In this article

What is solid wall insulation?

Does my home have a solid wall construction?

Solid wall insulation costs

Energy bill savings of solid wall insulation

Carbon footprint savings of solid wall insulation

How to find a good installer

Other ways to insulate the home


Solid wall insulation is a common form of insulation that can be installed in the home and can help reduce heat loss, increase energy efficiency and lower heating bills, creating a more comfortable home in the process. It involves insulating either the external or internal walls of the home, and with one third of heat typically escaping through these walls, it’s one of the most important areas to consider when improving a home's level of insulation.   

While the installation costs are higher than other forms of insulation such as insulating cavity walls, the reduction on heating bills can be higher too. In fact, a detached home with solid wall insulation could save up to £375¹ per year on annual heating bills and reduce their carbon footprint at the same time, helping to combat climate change.

Read on to learn more about the costs, benefits and savings to help you make an informed decision.  


What is solid wall insulation? 

As we’ve mentioned, roughly one third of all heat loss in the home occurs through the walls, so to ensure as little heat loss as possible, the walls need to be well insulated. Solid walls have no gap so it’s not possible to fill these with cavity wall insulation, which is typically much cheaper.  

Instead, these walls can be insulated by adding insulating material to either the internal or external wall of the home. This material then acts as a barrier to maintain heat and keep the home comfortable during cold weather. It’s worth mentioning that when we refer to the “internal” wall of the home, this is simply the inner face of the homes main external wall, you wouldn’t need to insulate internal walls between rooms for example.   

There are some key differences and pros and cons for each option:

External solid wall insulation  

External solid wall insulation involves insulating the home from the outside. This involves a professional installer fixing a layer of insulation material to the existing external walls using an adhesive. This layer of material is then finished and covered over with a special type of weather resistant render (plasterwork) or cladding.  

The render or cladding comes in several different finish options including tile, brick slip and painted finish. These finish options help match the additional layer to the existing design of the home, with some installers even offering bespoke finishes. The work can be carried out to maintain the original look of the home or can be used to modernise the exterior of the home, in addition to the main benefits of reducing heat loss and increasing energy efficiency.  

Advantages 

  • It causes less disruption to your routine as all the work is carried out on the outside of the property. This also means there will be no mess on the inside of the home.  

  • Because the insulation is installed on the outside of the property, it doesn’t reduce the size of rooms. 

  • It can help reduce noise pollution and make your home more soundproof.  

  • It can increase the weather resistance of the exterior of the home. 

  • It can help reduce condensation and prevent damp patches.  

  • It covers any existing gaps in brickwork, which can prevent draughts.  

  • It protects your existing brickwork as this will be behind the render or cladding layer. 

  • It can increase the value of your home to potential buyers. Buyers want to purchase a home that is efficient and cheap to run, so the increased level of efficiency will be an attractive selling point. The same is true for internal wall insulation. 

  • You can choose whatever finish you want for the cladding or render layer so it’s a great opportunity to modernise and improve the exterior look of the home. 

Disadvantages 

  • Exterior wall tends to cost the most when compared to interior wall insulation.  

  • Planning permission may be needed to modify the exterior of the home. We advise to check with your local council planning department. 

  • It is usually not suitable for listed buildings.  

  • The work must be carried out by a professional and is not suitable for DIY (same for internal wall insulation).  

  • An external scaffold is usually required, which will add to the costs of install.  

  • If the existing walls of the home are damaged, these will need to be repaired prior to install.  

  • All external pipework and items such as satellite dishes would need to be replaced prior to install. 

Internal solid wall insulation 

The other option available is called internal solid wall insulation. This involves insulating the internal walls of the home, that is, the inside face of the home’s main external wall. It’s possible for these walls to be insulated internally by fitting rigid insulation boards to the wall or by fitting an additional stud wall, which is then filled with insulation material such as mineral wool.  

Rigid insulation boards: This is the first option and will be fitted to the internal walls of the home. These are typically made of plasterboard with rigid insulation material fixed to the back. The typical size of these boards falls between 60mm to 100mm in thickness with them being fixed straight to the wall with adhesive or ribbons of plaster. Additional fittings are added to hold the boards securely in place, and they will be sealed following install to prevent air leaking out. 

Stud wall: This is the second option and involves a studwork frame made from metal or wood being attached to the wall and filled with insulating material, most commonly mineral wool. This frame can then be plastered over to be redecorated to match the rest of the home. It’s worth noting that mineral wool is less effective than rigid insulation boards, so the filling will need to be at least 120mm thick. The studwork frame can also be covered in rigid insulation boards, to be more effective than mineral wool and increase energy efficiency further.  

Advantages 

  • It is the cheaper of the two options, costing less than insulating the external walls.  

  • It is easier to install and doesn’t require any scaffolding to be put up.  

  • It’s a much better option if you own a listed building or don’t want to change the outer appearance of your home.  

  • It is suitable if you live in a block of flats where the exterior of the property cannot be modified.  

  • The installation can be carried out in conjunction with other internal works in the home, such as having a new kitchen fitted. This helps to reduce labour and callout fees.  

  • The insulation can be done on a room-by-room basis, the entire home doesn’t have to be done at once. 

Disadvantages 

  • Any internal damp and mould problems on the internal walls will need to be addressed before installation. Without fixing this, your insulation will be less effective.  

  • The boards or stud wall will reduce the size and floor area of the rooms. You can expect the room size to be reduced by roughly 100mm on each side.  

  • All skirting boards, external fittings and door frames would need to be removed and reattached following the install.  

  • Can be quite disruptive and cause mess and noise on the inside of the home with all the work being done inside, although any good installer will ensure this mess is cleared up following install. 

  • All furniture will have to be moved away from the walls prior to install. Any carpet, wooden, or laminate flooring will also have to be re-laid following the install.  

  • It can make it hard to fix heavy items to inside walls (such as wash basins) – although you can buy special fittings to get around this.


Does my home have a solid wall construction?

The first thing to do when considering solid wall insulation is to find out if your home uses a solid wall construction, which is easier to do than you might think. If your property was built before 1920, it is highly likely to have solid walls. This was the most common form of construction up until 1920 when cavity walls started to become commonplace.  

The first thing you can do is measure the thickness of the external walls. If they are less than 260mm thick and look narrow, they’re likely to be solid. Secondly, you can check your Energy Performance Certificate (EPC), which will have the construction type listed. A final way to check is to look at the brickwork on the external wall. In the case of a solid wall construction, the bricks will be laid in an alternating pattern with some laid across the wall and the smaller ends visible, as you can see in the image below: 

Image of a solid wall construction and brickwork


Solid wall insulation costs 

When compared to other types of insulation, solid wall does have a much higher price tag. This is due to the extra work, materials and equipment needed to carry out the installation. Costs can vary slightly depending on the installer but the typical prices you can expect to pay for a standard semi-detached home in the UK are:² 

  • External wall insulation: around £10,000 

  • Internal wall insulation: around £8,200 

Insulation grants 

Heating and home improvement grants help homeowners to install certain improvements in the home. While larger funding amounts under the Green Homes Grant have been withdrawn, another scheme is still accepting applications. We suggest to check out the Energy Company Obligation (ECO), this is a means tested scheme designed to help with the cost of insulation. It’s worth noting that due to the high cost of solid wall insulation, this scheme would only likely cover a small amount towards the install, but it is worth having a quick look into to see if you’re eligible. 


Energy bill savings of solid wall insulation

While the initial cost of installation is quite high, there are some great savings that can be made on energy bills. These are the typical savings that you can expect from having properly insulated solid walls:³

  • Detached: £375 (£/year) 

  • Semi-detached: £225 (£/year) 

  • Mid terrace: £145 (£/year) 

  • Bungalow: £150 (£/year) 

  • Flat: £105 (£/year) 

Graph showing annual energy bill savings from installing solid wall insulation in the home


It’s worth noting that if switching to a green heating system such as an air source heat pump or hybrid heating, you will need to ensure a good level of insulation, so you may need to factor in the above insulation costs to this. 


Carbon footprint savings of solid wall insulation

Installing solid wall insulation is a great way to improve the energy efficiency of the home. As a result of having a greater level of insulation, less heat will be lost in the home, and the heating system won’t have to work as hard, producing less carbon emissions. This reduction in carbon emissions helps reduce your carbon footprint, fighting climate change.

The typical annual reduction in carbon emissions you can expect would be:⁴

  • Detached: 1.5 tonnes (CO²/year)

  • Semi-detached: 930kg (CO²/year)

  • Mid terrace: 590kg (CO²/year)

  • Bungalow: 620kg (CO²/year)

  • Flat: 425kg (CO²/year)

Graph showing carbon emissions savings from installing solid wall insulation in the home


So, while solid wall insulation can help you to save on your energy bills, it can help save the planet too. To help you visualise just how much CO² you could save, we’ll use the example of a detached home: the 1.5 tonnes of carbon emissions you could save is the equivalent of over 500 litres of diesel.⁵


How to find a good installer

Solid wall is a form of insulation that does need to be carried out by a professional, using specialist equipment. This equipment combined with the knowledge required mean that we would recommend it is only attempted by a trained installer.

As with all home improvement works, you will want to ensure that the work is carried out to a high standard, so finding a reputable installer is key. It is worth checking out the National Insulation Association (NIA) website, to find a suitable installer in the local area. All installers registered with the NIA must abide to a strict code of practice, giving you peace of mind that your install will be carried out to the highest standard.

As well as checking the NIA website, there are some other ways to ensure a quality install: 

  • Shop around: It’s always best practice to get 2-3 quotes from different installers in the local area. This will help to give you an idea of the general prices being charged and helps to avoid being overcharged.  

  • Look at previous work: Any supplier worth their salt will be happy to showcase their previous installs. Ask to see if they have any before-and-after images, particularly when considering external wall insulation. Check the supplier's website to see if they have any case studies of previous customers experiences. 

  • Look at reviews: We would always advise to check out previous customer reviews. Trustpilot and Check-a-Trade are two great places to start. 

  • Word of mouth: Check with friends or neighbours who may have had similar work done and ask for their recommendation.  

  • Check the ‘U-value' and materials used: You should always receive a detailed quote and confirm the specifics with the installer. You should ask for the ‘U-value’ of the insulation. This is the rate at which heat will pass through the wall after the work is done. This should be no more than 0.30 watts per square-metre kelvin – the lower the better. You should also check which insulation materials they will use, and why they recommend them.  

Following these steps should help you find an installer that will complete the work to the highest standard, at a fair price. It’s worth checking if your insulation is guaranteed by the Solid Wall Insulation Guarantee Agency (SWIGA), who will guarantee the insulation for 25 years in the event of problems with design, workmanship or materials. It’s also worth checking that the materials used will be covered by a British Board of Agrément (BBA) certification


Other ways to insulate the home 

There are some other choices that can be made to insulate the home. These are all covered in our guide to home insulation, which include: 

Roof and loft insulation

A great deal of heat is lost through the roof and loft of a home, accounting for one quarter of total heat loss. It’s a really important area to consider when improving the energy efficiency of a home and could save you as much as £275 on annual energy bills.  

Cavity wall insulation

This is the construction of an inner and outer wall of the home, with a small space in the middle known as the cavity. This cavity can be filled with insulation materials to reduce heat loss, which could save up to £305 per year on annual energy bills. 

Draught proofing 

Draught proofing is another affordable option to reduce heat loss and increase comfort in the home. Measures to reduce draughts can include sealing skirting boards and gaps in windows and doors. You can typically save around £20 per year by increasing draught proofing in the home.


1,2,3,4 Source: https://energysavingtrust.org.uk/advice/solid-wall-insulation/

5 Source: https://www.epa.gov/energy/greenhouse-gas-equivalencies-calculator