Wall Insulation: Everything You Need to Know

It’s no secret that the UK housing market needs to be more energy efficient. As it stands, an astonishing 27% of the UK’s total carbon emissions stem from domestic energy alone. The biggest reason is poor home insulation, but perhaps the largest culprit of the batch is uninsulated walls, accounting for one-third of a home's heat loss. 

Wall insulation is an essential component of any home's heat-retaining capability and eco-friendliness. It helps maintain a stable and comfortable indoor temperature by slowing down the loss of heat through walls. This in turn leads to massive CO2 reductions, energy bill savings, and a comfortable living environment for decades to come.

In this ultimate guide, we will walk you through everything you need to know about getting wall insulation for your home, complete with types, materials, wall insulation costs, savings and grants.

Ready to slash your bills and carbon footprint with wall insulation? Let GreenMatch UK help you out. With our trusted network of professional installers, we can ensure that you get the best bargain for the job. Simply fill out our 30-second online form, and receive up to 3 free quotes, tailored to your home. No extra charges and no obligations apply. Click below to begin!

Wall insulation is perhaps the most effective and important insulation upgrade you could invest in to better your home. This is seen in the host of advantages that come with it, each that will improve your financial security and home environment. 

Here are just some of the key benefits you could expect:

The most common types of wall insulation available to you will largely depend on the type of wall your property has. In most cases, UK properties either have cavity or solid walls (depending on the age of your property) and an insulation approach best suited for it.

Now that we’ve got a brief understanding of the types of walls you are likely to find in the UK, let's have a deeper dive into the insulation process that takes place for each of them.

If you're wondering, what is cavity wall insulation? You're in the right place. Cavity walls are common and found in up to 71% of all domestic properties in the UK. They’re mostly seen in homes built after the 1920s and are made up of a brick outer wall and concrete inner wall with a gap or ‘cavity’ in between. 

Cavity walls can usually be identified by the brickwork of the property. If the outer bricks have an even pattern and are all laid lengthways, chances are it’s a cavity wall. 

Newly built properties will often have insulation material - such as rigid boards or batts of mineral wool - fitted into the cavity space during the construction process itself. However, the approach for insulating existing properties is different. 

Let’s have a look at how it’s done:

There are several types of cavity wall insulation, but the process is relatively quick and straightforward with plenty of pros, as well as some minor cons to consider. We’ve summarized the main points for you: 

Solid walls are less common in the UK and are mainly found in properties built before the 1920s. These are single or double-layered brick walls with no cavity space in between. Despite making up less than 30% of wall types in the UK, a staggering 97% of solid wall properties lack proper wall insulation and suffer from high energy bills.

Solid walls can also be identified by their brickwork. Normally, the pattern will be less symmetrical and contain brings that are laid lengthways as well as widthways.

The process of insulating solid walls is very different. Since there is no cavity space, these walls are insulated either internally or externally.

The process is more costly and labour-intensive to undertake and will require a professional installer to make sure the job is done correctly. 

External wall insulation involves fixing insulation material - such as rigid (sheet) insulation - on the outer walls of your property and covering it with render (plaster) and cladding insulation. 

While effective, a wall insulation board can be made from synthetic polymers and pollutants. A far more eco-friendly alternative is cork board insulation. Applied in the same way as insulation sheets, but derived from all-natural cork that is sustainably harvested.

An external wall insulation cost is indeed higher than inner wall insulation but comes with its pros and cons worth considering. Let's take a look at some:

Internal wall insulation is done by fitting rigid (sheet) insulation onto the inside walls of your home and covering it up with plasterboard, or by building stud walls and filling them with mineral wool or another wall insulation roll like fibreglass or sheep wool.

In both cases, any existing dampness and structural issues with the home will have to be addressed before undertaking internal or stud wall insulation.

The cost of insulating your walls can vary depending on the type of walls your property has, your home size, the installation complexity, and other property conditions. There are also several government grants and schemes in the UK to help homes upgrade their energy efficiency that you may be eligible for.

To begin with, let's have a look at a typical cavity wall insulation cost in the UK per property type:

Estimating the cost of solid wall insulation is far more difficult to do given the range of factors that influence the price. Nevertheless, a standard 3-bedroom semi-detached home in the UK could expect to pay around £7,500 for internal wall insulation, and up to £12,000 for external wall insulation respectively. 

A tip for reducing costs is to carry out insulation when you have other home improvements taking place. You could also insulate your home in parts rather than one go to ease the costs.

Now that we’ve got an overview of what costs we could expect for wall insulation, let's have a deeper look at some other cost-related factors that can influence your overall investment. 

For starters, the insulation material you opt for will have a big influence on your overall costs. Typically speaking, the more costly an insulating material, the more effective it is in retaining heat. Options like sheep wool and cork boards may cost more but are far more sustainable and eco-friendly than most synthetic counterparts.

Here is our full cost breakdown for average wall insulation material costs per m²:

Keep in mind that these costs can fluctuate based on the availability and thermal efficiency of materials. For example, low U-value insulation in the UK costs more as such materials are better at resisting heat transfer. Home insulation has been a forefront focus for homes all across the UK, and as a result, some material prices may increase if they’re in popular demand or difficult to produce.

There are available wall insulation government grants in the UK through two key schemes; The Great British Insulation Scheme and the ECO4 Scheme (Energy Company Obligation). Both initiatives aim to offer reduced-cost or free home upgrades to low-income and fuel-poor households throughout the country. Both schemes are currently active until March 2026. 

Let's take a closer look at each scheme:

In both cases, households in low-income categories, or those with an Energy Performance Certificate (EPC) rating under D are likely to qualify for cavity wall insulation grants, or solid wall grant options. If one or more members of a household receive certain government benefits, they may also be eligible for wall insulation assistance. 

In the UK, there are several regulations and requirements in place to ensure wall insulation jobs are carried out professionally and effectively. This also helps make sure that your investment is worth every penny. Here are some of the key points to look out for:

The best wall insulation material for the job will hinge on several factors, such as your wall type (cavity or solid), available budget, installation complexity and personal preferences. 

Nevertheless, some materials are better suited for certain wall insulation purposes than others, including some that can be installed DIY. In this section, we will break down the key wall insulation materials you can find, and which options are best suited for you.

Insulation rolls are blankets of woolly fibrous material that can be fitted behind stud walls when carrying out internal wall insulation. It’s generally the most affordable and market-wide available insulation material. 

Insulation rolls tend to be on the more eco-friendly side, with fully natural and sustainable options like sheep wool, or options with minimal environmental impact such as mineral wool (rock and glass) or fibreglass rolls.

Rigid boards are a range of insulation panels renowned for their high heat retention, making them one of the most effective insulation materials on the market. These are best used during internal or external wall insulation but are not suitable for cavity walls.

Most thermal insulation boards - like PIR or Polyurethane - are made from synthetic polymers that are energy-intensive to produce, difficult to recycle, and potentially unhealthy to live around. 

Luckily, eco-friendly alternatives like cork board are also available as a more environmentally conscious choice. Foil insulation board is another eco-friendly, cost-effective and easy-to-obtain alternative that is suitable for both internal and external insulation.

Spray foam insulation is a highly effective insulator when it comes to heat retention. It’s normally used in cavity wall insulation by being sprayed into the space through a series of externally drilled holes. 

Cavity wall foam insulation comes in liquid form and expands in the cavity space when applied. Unfortunately, it’s considered one of the least sustainable options on the market, often even containing toxic carcinogens like formaldehyde that are dangerous to live around.

While it’s true that a DIY insulation installation can cost two to three times less than a professional, there is no doubt that the benefits provided by a certified expert installer greatly outweigh the short-term financial gain of a self-done installation. 

For cavity wall insulation - or the use of insulation materials like blown fibre or spray foam - DIY insulation is simply not possible and a professional is required. As for all other cases where you can install insulation yourself, here’s why you should still consider a professional: 

While it’s evident that a professional installer is your best bet, finding one can be harder than expected. With the sea of professional installers available on the market, you could easily spend countless hours surfing websites and scheduling phone calls to land the perfect scenario. Here at GreenMatch UK, we want to free you of this stress.

Simply fill out our quick 30-second form and receive up to 3 free quotes from our trusted network of local accredited installers, completely free of charges or obligations to follow through. Click the button below to begin and land the best bargain for your home today!