External Wall Insulation: Pros & Cons, Costs, Grants

Over 21 million UK homes lack insulation, leading to 35% heat loss, making wall insulation essential for reducing energy costs. Wall insulation can save £140 to £700 annually and cut carbon emissions by 410 to 2,100 kg/CO2 yearly.

Among the various insulation options, external wall insulation is one of the most effective, especially for homes with solid walls. Although only 30% of UK homes have solid walls, a staggering 97% of these homes remain uninsulated. Exterior wall insulation is a powerful way to enhance energy efficiency for those with solid walls.

However, external wall insulation has its own set of pros and cons. It's a significant investment, with costs varying depending on your property's size and materials. Fortunately, several grants are available to help reduce the financial burden, making this energy-saving option more accessible.

In this article, we'll delve into the pros and cons of external insulation, discuss potential costs, and explore available grants to help you determine if this is the right solution for your home and budget.

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External wall insulation involves applying insulation to the exterior of your home, which is used explicitly on homes with solid walls. This method consists of several layers and includes:

External wall insulation is typically used for solid walls, commonly found in homes built in the 1920s or earlier. You can usually identify a solid wall by the pattern of bricks on your home. Solid walls have an alternating brick pattern, with some bricks laid across the wall so that the smaller ends are visible outside.

If your home is covered in a decorative finish, there is another way to determine whether you have external walls. Using a tape measure, measure the width of your wall. If the wall is 260mm or less, you will likely have a solid wall.

When considering external wall insulation for your home, it's essential to consider the advantages and disadvantages before deciding. Exterior wall insulation can bring significant benefits, such as improved energy efficiency and home aesthetics. 

However, it's essential to be aware of potential drawbacks, including higher costs and potential disruption during installation. By carefully evaluating the pros and cons, you can decide whether this investment matches your home's needs, budget, and long-term goals. 

Understanding these factors will help you make the best choice for your property's insulation needs. Here are the advantages and disadvantages of external wall insulation.

External wall insulation offers several advantages that can significantly improve your home's energy efficiency, comfort, and overall value. Here are some key benefits:

While external wall insulation offers numerous benefits, it's essential to consider the potential disadvantages before investing in it. Here are some key drawbacks:

External wall insulation costs on average around £11,000 for a semi-detached 3-bedroom house. Factors such as the size of your property, materials used, complexity of installation, finishing options as well as location will determine the overall price of your home.

Insulation specialists typically charge around £250 per person per day. Labour costs will increase for larger properties or homes with intricate architectural features, irregular shapes, or multiple stories due to the additional time required. Additionally, the location of your home will affect labour costs. Insulation specialists tend to charge more in larger cities where the cost of living is higher.

The type of external insulation material you choose will also affect the overall price. Here are the prices for the top materials:

Government grants for external wall insulation can significantly reduce the cost of insulating your home, making it a more affordable option for those of you on a budget. These grants support government initiatives to reduce carbon emissions, lower energy bills, and help households transition to more sustainable living.

To explore current grants and determine your eligibility, contact your local authority and visit your government's website to learn more about the requirements of each grant.

Choosing the right materials for external wall insulation ensures effective thermal performance, durability, and overall comfort in your home. Different materials offer varying insulation levels, moisture resistance, and ease of installation.

When choosing insulation materials, it's essential to consider several vital qualities:

In addition to these qualities, consider whether the material is sustainable and cost-effective to balance performance with environmental impact and budget. These factors help you select the best material for your external wall insulation needs.

When selecting the best insulation for external walls, various factors like sustainability, breathability, budget, thermal efficiency, and durability come into play. It's important to recognise that there is no universal solution, and you'll need to prioritise the qualities that matter most to you. Here's a breakdown of the top materials based on these criteria:

EPS boards are the most cost-effective material for external home insulation; on average, you will spend around £10 per m2. It provides a decent R-value at 4 to 4.5 per inch at a lower price point than other materials. While it’s less environmentally friendly than cork or wood fibre, EPS is lightweight, easy to install, and has good moisture resistance, making it a practical choice for those on a budget.

PIR boards have one of the highest R-values among insulation materials, ranging between 5.6 to 7 per inch, making them the most thermally efficient option. This material is fire-resistant and easy to install. However, it's important to note that the R-value can decrease in colder temperatures, and the material is susceptible to water absorption. Therefore, it is essential to have a sufficient water barrier and additional waterproofing when using PIR boards for external wall insulation.

Wood fibre insulation is very breathable, allowing moisture to escape while keeping the interior dry. It is an excellent breathable insulation for stone walls as it helps manage moisture, prevent dampness, and maintain structural integrity. It is also eco-friendly and burns slowly. However, it has a lower R-value than other materials at 3.5 per inch.

XPS is known for its high durability and compressive strength, making it suitable for areas exposed to mechanical stress. It is also highly moisture-resistant, which helps prevent water damage and prolongs the insulation’s lifespan. On average, XPS can last up to 50 years, but with proper installation, it can last a lifetime. It also has a high R-value of 5 to 6 per inch. It absorbs less than 1% of water, making it an ideal moisture-resistant material. However, XPS is one of the most expensive materials available at £21.50 per m2 and is highly flammable, releasing toxic chemicals as well.

Manufacturers make cork boards from the bark of cork oak trees, a natural and renewable resource. Harvesting the cork doesn't require cutting down trees, and the material is biodegradable, recyclable, and environmentally friendly. With an R-value of 3.7 per inch, cork boards are slightly more thermally efficient than wood fibre. In addition, cork is naturally resistant to fire and water absorption, making it an excellent choice for external wall insulation. 

When considering external insulation for your home, it's important to determine whether your walls are suitable for this type of insulation. External wall insulation involves adding a layer of insulating material to the outside of your home, which is then covered with a protective render or cladding. 

This method is highly effective for improving energy efficiency, but it is not suitable for all types of walls. Here’s a breakdown of which walls are most suitable for external insulation.

Many traditional homes in the UK have stone walls, often solid and either rendered or left with exposed brickwork. While some stone walls in older homes are solid, more modern stone walls may have cavities. It's essential to determine whether your walls are solid or cavity walls before proceeding with insulation. 

Traditional stone walls in the UK are designed to absorb and release moisture, preventing decay of the building fabric. Any insulation material you choose must allow this natural process to continue. Stone walls add character to a home, and adding external insulation could alter the aesthetic of your solid stone wall. Additionally, if you live in a listed building with solid stone walls, you may be denied permission for external insulation due to its impact on the building's appearance.

Solid walls consist of a single layer of brick, stone, or concrete with no gap between the interior and exterior. You’ll often find this type of wall in older homes, particularly those built before the 1920s, like Georgian, Victorian, and Edwardian houses. Because solid walls typically lose more heat than cavity walls, they are ideal candidates for external insulation. External insulation can significantly enhance thermal efficiency, reduce energy costs, and improve comfort.

Timber-framed walls consist of a wooden structural frame supporting the building, with various materials used for cladding or filling. Tudor architecture often features timber-framed homes, but they also exist in modern constructions. Between the 1920s and 1970s, builders constructed around 108,000 timber-framed homes.

Like stone walls, it's essential to determine whether your timber-framed walls are solid or have cavities, with more modern homes typically featuring cavities. Tudor homes, listed as buildings in the UK, cannot have external insulation added due to preservation regulations.

You can insulate timber-framed walls externally, but it's crucial to choose insulation materials that are compatible with the timber structure. To prevent moisture buildup and potential damage to the wood, external wall insulation installers often recommend using breathable insulation.

Approximately 284,000 homes in the UK are constructed from concrete, mainly built during the 1950s to 1960s. Although most older concrete homes are solid, newer homes made of this material may have cavities, so it's important to check the width of your walls to determine if they are solid.

If the walls are solid, they are suitable for external insulation. External insulation can help reduce the natural thermal inefficiencies of concrete or block construction, making the building more energy-efficient.

It’s generally not recommended to add external wall insulation to cavity walls. The reason is that cavity walls are designed to be insulated within the cavity itself, which effectively increases thermal efficiency. Cavity walls also have ventilation, which allows heat that penetrates the internal layer to escape into the atmosphere, rendering external insulation almost ineffective. 

Additionally, adding external insulation can cause issues like trapped moisture, leading to dampness and potential structural damage. While it is possible to add external insulation to a cavity wall, it is usually unnecessary and can create more problems than it solves.

When considering external wall insulation for your home, knowing the relevant building regulations is essential to ensure your project complies with legal requirements. Under the rules, if 25% or more of the exterior walls are insulated, they must meet current building standards.

In the UK, external wall insulation usually falls within permitted planning. However, some factors must be considered before starting this project. This doesn't apply to protected buildings or homes on a conservation site; planning permission is required for these types of homes.

Despite external wall insulation being considered permitted development, you still need to contact your local authority to assess if it falls under permitted planning.

Insulating external walls is a complex process, and it is considered one of the more challenging types of insulation to install. It involves adding a layer of insulation to the outside of your home, covered with a protective finish such as render or cladding. Here’s a simplified guide on how to insulate external walls:

While understanding how to insulate external walls is essential, DIY external insulation is not recommended due to the complexity involved. Working with reliable insulation specialists is vital. GreenMatch can connect you with top insulation specialists in your area. By filling out our 30-second form, we can provide up to four free quotes from the best insulation professionals. Click below to learn more.