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Insulating Solid Walls Guide

Insulating solid walls of your home can be a great way to save money on your energy bills while also helping to fight climate change. It’s a win-win situation, and now is the best time to take action.

By insulating your solid walls, you could save as much as £540 per year on your energy bills, which is more than any other type of wall insulation.

About 28% of properties in the UK have solid walls, which means there are potentially millions of homeowners who could save thousands of pounds in both the short and long term just by adding insulation to their walls.

Insulating solid walls
Source: The Eco Experts

What is solid wall insulation?

Solid wall insulation involves adding a layer of insulation material to the exterior or interior of a solid wall. This type of insulation is suitable for homes that have solid walls made of bricks or stone without any cavity space for insulation.

If your home was built before the 1920s, it’s likely to have external solid walls, as well as internal solid walls. However, you don’t need to worry because even if your home is quite old, it’s still possible to install solid wall insulation.

In fact, solid wall insulation is often more effective in reducing your energy bills compared to cavity wall insulation.

How does insulating solid walls work?

The process of insulating solid walls may vary depending on whether it’s done on the exterior or interior walls, but the basic concept remains the same.

A professional installer will attach an insulating material to the visible part of the exterior or interior wall. The insulation material is then covered to ensure that the appearance of your home is not impacted. This insulation helps to prevent heat from escaping through the walls, which keeps your home warmer and more energy-efficient.

Insulating an internal wall

There are two methods of insulating an internal wall.

A professional can install rigid insulation boards directly onto the wall, covering them with plasterboard to ensure that the wall still looks presentable. Alternatively, they may build a stud wall filled with insulation if your wall is uneven or if there is a problem with damp.

In both cases, the result will be a layer of plasterboard that can be painted in a color of your choice. Keep in mind that the insulation is approximately 10cm thick, which could reduce your floor space. If a stud wall is necessary, this could exacerbate the loss of floor space, but it may still be worth it.

If your installer removes door frames, external fittings, and skirting boards during the insulation process, don’t be alarmed as it’s a necessary part of the procedure. They will reattach them once the insulation is complete.

After the walls are insulated, skimmed, and painted, be sure to use special fixings when hanging paintings or clocks because the walls are no longer solely made of solid brick.

Insulating an external wall

Insulating external solid walls involves attaching an insulating material to the wall, then covering it with render or cladding before adding a chosen finish such as smooth, tiled, painted, pebble-dashed, or brick slips. This insulation will make your home warmer and can be customized to your preferred appearance.

There are additional benefits to insulating external walls such as minimal disruption to your daily life, no reduction in floor area, improved soundproofing and weather resistance, and protection of the brickwork from the elements. Additionally, you’ll experience fewer draughts and less condensation.

If your external walls are easily accessible, you can simply check with your local council to ensure that it is permissible to proceed with the insulation project.

How much does solid wall insulation cost?

According to the Energy Saving Trust (EST), solid wall insulation costs around £12,000 for external walls and £8,500 for internal walls. 

To save money, it’s advisable to combine insulation jobs with other home improvement projects like installing solar panels or replacing windows. This approach will help you spread the costs over a more extended period.

The estimated cost of solid wall insulation is approximately £100/m², and it’s possible to measure your home to come up with an approximate amount. However, it’s still advisable to seek at least three quotes from professionals to obtain a more accurate estimate.

Below is a rough estimate of the cost of solid wall insulation for different types of homes, but it’s still recommended to seek professional quotes for your specific needs.

The costs for insulating solid walls mentioned earlier are based on homes that use gas heating, which is the case for the majority of UK homes as per government data from 2020.

Additionally, it’s important to note that insulating your home can increase its value by improving its Energy Performance Certificate (EPC) rating. In fact, a 2013 government study showed that improving your EPC rating from G to E by adding insulation could increase the value of your home by around £16,000.

Grants issued by the government

Currently, the Energy Companies Obligation scheme (ECO) is the only government grant available for solid wall insulation. ECO was established in 2013 to provide heat-saving methods, including solid wall insulation, to low-income households and individuals receiving certain benefits. 

Large companies are required to install up to 35,000 heating systems per year and help 15% of households in rural areas. You may be eligible for the ECO scheme if you receive benefits such as Pension Guarantee Credit, Tax Credits, or Universal Credit. 

The full list of eligible benefits can be found on the ECO website. It’s important to note that the Affordable Warmth Obligation scheme (AWO) is the same as the ECO scheme and may be referred to interchangeably.

Different Types of Insulating Solid Walls

There are several options available when it comes to solid wall insulation, including various materials and methods. Let’s take a closer look at the most common ones.


Insulation materials can be made from foam plastics such as polyurethane, polyisocyanurate, and polystyrene, or wool types like fibreglass and mineral wool.

Foam plastics are lightweight, durable, and moisture-resistant, but they are also flammable and can emit toxic fumes if they catch fire.

On the other hand, wool types are non-flammable, typically more affordable, and often come with an in-built vapour barrier to prevent dampness.

Internal Methods for Insulating Solid Walls

Insulating the inside of your home can be done using three different methods, with the first two being the most effective.

Rigid insulation boards

These are hard and lightweight rectangles that are fitted onto your wall before being covered with plasterboard. Some rigid insulation boards even come with the plasterboard pre-attached. 

Although they are typically more expensive than other types of solid wall insulation, they provide the highest level of energy efficiency and take up less space. 

They also provide soundproofing and can incorporate a vapour barrier to protect against damp. However, they are flammable and will produce toxic fumes if they burn.

Stud wall

Your installer will create a frame using thin columns of wood against your original wall. They will then fit one of the insulating materials mentioned above between the gaps and cover the result in a plasterboard. 

This option is helpful if your wall is rough or uneven, and you’d like it to be easier to paint and decorate. However, it may be more difficult to hang objects from than the original wall, and the use of wood makes it flammable. Additionally, this option will reduce your floor area more than other options.

Flexible thermal lining

This is a type of solid wall insulation that comes in rolls and can be attached to the wall using a specific adhesive. While it’s not as efficient as other internal insulation methods in terms of insulation, it’s generally less expensive. Additionally, it’s only about 10mm thick, which makes it easy to install without professional help. If you’re seeking a budget-friendly way to marginally enhance your insulation, this could be a suitable option.

External Methods

External insulation involves attaching insulating material to the outside of your home, which is then covered up with either plasterwork or cladding.


Plasterwork, or render, is a coating of plaster applied to the outside of your home to provide a smooth appearance after the insulating material is installed. It’s typically less expensive than cladding and allows you to paint the wall in any color you like. 

You could also choose to add pebbledash to the plasterwork to change the look of your home and make it more durable and resistant to wear and tear.


On the other hand, cladding is a dry material that is attached to your external wall with fittings or screws. It comes in a variety of options, such as wood, corrugated iron, and brick slips, giving you plenty of choices. 

However, you probably won’t be able to paint any of them. While cladding can give your home more protection against the elements, it is usually the more expensive option.

Get the right contractor for the job

Investing in solid wall insulation is a smart choice that can bring numerous benefits to your home and the environment. 

Not only does it improve the resistance to noise, damp, and cold, but it can also significantly reduce your energy bills and carbon footprint. Take action now and get in touch with a professional installer to discuss the best options for your home. 

By insulating solid walls, you can enjoy a more comfortable, efficient, and sustainable living space.

Looking For Plasterers In South London or Surrey?

Ralph Plastering is a highly recommended plastering company in South London and Surrey providing all aspects of plastering, dry lining, rendering and external wall insulation services.

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