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How Much Does External Wall Insulation Cost

28 June 2024

External wall insulation (often abbreviated to EWI) is a brilliant way to supercharge your home's energy efficiency, dramatically reduce heating bills, and even enhance its kerb appeal. But before you embark on this journey towards a cosy interior and revamped exterior, there’s an important question to ask: how much will it cost? 

This MisterRender blog examines the factors that influence EWI costs, giving you a clear picture of what to expect.

So, let’s get down to business and discover all the facts you need to make an informed choice... 

An External Wall Insulation

What Is External Wall Insulation?

Before exploring the costs, it's vital to understand exactly what EWI is, as confusion abounds in this subject!

Essentially, it's a process where a layer of insulation material is added to the exterior walls of your house. This creates a thermal barrier that keeps heat in during winter and out during summer, making your home more energy-efficient.

Typically, there are three layers: the insulation board is fixed to the wall first, followed by a tough mesh sandwiched between thin layers of render (for strength). An outer coat of render or cladding completes the process.

While this doesn't seem difficult to grasp, consumers are often left baffled by contractors who use confusing or contradictory terms, or who offer to apply render only and refer to it as external wall insulation!

Discover more: What Is External Wall Insulation

the External Wall Insulation

What Is Solid Wall Insulation?

Basically, it's just another name for external wall insulation, although in this case it is applied to older properties that lack a cavity wall.

Before the 1930s, most houses had stone walls or solid brick walls, meaning that all the external walls were constructed of a single layer of brick or stone (although stone walls often had a double layer with rubble infill).

After this time, cavity walls were introduced. These comprised two layers of brick with a gap between them. Later examples started to use an outer wall of brick with an inner wall constructed using concrete blocks (or cinder blocks).

The air trapped between the two walls provided some insulation, although the main purpose was to allow moisture that made it through the first wall to drain away naturally without breaching the second wall.

This method, however, was not without its problems. For example, thermal bridging (or cold bridging) became an issue, where heat escapes during cold weather or enters during hot weather. This caused (and still causes!) problems with condensation forming on the inside walls*, leading to mould growth.

*This is caused by the difference in temperature between cold external air and warmer internal air.

The problem is that different materials conduct heat at different rates. Materials like metal are good conductors, while air and insulation are poor conductors. A thermal bridge happens when a highly conductive material creates a direct path through the building envelope, bypassing the insulation.

Poor workmanship didn't help, and this still continues to play a part in the ongoing issue of condensation and mould in houses today.

Still, cavity wall insulation has helped in many cases, although it still hasn't fixed the problem entirely...but that's a subject for another time!

Now let's get back to our main point, which is to answer the question; how much does external wall insulation cost?

Solid Wall Insulation

Is It Worth Installing External Wall Insulation?

To answer this, we need to evaluate all the facts, including potential costs, so let's see what we can discover.

First, the bad news: external solid wall insulation is comparatively more expensive than cavity wall insulation.

This is because the cavity wall insulation process is relatively easy, while an EWI project on solid walls is much more involved.

Explore in-depth: Does External Wall Insulation Add Value To Your Home

Worth Installing External Wall Insulation

Factors Affecting External Wall Insulation Cost

As you've probably already guessed, the overall cost of external wall insulation depends on a variety of factors, including the following:

Material Costs 

  • Type and thickness of insulation - Different insulation materials (e.g., mineral wool, expanded polystyrene boards, phenolic foam) have varying costs per square metre. Thicker insulation generally offers better thermal performance but comes at a higher price. 
  • Fixings and Adhesives - These are needed to secure the insulation boards to the existing wall. 
  • Render or Cladding - The final external finish is applied over the insulation. Options include silicone render, brick slips, wood fibre, or timber cladding. Each material has its own cost range. 
  • Scaffolding - Required to safely access the upper parts of the house during installation. 

Labour Costs 

  • Size and complexity of the house - Larger houses or those with intricate features (bay windows, extensions) require more time and labour for installation, increasing the cost. 
  • Installer experience and qualifications - Competent and experienced installers may charge slightly more but can ensure a high-quality job and potentially avoid future issues. 
  • Waste disposal - Costs associated with removing any existing render or cladding and disposing of construction waste. 

Additional Considerations 

  • Building Regulations - Obtaining any necessary building permits or approvals can add to the overall cost. 
  • Disruption - EWI can be disruptive, requiring occupants to vacate the property for some time. If temporary accommodation is needed, factor that into the cost. 
  • Unexpected Issues - During the project, unforeseen problems like dampness or structural issues might arise, leading to additional costs. 

Now let's suggest some figures to put this into context...

The average costs will look something like this:

  • Terraced house - £7,000
  • Semi-detached - £9,000
  • Detached - £17,500

To put it another way - and one that's perhaps easier to apply to your own case - you should expect to pay between £100 and £250 per square metre.

In reality, installing EWI on a large detached house could cost around £22,000, while a small flat would cost £6,000 or less.

Financial Assistance

If you are claiming benefits, on a low income, or live in a house with poorly insulated walls, you may be able to get help with the cost of external wall insulation.

The Great British Insulation Scheme provides funding for all types of insulation to help reduce energy bills. In some cases, the full cost is covered, meaning that you get your house insulated for free! However, most people will be required to pay something towards the cost, depending on their personal circumstances.

It's also worth checking with your local authority for any grant schemes, and you could check out the Energy Company Obligation (ECO) scheme. These can also help with heat pumps, loft insulation, etc.

Gain insights: Can You Get A Grant For External Wall Insulation

Factors Affecting External Wall Insulation Cost

What Are The Benefits Of EWI?

While the above figures might seem surprisingly high, we need to weigh the pros and cons to gain some perspective.

So, here are some of the positives for you to ponder:

Reduced Energy Bills

One of the main benefits of EWI is that it allows walls to contribute to the thermal mass of the building. The insulation layer significantly reduces heat loss through the walls, which is a major contributor to energy consumption, especially in colder months. Less heat escaping means your heating system doesn't have to work as hard to maintain a comfortable temperature inside, leading to lower energy use and reduced heating costs. 

While the primary benefit is in winter, EWI can also offer some cooling benefits in summer. The insulation helps to keep the heat from outside temperatures from penetrating your home as easily. This can make your house feel cooler naturally and potentially reduce your reliance on air conditioning (if you have it), leading to lower cooling costs during hot weather. 

Increased Property Value

When you add external wall insulation, your home's Energy Performance Certificate (EPC) rating will likely improve. An EPC is a document that shows a property's energy efficiency and is a key factor considered by potential buyers. A higher EPC rating translates to lower estimated energy bills, making your home more attractive to buyers in the long run.  

Improved Comfort

EWI offers a range of comfort benefits that significantly enhance your living experience. One of the most noticeable improvements is the elimination of drafts. Drafty homes can be unpleasant and uncomfortable, but EWI seals gaps in walls, preventing cold air leaks and creating a consistent temperature throughout your house. Furthermore, EWI promotes more even heat distribution.  

Without insulation, walls act as thermal bridges, allowing heat to escape from warmer areas to cooler ones, leading to hot and cold spots. EWI creates a uniform thermal envelope, ensuring heat is distributed evenly and eliminating uncomfortable variations in temperature.  

Balance Your Home's Heat Retention

Additionally, EWI keeps your walls warmer in winter. Cold walls can be a major source of discomfort, but EWI acts as an insulator, minimising heat loss and keeping your walls warmer to the touch, creating a cosy living environment.

While the primary benefit is in winter, EWI also offers some summer comfort benefits. The insulation layer helps regulate indoor temperatures by preventing excessive heat from outside from penetrating your home as easily. This can make your house feel noticeably cooler naturally, especially during hot spells.  

Reduced Carbon Footprint

External insulation plays a significant role in reducing your home's environmental impact. By significantly improving thermal efficiency, EWI drastically cuts the amount of heat lost in winter. This translates to lower energy consumption for heating, leading to fewer greenhouse gas emissions associated with electricity or gas generation.

Furthermore, a well-insulated home with EWI boasts a higher EPC rating, signifying its energy efficiency. This not only benefits you financially but also contributes to the UK's overall energy goals and reduces reliance on fossil fuels. Many EWI insulation materials are even manufactured from sustainable or recycled resources.

Choosing a solid wall insulation installer who uses such materials ensures your project minimises its environmental impact. Finally, EWI is a long-lasting investment that offers continuous environmental benefits. With reduced energy consumption for decades, EWI contributes to a smaller carbon footprint throughout its lifespan. 

Additional Benefits

Having your home insulated externally can also improve soundproofing, reduce condensation and mould growth, and dramatically enhance the external appearance of your house!

Benefits Of EWI

External Vs. Internal Wall Insulation

If the external wall insulation cost is beyond your budget, you could explore the possibility of internal wall insulation (or internal solid wall insulation).

As the name implies, the insulating material is applied to your internal walls rather than the outside walls. Essentially, it does the same job and is often used when external wall insulation isn't a viable or practical option.

Internal insulation is generally cheaper, typically between £60 and £100 per square metre. However, you will lose some of the internal floor area, which can be a problem in smaller properties. Also, when you insulate walls internally, you may be limited as to what you can attach to them, and window frames, door frames, and skirting boards may have to be altered.

Internal Wall Insulation 1

In Conclusion...

While EWI may seem like a significant investment upfront, MisterRender is here to help you make an informed decision. The potential cost savings from reduced energy bills and the increased value of your property can make EWI a worthwhile investment.

Remember, a warmer, more comfortable home with a smaller carbon footprint is priceless. Contact MisterRender today for a free, no-obligation quote and see how we can transform your home with external wall insulation.

Let's make your house a haven of comfort and energy efficiency, together.

Mister Render

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