Reduce heat loss in your home, helping to cut your energy energy use and heating bills.
According to our research, around 33% of all heat lost in uninsulated homes escapes through the walls. By insulating your solid walls, you could save energy, lower your heating bill and make your home more comfortable.
If your house was built in the 1990s or after, it’ll likely to already have wall insulation to keep the heat in. You might not have any wall insulation at all if your house was built before then.
All walls have an ability to retain heat in your home; how good they are at this depends on the materials they’re built with. This also affects how much benefit you’ll get from insulating them.
This guide will tell you what you need to know, from understanding the type of walls in your home through to finding an installer.
The Warm Homes Plan is set to invest close to £15 billion in improving the UK’s homes to cut energy bills.
For people on low incomes, there’ll be fully funded government support to install insulation.
There’ll also be low and zero-interest loans available for homeowners regardless of income.
We’ll update this guide when we know more.
For more information, read our blog on what the Warm Homes Plan means for you.
The Warm Homes Plan is a pivotal opportunity to put right past issues and roll out a refreshed joined-up strategy that instils trust and confidence in households to upgrade their homes.
Stew Horne, Group Head of Sector Intelligence and External Affairs
Solid wall insulation is an extra layer that can help keep more heat inside your home.
Solid walls can be insulated either by applying insulation:
Before you can insulate your walls, you need to find out what sort you have. Most houses in the UK have either solid walls, or cavity walls, some have timber frames.
If your home was built before the 1920s, its external walls may be solid. Walls from that era were usually made of brick or stone, but they could also be made of earth.
Solid walls have no gap, so they can’t be filled with cavity wall insulation. It’s also possible that a pre-1920s house could be made of a timber frame with panels between the timbers.
If your house was built after the 1920s, its likely to have cavity walls. Find out more about cavity wall insulation.
If your house was built before 1920 and is made of stone, the walls are likely to be solid. However, some newer stone buildings have modern cavity walls.
If your house is made of brickwork that’s visible on the outside, look at the pattern of the bricks.
If your home has solid walls, the bricks will have an alternating pattern. Some bricks will be laid across the wall so you can see the smaller ends from the outside.
If your home has cavity walls, the bricks will usually have an even pattern with all the bricks laid lengthways.
If your walls are covered (for example with render or timber cladding), you should get advice from a building professional.
You might get a better idea of what type of wall it’s by measuring its width. You can do this by measuring the wall thickness from the inside of an open door or window to the outside.
Some houses will have a different type of wall structure altogether, such as:
If your walls are timber framed, the frame may be on show somewhere. However, it could be covered with render, cladding, or a newer masonry facing.
If you’re unsure what type of walls you have then it’s best to ask a specialist installer or other buildings professional. This could be an architect or surveyor. If they have experience of insulating your building type, they can also suggest options for how to add insulation.
All walls have an ability to retain heat in your home. But how well they do this depends on the materials they’re made of. This also affects how much benefit you’ll get from insulating them.
For example, a thin single brick wall or timber framed building will lose heat more rapidly than a modern insulated cavity wall. They’ll also lose heat quicker than a thick stone or earth one. Therefore, single brick wall or timber frame buildings might benefit more from being insulated.
Solid wall insulation might not be suitable for a few reasons if your home is:
It might also not be suitable if there’s a risk of your rooms overheating.
You should check for these risks should with an experienced installer or buildings professional.
Insulating solid walls internally or externally can:
Typical installation costs of solid wall insulation can vary depending on the size of your house and its walls.
Based on a typical three-bedroom, semi-detached house in Great Britain:
If you’re already making home improvements, then you might be able to reduce costs by carrying out the work at the same time.
The costs we give for installing solid wall insulation are based on:
If you want to spend less, you might want to have it done at the same time as other work. For example, internal insulation can be fitted when you’re planning to redecorate.
External insulation can also cost less if you fit it when you’re having other work done to the outside. This work might be:
With these jobs, you’ll probably have scaffolding already, so you can make the most of it by fitting external wall insulation at the same time.
It’s important to plan ahead and think about potential future work you’ll want to do throughout the whole building.
It’s crucial that you complete any repair and maintenance to the exterior of your building before adding any wall insulation. This includes:
Not doing these jobs first might trap damp or cause your insulation to fail.
You might be able to get funding or grants for insulation. Find financial support for energy efficiency in your area.
Here are a few things to think about if you’re getting solid wall insulation.
In properties with solid walls, traditional materials (such as brick, earth, stone, timber and lime) can usually manage moisture well.
This keeps it in balance with the surrounding environment, meaning damp never becomes a problem. This is because the materials are permeable, meaning they readily absorb and release moisture in response to changes around them. It might also be partly because of the high levels of ventilation caused by gaps in poorly fitting door or windows.
Energy efficiency improvements like solid wall insulation can affect this balance. This makes it important to consider moisture when fitting solid wall insulation to make sure you avoid damp problems occurring.
When you insulate an older building, you change the way that moisture behaves, both as liquid and vapour.
To avoid moisture issues, your installer should carefully consider the materials used. This includes:
You should check with your installer or another experienced professional about selecting suitable materials.
Your installer should also check:
Air needs to flow in and out of your house so it stays fresh, dry and healthy. It also helps prevent the build-up of moisture and damp in your home.
They shouldn’t block or seal any intentional ventilation such as:
A registered installer should also guarantee the work for 25 years. An experienced specialist building professional and/or installer can help you design a proposal tailored to your building.
Yes, it’s often possible to insulate an older or listed building in some way, where it’s appropriate to do so. When considering wall insulation for any property you should seek professional advice.
Insulation influences the building and its internal environment, including possibly increasing the risk of moisture build up or overheating within your home.
It’s particularly important to seek advice if you have a listed building or live in a conservation area. Some insulation options might change a home’s character or appearance, so insulating these properties will require some kind of permission. You should check with your local planning department to find out more.
Historic England has general advice for listed building owners looking to increase the energy efficiency of their home, and in-depth advice on installing insulation.
Historic Environment Scotland also has a guide on energy retrofit of traditional buildings
Welsh Government also has detailed guide on external solid wall insulation
Applying external wall insulation involves putting a layer of insulation material on the outside of the wall. This is then covered with a type of render (plasterwork) or cladding.
The finish can be smooth, textured, painted, tiled, panelled, pebble-dashed, or finished with brick slips, depending on what you need.
Benefits of external wall insulation include:
You’ll also need to think about:
Applying internal wall insulation to the external walls of your home involves:
Benefits of internal wall insulation include:
But there are still a few things you’ll need to consider with internal wall insulation.
TrustMark is a government-endorsed quality assurance scheme for work done in and around your home. Find a TrustMark-certified insulation installer via their find a tradesperson service. You should get at least three quotes to help find the best value.
Any TrustMark solid wall insulation company will offer a 25-year guarantee. This will either be backed up by an insurance company or provided through the Solid Wall Insulation Guarantee Agency (SWIGA).
Solid wall insulation is an effective way to cut heat loss from your home and save money on energy bills. You can also insulate other areas of your home to save even more.
Find out about other types of insulation and other energy efficiency measures.
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Last updated: 8 May 2026
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