Millions of families across the UK live in cold, poorly insulated homes with eye watering energy bills due to heat loss through walls. Wall insulation plays a key role in improving home energy efficiency and making life more comfortable. It also cuts heating costs, reduces environmental impact, and increases property value.
Walls can be insulated externally or internally. But which option is best? And which insulation method and material should you choose?
Find out here, along with everything else you need to know about the best wall insulation in the UK.
How Does Wall Insulation Work?
Insulating walls adds an extra layer that keeps more heat inside homes in cold weather. It also makes homes cooler in summer. It achieves this as insulation material traps air in small pockets, which reduces heat transfer through the walls.
Older houses may have no wall insulation. These properties lose one-third of their heat through the walls, according to the National Insulation Association. Insulation can be applied to the outside or inside of solid exterior walls. If your home has cavity walls, the space inside the wall can be insulated. Solid interior walls in older properties may also benefit from insulation.
Walls can be insulated in different ways with varying materials. Each method has its pros and cons.
How To Choose The Best Wall Insulation
Choosing the right wall insulation for your home involves several considerations. These include the age of your property, thermal resistance of the insulation material, and installation costs.
Property Age
The age of your home is an important factor when deciding on the best type of wall insulation. Most homes in the UK built before the 1920s have solid walls made of brick or stone. These include properties such as Victorian and Edwardian terraces and Georgian townhouses.
The walls of these houses need to “breathe” to avoid damp and decay. Breathability is the rate of water vapour transmission through the wall. Natural insulation materials such as wood fibre are best for retaining wall breathability. They absorb and release water vapour without negatively impacting insulation performance.
Thermal Resistance
To compare the effectiveness of various wall insulation materials, you need to know their thermal resistance, which is measured in R-values. This number tells you how good the material is at resisting heat flow. Insulation materials that perform better have a higher R-value.
And the higher that number, the more effective the insulation will be at preventing heat loss.
Insulation Costs
The cost of installing wall insulation often determines which method and materials you choose. If you can afford a more expensive type of insulation, it may offer better long-term savings in terms of energy costs and carbon emissions.
VAT on insulation installation is zero-rated until March 2027, when it’s expected to go back to the reduced rate of five per cent. And don’t forget insulation grants cut costs significantly or result in free wall insulation, so if you qualify, you ought to take advantage of this funding.
Solid Wall Insulation
Houses constructed pre-1920s are likely to have solid exterior walls rather than cavity walls. If your walls have an alternating long-short-long brickwork pattern, they’re probably solid walls.
Solid wall insulation costs more than cavity wall insulation but results in bigger savings on energy bills. Almost 50 percent of heat lost from a typical solid-walled house goes through the walls.
Solid walls can be insulated from the outside or from the inside.
External Solid Wall Insulation
External wall insulation (EWI) involves applying insulation material to the outside surfaces of exterior solid walls. It does something internal wall insulation can’t do – it stops cold bridging that causes insulation weak spots and condensation issues.
Types Of External Solid Wall Insulation
Solid exterior walls are insulated by applying a layer of insulation material to the outside of the wall and covering it with plasterwork render or cladding. Various finishes can be added. Types of external solid wall insulation include natural materials such as mineral wool or wood fibre, which are both breathable.
Rigid boards made of synthetic materials provide a further option. These include:
- Expanded polystyrene (EPS) boards.
- Polyurethane (PUR) boards.
- Polyisocyanurate (PIR) boards.
Pros And Cons Of External Solid Wall Insulation
External solid wall insulation is highly efficient and more effective than insulating the internal surface of the wall. It not only improves thermal efficiency by eliminating gaps and air spaces but also enhances the exterior appearance of the property.
If space is at a premium in your home, insulating walls externally will save valuable floor space that could be lost with internal wall insulation. However, external solid wall insulation is more expensive and may involve additional costs for fittings and fixings.
External Solid Wall Insulation Costs And Savings
Solid wall external insulation typically costs around £12,000 for a standard semi-detached house with three bedrooms.
The Energy Saving Trust says this can save up to £410 a year on energy bills.
Internal Solid Wall Insulation
Solid walls can be insulated internally by adding a layer of thermal material to the inside of the wall. This may reduce the size of the room but you’ll be more comfortable in the warmer space.
Types Of Internal Solid Wall Insulation
There are four main ways to insulate internal solid walls.
- Rigid insulation boards. These come in different materials of varying thickness, with different energy-saving properties. They include polyurethane, polystyrene, and foam insulation boards. Some have plasterboard already attached, which makes installation easier.
- Stud wall with infill. A metal or wood stud frame is fixed to the wall, and insulation material installed between the frame and plasterboard that’s fitted over it. Stud walls can bear the weight of wall fittings more easily than insulation boards but tend to take up more floor space.
- Flexible thermal lining. This comes in rolls and is attached to the wall with a special glue. Flexible linings tend to be no more than a centimetre thick – a good choice for smaller rooms.
- Insulated plaster. This can be a good option for uneven walls. A mix of plaster and insulating material such as cork is sprayed or trowelled onto the wall.
Pros And Cons Of Internal Solid Wall Insulation
Internal wall insulation (IWI) will certainly improve your home’s thermal efficiency but it’s not quite as effective as external insulation. However, it’s much cheaper to install so you might see a quicker return on your investment
Internal solid wall insulation may result in some loss of living space, and you need to bear in mind additional costs such as redecoration. Insulating solid walls internally can be best, however, if you need to retain the external appearance of your home – if it’s a listed building, for example.
Internal Solid Wall Insulation Cost And Savings
Internal solid wall insulation is generally less expensive than external solid wall insulation because labour and materials cost less.
Installing internal solid wall insulation in an average three-bedroom semi costs around £7,500 to £8,500 depending on the type of insulation material. Internal solid wall insulation can save you around £330 a year on gas heating bills.
How To Reduce Solid Wall Insulation Costs
The cost of solid wall insulation can be reduced if you carry out building or decorating work at the same time. External insulation will cost less, for instance, if scaffolding has already been erected for another job such as repointing or other repairs.
And internal insulation costs are likely to be lower if you coincide the work with redecorating or a remodel such as a new kitchen or bathroom. You can also spread the cost by insulating one room at a time.
You may be able to further reduce the cost of solid wall insulation with a government-backed grant. (More on this later).
Cavity Wall Insulation
Exterior walls of newer homes consist of two structures with a gap between them. These cavity walls usually have an even pattern with only the long edges of the bricks visible. The wall cavity is designed to stop rainwater penetrating inside the property. But it also allows heat to escape. This can be prevented by filling the gap with insulation material.
Nearly three-quarters of UK properties have cavity walls but 29 percent of them have no form of insulation.
Types Of Cavity Wall Insulation
Cavity walls are insulated from the outside by drilling small holes into the wall and injecting insulating material through them.
The main insulation materials used in the UK to insulate cavity walls are:
- Foam, typically polyurethane.
- Polystyrene beads and granules.
Pros And Cons Of Cavity Wall Insulation
Cavity wall insulation is one of the most long-lasting and cost-effective energy efficiency upgrades. It makes homes more comfortable, cuts energy bills, minimises carbon footprint, and reduces noise pollution.
Insulating a cavity wall is a simpler process than solid wall insulation, less disruptive, and costs considerably less. On the downside, insulating cavity walls reduces airflow, so additional ventilation will be needed to limit the risk of damp and condensation.
Cavity Wall Insulation Costs And Savings
Cavity wall insulation for a typical three-bedroom semi in the UK costs around £2,700. It can save up to £235 a year on heating costs.
Interior Wall Insulation
Insulating interior walls with no surface exposed to the outside keeps heat where you need it – in the rooms you’re actually using.
Types Of Interior Wall Insulation
Interior walls can be insulated with mineral wool, fibreglass, spray foam, cellulose, or rigid foam boards.
Pros And Cons Of Interior Wall Insulation
Insulating interior walls may lower energy bills to some extent and it makes homes more comfortable by eliminating damp, draughts and condensation. It also reduces noise transfer between rooms.
However, interior wall insulation is less effective than exterior wall insulation and can reduce usable living space.
Interior Wall Insulation Costs
Interior wall insulation costs on average £60 to £100 a square metre. There may be additional costs of £20 to £40 per square metre for plastering and decorating.
Wall Insulation Grants
Some homeowners and private tenants can get a government-supported grant that covers up to 100 percent of the cost of wall insulation. The main funding initiatives are the Energy Company Obligation, Local Authority Flexible Eligibility, and the Great British Insulation Scheme.
These funding programmes are open for the next couple of years but it’s advisable to apply sooner rather than later in case the money runs out.
Energy Company Obligation
The Energy Company Obligation requires energy providers to ease fuel poverty and reduce carbon emissions by funding measures such as wall insulation. It offers grants to low-income homeowners and private tenants on means-tested benefits who live in properties with a low Energy Performance Certificate rating of D, E, F or G.
The fourth and final phase of the scheme – the £4 million ECO4 – is scheduled to run until the end of March 2026.
Local Authority Flexible Eligibility
If you don’t qualify for an ECO4 grant, you may be able to get wall insulation funding from Local Authority Flexible Eligibility (LA Flex) – also known as ECO Flex.
This expands Energy Company Obligation grant eligibility. Local councils set their own funding conditions for low-income households who struggle with heating bills but don’t get a means-tested benefit.
Great British Insulation Scheme
Formerly known as ECO+, the £1 billion Great British Insulation Scheme (GBIS) enables 400,000 more households to get free or cheaper wall insulation. Funding is decided on a case-by-case basis.
You can apply for a GBIS grant whether or not you get a state benefit, as long as your home has a low Energy Performance Certificate rating. The scheme is open to households with an EPC rating of D or below in council tax bands A to D in England and A to E in Wales and Scotland.
Like the Energy Company Obligation, the Great British Insulation Scheme is scheduled to run until March 31, 2026.
Problems Caused By Poor Insulation
The UK has some of the oldest and least energy-efficient homes in Europe. More than one-third – almost 10 million – households across the country are living in badly insulated, cold and damp houses.
The English Housing Survey for 2022-2023 found that nearly half of homes had no cavity wall insulation or solid wall insulation. Poorly insulated homes have an Energy Performance Certificate rating of below C. Only 48 percent of UK homes have an EPC evaluation of A to C.
Poorly insulated homes allow unwanted heat transfer and result in draughts and moisture build-up. This leads to problems such as higher energy bills, cold spots, and excessive indoor humidity with potential water damage and health hazards such as mould and mildew.
Lack of insulation not only causes financial pressures and miserable living conditions; it also damages the environment. People in badly insulated houses use more heating to try to keep warm. Homes in the UK with gas- or oil-powered heating systems account for around 15 percent of the country’s greenhouse gas emissions.
Cavity Wall Insulation Vs Loft Insulation
Cavity wall insulation and loft insulation are both popular energy-saving home improvement measures. But many homeowners can’t afford both and have to decide which to prioritise, based on the initial cost compared with long-term savings.
If your budget is tight, loft insulation is the cheaper option. However, cavity wall insulation can save you more money than loft insulation in the long run. Consumer champion Which? says cavity wall insulation can pay for itself in nine months, while loft insulation can take as long as two years to reach payback point.
Final Thoughts On Choosing The Best Wall Insulation
Wall insulation results in better living conditions while cutting energy costs and reducing environmental damage. And if you decide to sell your home, you may be able to get a better price. Well-insulated homes appeal to homebuyers who prioritise energy efficiency and lower heating bills.
All this makes it well worth considering insulating your home’s walls when it comes to home energy efficiency options. But which type of wall insulation is best for your home depends on various factors including your budget and the age of your property. If you’re eligible for an insulation grant, you can install wall insulation for less or even at no cost at all.
Whether your home has solid exterior walls or cavity walls, a range of solutions are available to increase thermal efficiency. Insulating interior walls provides a further option.
Energy efficiency and home insulation specialists Effective Home can help you decide on the right type of wall insulation for your home. We can also help you find the best wall insulation grants.
