.

There’s a complicated relationship between external wall insulation and damp that should be considered before going ahead with insulation. Before cavity walls were introduced, solid brick walls tended to be impermeable walls that stops moisture penetration.
Many insulation materials are non-permeable and clad to prevent rainwater penetration.

They can’t, however, prevent moisture from the inside of the home from reaching the wall, so more ventilation is needed to remove moisture from the air before it reaches the walls.

The air’s dew point is the point at which air meets a temperature that causes the moisture to condense into water. The temperature through a wall changes as the air moves from the external temperature to the internal temperature.

If the wall doesn’t have a ventilated cavity, the dew point should occur on the external surface. Adding insulation, however, can change the dew point of the air that enters through your wall.

External insulation heats your wall, which moves the dew point towards the cooler, external air, reducing the risk of condensation. Unfortunately, in some cases, the dew point occurs between the insulation and the wall or in the insulation itself, causing condensation.

When left unchecked, condensation can lead to long-term issues such as damp and mould. To avoid this happening, install a vapour barrier between the wall and the insulation. Ask your supplier for more information.

Do I Need Planning Permission to Install External Wall Insulation?

No matter how you install external wall insulation, the simple fact is it will change the external appearance of your property. In many cases, that change requires planning permission from your local authority.

This is especially important if your property is a listed building or within a conservation area, and in this case, your local council might refuse to give consent.

How to Reduce the Costs of External Wall Insulation

There are no two ways about it; external insulation isn’t cheap. If you’re working to a tight budget, however, and want to save some money, here are some tips. 

  • Fit external insulation while you’re having other work done to the outside, such as solar panels or a new roof. This will mean you’ll already have scaffolding up, which can save on the costs. 
  • Ask for quotes from reputable suppliers. We can help you with this by introducing you to trusted installers for a highly competitive quote.
  • There’s financial support available for certain people who want to install insulation. See if you’re eligible by checking government grants.


If external wall insulation isn’t financially feasible for you, but you want the benefits that come with installing insulation, try a different type, such as loft insulation. Loft insulation tends to be cheaper and will also help to keep your home cooler in the same, warmer in the winter, and more environmentally friendly all year round.

Is Installing Solid Wall Insulation Worth It?

If you have solid walls in your home and you’re looking for a way to save costs and the planet at the same time, external wall insulation offers an excellent solution. There are, however, some things to consider before you go ahead.

If you work with the right professional, they’ll be able to let you know whether your home is suitable for external wall insulation and whether it’s likely to cause any problems with damp, for example. 

Remember to ask whether you need planning permission from your local authority before starting a project. Failing to do so can have costly consequences, especially if you live in a listed property.

If you’ve decided to go ahead with wall insulation, we can help by introducing you to trusted installers who can advise you on the best wall insulation option for your home and then provide you with a highly competitive quote. By using our recommended insulation installers will provide you with full peace of mind that the insulation job you have done will be completed to the highest standards, providing you with energy bill savings for many years to come.

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