Heat escapes through the exterior walls of many homes. This leaves families struggling with rising heating costs as they try to keep warm. Insulating these walls reduces heat loss significantly, which means lower energy bills. It also lessens environmental damage and increases property value.
Insulating exterior walls internally is one option. But is the cost worth the benefits? Find out here along with everything else you need to know about internal wall insulation.
Why Insulate Walls?
Without wall insulation, buildings lose one-third or more of their heat. So wall insulation is the most cost-effective way to start insulating your home. Adding a layer of insulation material to a wall traps air in small pockets and reduces heat transfer. This keeps more heat inside homes in cold weather. It also makes them cooler in summer.
Types Of Wall Insulation
Exterior walls can be insulated in different ways, depending on their structure. Uninsulated cavity walls lose up to 35 percent of heat. Insulating the gap inside the wall is the cheapest type of wall insulation.
However, most houses in the UK built before the 1920s have solid brick or stone walls. These include Georgian townhouses and Victorian and Edwardian terraces. Research has found that 97 percent of these properties lack adequate insulation. If these walls remain uninsulated, they allow about 45 percent of the building’s heat to escape.
The solution is internal or external wall insulation. Internal wall insulation (IWI) involves applying a layer of thermal-resistant material to the inside surface of a solid exterior wall. It may not be quite as effective as external wall insulation (EWI) – adding insulation material to the outside surface of the wall. But insulating walls internally costs less.
Internal Wall Insulation
There are four main ways to insulate a solid wall internally.
Stud Wall
Stud wall insulation involves fixing a wooden or metal stud frame to the internal face of an exterior wall and filling the gap with insulating material. The stud wall is finished with a layer of plasterboard so it can be decorated. This can be standard plasterboard or specially insulated plasterboard for extra thermal resistance.
Stud walls allow you to install heavier wall fittings than you can with insulation boards but they tend to take up more floor space.
Rigid Insulation Boards
Dry-lining with rigid insulation boards is a relatively new way to improve energy efficiency and thermal performance of exterior walls, by fitting them internally. They’re dense sheets typically made of closed-cell versions of polyurethane or polystyrene foam. These vary in thickness, with different thermal insulation capabilities.
Rigid insulation boards are durable and easy to install. Some have pre-attached plasterboard too, making the internal finish much nicer, much quicker.
Insulation Plaster
Thermal insulation plaster consists of standard plaster combined with insulating material such as cork. This makes it harder for heat to escape through your walls. Insulation plaster is trowelled or sprayed onto the wall and can be a good choice for uneven surfaces.
It’s typically applied in two coats and finished with a plaster skim that provides a smooth surface for painting or papering.
Flexible Thermal Lining
Flexible thermal lining consists of interwoven wood and textile fibres. Rolls of this robust and durable material are attached to walls with a special glue.
This method of internal wall insulation is easy to install and can be a good solution to preserve floor space in smaller rooms. The material is usually no more than a centimetre thick.
How Much Does Internal Wall Insulation Cost?
Internal wall insulation costs vary depending on the condition of the wall and the type of insulation. Nevertheless, insulating exterior walls internally is much cheaper than external wall insulation – less than half the cost in some cases.
Internal wall insulation can cost anything from £40 to more than £100 a square metre.
Depending on the size of your home, you can expect to pay in the range of £4,000 to £13,000 to insulate your exterior walls internally. But you’ll save hundreds of pounds a year on energy bills, and internal wall insulation pays for itself eventually.
Insulating walls of a standard three-bedroom semi-detached house costs on average around £7,500, according to the Energy Saving Trust.
This is £4,500 less than insulating solid walls externally. But it achieves around the same level of financial and environmental benefits. You’ll save about £380 a year on energy bills and reduce annual carbon dioxide emissions by 880kg.
Labour Costs
It’s inadvisable to skimp on the amount of insulation material in an attempt to reduce costs. Labour can account for up to 60 percent of the cost of internal wall insulation. This will remain largely the same whatever thickness of insulation is installed.
Zero VAT
VAT on installing wall insulation is zero-rated until March 2027, when it’s expected to go back to the reduced rate of five per cent.
Is Internal Wall Insulation Worth The Cost?
Older houses with solid external walls experience several issues related to energy efficiency as the interior face of the walls become cold and damp. You’ll see energy costs increase as you struggle to heat your home to a comfortable level. At the same time, carbon emissions increase.
Furthermore, the risk of condensation is greater. This can result in mould growth and rot – health hazards that can also damage the structural integrity of your home.
Internal wall insulation cuts fuel bills dramatically through better thermal performance and will eventually pay for itself. It’s also a lot cheaper than external wall insulation, with several other key benefits, including:
- Carbon footprint reduction. Homes in the UK are notoriously energy inefficient, emitting more carbon dioxide than cars. Internal wall insulation helps the environment by reducing these emissions.
- Healthier home. Internal wall insulation helps keep your home free from damp and draughts and improves air quality. This makes it healthier, with no risk of structural damage.
- Increased property value. Insulation improves a home’s energy efficiency credentials, which raises asking prices on the property market.
Furthermore, grants are available that cut internal wall insulation costs substantially or even cover the entire cost.
Internal Wall Insulation Grants
Low-income households living in poorly insulated homes can apply for a government-backed grant that will partially or fully cover the cost of installing internal wall insulation. This funding mainly comes from the Great British Insulation Scheme and the Energy Company Obligation.
Great British Insulation Scheme
The £1 billion Great British Insulation Scheme offers funding to households on low income who want to install internal wall insulation to improve their Energy Performance Certificate (EPC) rating. It’s open to a wider range of homeowners and tenants (via their landlord) than the Energy Company Obligation scheme covered below.
You don’t necessarily have to be receiving a means-tested state benefit but your home must have a low EPC rating (D or below for homeowners and E or below for tenants). Some households are able to install internal wall insulation for free while others pay a little towards the cost.
The Great British Insulation Scheme began in April 2023 and is scheduled to run until March 31, 2026.
Energy Company Obligation
The fourth and final scheduled phase of the Energy Company Obligation – the £4 million ECO4 programme – provides grants for internal wall insulation to low-income households struggling with fuel poverty.
Your home must have a low EPC rating and someone in the household is getting a benefit such as Income Support, Universal Credit, Housing Benefit, Working Tax Credit, Child Tax Credit, or Pension Credit.
ECO4 replaced ECO3 in August 2022 and, like the Great British Insulation Scheme, is expected to run until the end of March 2026.
ECO Flex Group
If you don’t qualify for internal wall insulation funding under the Great British Insulation Scheme or the Energy Company Obligation, you may be able to get help from the ECO Flex Group initiative.
Local councils set their own eligibility conditions for households not on means-tested benefits, so it’s best to check with your local council to see what discounts are available for your internal wall insulation.
Benefits And Drawbacks Of Internal Wall Insulation
Internal wall insulation improves thermal efficiency. This reduces energy costs by keeping more heat in your home, and it costs considerably less than external wall insulation. It also improves air quality in your home, eliminates drafts, helps prevent damp and condensation issues, and reduces noise from outside.
Furthermore, internal wall insulation can boost your Energy Performance Certificate rating and increase the value of your home. Well-insulated homes are more attractive to potential buyers and tend to sell at higher prices.
However, internal insulation isn’t quite as effective as external wall insulation. It also takes up floor space and the work can be disruptive, requiring removal and reinstalling of fixtures and fittings such as radiators, kitchen units, and light switches. This means the room can be out of use for a couple of days, so it may be a good time to get other home improvement work done too.
Planning Consent Considerations
Internal wall insulation may be a particularly good option if you live in a conservation area or your home is a listed building. Owners of these properties may be unable to get planning permission for external wall insulation. Internal wall insulation usually doesn’t need planning consent because no changes to the property exterior are involved.
Stud Wall Vs Insulation Boards
Stud walls and insulation boards are the most effective ways to insulate exterior walls internally. Stud walls are stronger so they can bear the weight of heavier wall fittings such as cupboards and shelves compared to insulation boards. But they’re often thicker, which takes up more floor space. Finding the right balance for your home is the key here.
Internal Wall Insulation Vs External Wall Insulation
Internal and external wall insulation are both effective energy-efficiency measures that reduce heating costs and can add value to your property. When deciding between the two, there are several key considerations.
Internal Wall Insulation Pros and Cons
Internal wall insulation is a good option if:
- External wall insulation is ruled out because of access limitations or planning regulations.
- You want to insulate only one or two rooms, especially if the walls have few fixtures of fittings.
- You can afford to lose some floor space.
- You’re planning to redecorate anyway.
Disadvantages Of Internal Wall Insulation
Internal wall insulation involves a certain amount of inconvenience because the work is done inside your home. Fixtures and fittings, light switches and electrical sockets will need to be removed and reinstalled, and the newly insulated wall will need to be redecorated.
It’s not always possible to insulate all of the wall surface, so you may be left with cold spots, too. Internal wall insulation also reduces living space.
External Wall Insulation Pros and Cons
Benefits of external wall insulation include:
- Minimal disruption during installation.
- Could ultimately be cheaper than internal wall insulation when you factor in redecorating costs.
- Enhances your home’s exterior appearance and provides weatherproofing.
- Optimises external noise reduction.
Disadvantages Of External Wall Insulation
The main drawback of external wall insulation is that it costs substantially more than insulating exterior walls internally and doesn’t result in significantly more savings on energy bills.
Although external wall insulation is less disruptive than internal wall insulation, it entails extensive preparation work on the wall and may temporarily put telephone cables and satellite dishes out of action.
And external insulation boards are usually bulky. They can add an extra 50 mm layer to the outside surface of the wall, creating installation problems around doors, windows and roof eaves. This can increase the cost of the work.
Is Internal Wall Insulation Right for Your Home?
Insulating your house is a smart investment that improves energy efficiency and cuts heating costs. It also makes your home healthier, more comfortable, and increases its value.
Insulating your exterior walls is one of the most effective ways to start getting these benefits. If you don’t have cavity walls, internal wall insulation is considerably cheaper than insulating solid walls externally. And you’ll still get pretty much the same level of financial and environmental benefits.
However, the installation process can disrupt home life for a short time and you may lose some valuable floor space.
Leading national insulation specialists Effective Home can help you decide whether internal wall insulation is a good choice for your house. We can also advise you on the cost and help you find out if you can access a grant.
We can also help with external wall insulation. And if your home has cavity walls that lack adequate insulation, we can reduce your energy bills with our cavity wall insulation services, too. If you’re looking for insulation support, you’ll find it at Effective Home.
