Internal wall insulation is a great option in solid wall properties where external insulation is not practical or permissible; for example in listed buildings, conservation areas, where you wish to preserve the look of the building, where access restricts external work, or in flats.
How does internal insulation work?
There are a couple of methods to insulate a solid wall internally and all will decrease the floorspace of a room (as per the thickness of the insulation board or stud wall you use). We recommend getting a professional in to complete this type of work, and you do not undertake it as a DIY job unless you are very experienced.
An alternative to conventional internal wall insulation is using insulating wallpaper such as Wallrock Thermal Liner, which at only 4mm gives you some of the benefits of internal solid wall insulation, but has a far smaller impact on the size of your room. It doesn’t have the same insulating properties as proper internal wall insulation, but it is a much cheaper option.
Internal insulation and damp
Unfortunately, internal insulation will not be particularly effective against damp, when compared to external insulation. We recommend that any damp issues be dealt with before insulation is installed. All internal insulation should be installed with a vapour membrane.
Insulating directly to the wall
Fixing the insulation directly to the wall is ideal if floorspace is at a premium, but must only be done where there are no damp issues whatsoever, and the existing plaster is smooth and even. This approach is the most straightforward, as the plasterboard with insulation is attached to the wall using screws or adhesive. This approach requires a solid form of insulation such as Celotex or Kingspan, rather than wool type insulation. The table below shows the various U-values for different types of insulation.
Thickness of insulation
Polyurethane / Phenolic foam / Polyisocyanurate
Foamed glass (with plaster finish)
Insulating between battensSource: Energy Saving Trust
In this internal solid wall insulation method, timber battens are fitted between the wall and the plasterboard, with insulation between. This provides an optimum thickness of insulation and allows either rigid board insulation or wool type insulation to be fitted, making it a versatile and efficient way to insulate the wall.
Thickness of insulation
Polyurethane / Phenolic foam / Polyisocyanurate2
* Values assuming construction: 215mm existing solid brickwork with plaster finish (U = 2.1W/m2K) 1 Source: EST; 2 Source: Celotex
Source: Energy Saving Trust
Stud wall with insulation
This form of internal solid wall insulation is generally recommended for properties with uneven internal walls and those with damp issues. It also uses up the most internal floor space compared with the other options. This is because it leaves a gap of around 30mm between the outer wall and a stud wall, to which the insulation is attached. Timber stud can use many types of insulation with sheep wool, rock wool, Celotex or Kingspan fixed to the back of the plasterboard.
Reducing thermal bridging
It is really important that the installer avoids thermal bridging. With so much wood used in the installation, it is easy for this to form cold bridges, which allows the heat to dissipate from the room through the poorly insulated supporting frame. A good installer will avoid this by taking particular care around the door and window reveals, as well as the windowsill.
Cost and financing internal wall insulation
As a general rule, internal wall insulation will cost around £70-100 per metre, depending on the material you use.
Currently, internal wall insulation is being offered as part of the Green Homes Grant which last until March 2022. This grant covers up to £10,000 of the full cost, so it is worth looking in to!
Think we missed something? Do you have a different opinion?
If your house was built prior to the 1930s, the chances are that it will have solid walls – simply a solid layer of masonry bricks. Insulating your walls – regardless of whether they are cavity or solid (or even timber-framed) – is a great way to make your home more energy efficient. The insulation will minimise heat loss in the winter, saving you money on your heating bills. It will also stop your home getting too warm in the summer, helping to keep your home at a more comfortable temperature.
According to research, twice as much heat could be lost through an un-insulated solid wall as through an un-insulated cavity wall. However, the great news is that solid walls can be insulated, both internally and externally.
The science behind insulation
If hot air and cold air are partitioned by a wall, heat will transfer through the wall, eventually cooling the room until an equilibrium is reached (where the outside temperature is equal to the inside temperature). In reality this very rarely happens, because rooms tend to be heated; so as heat escapes through the wall, more hot air is supplied by your heating system, keeping it at a comfortable ambient temperature. If the thermal gradient is larger, for example on a cold and wintry day, the movement of the thermal energy across the wall will be accelerated.
Insulating a solid masonry wall helps to provide a thermal barrier, which helps to slow the movement of heat escaping out into the external environment. Less heating is therefore needed to keep the house at the required temperature.
Types of solid wall insulation for your home
Both internal and external insulation are great at keeping your home warmer, lowering your heating bills and cutting carbon emissions. However, both solutions have a different impact on your home, which is explained in the following section:
Internal solid wall insulation
There are a couple of methods to insulate a solid wall internally, which are either to use a rigid insulation board or build a stud wall. We recommend you get a professional in to complete this type of work, and you do not undertake it as DIY unless you are very experienced. Internal solid wall insulation can be as thick as 100mm, so your room will ‘shrink’ wherever it has an external supporting wall.
One way to avoid losing floor space is by using insulating wallpaper, which at only 10mm gives you some benefit of internal solid wall insulation, without impacting on the size of your room. However, the insulating wallpaper will not give you the same performance of dry-lining with the insulation boards unfortunately.
Advantages of internal wall insulation
Cheaper than external insulation
No aesthetic change to the outside of your home
Works well when the home itself is going through a process of internal renovation
Disadvantages of internal wall insulation
Will reduce the room you have in the living areas by up to 10cm, depending on the materials used
Won’t necessarily get rid of any damp problems, which need to be tackled separately
External solid wall insulation
For external wall insulation, you need to employ a professional and you also need to consider local building regulations. This is because this process involves covering the original brickwork and could significantly alter the current appearance of the property, making out of step with the local area. Once any planning permission has been granted, the home can be insulated using an adhesive material which is fixed to the wall, then plastered over.
The finish applied to the external wall can be any combination of texturing, painting, tiling, brick slips, masonry work and/or cladding.
Advantages of solid wall insulation
Less disruption to the household, as the work is carried out outside
Renews your home’s external appearance and increases the lifetime of the brickwork
Complements other refurbishment work
An opportunity to fill cracks and holes in the brickwork, which will help reduce draughts(see Draught Proofing for more information)
Disadvantages of solid wall insulation
More expensive than internal insulation
Planning permission may be required
Any work needs to comply with local building regulation
May not solve all damp issues
Work is not recommended if the building is not structurally sound
Costs of solid wall insulation
Additional costs for downpipes, gas pipes, boiler flues and dishes.
Subject to render strength – additional cost to remove old/weak render.
Potential requirement for scaffolding – around £15/m2.
Measuring the effectiveness of solid wall insulation
The R-value is the measure of thermal resistance used in the building and construction industry today. The higher the R-value, the better the insulating properties of a material – so you should be looking to insulate your house with materials displaying a high R-value. Confusingly, you may hear the word U-value also bandied around. This is exactly the opposite, describing the ability of a material to conduct heat, so you want your insulating material to have a low U-value.
Installing solid wall insulation
Interested in getting solid wall installation? Lucky for you, we work in partnership with EWI Store who specialise in external wall insulation systems! They have a great team who are always happy to help with your enquiries.
A home can lose as much as 35% of its heat through uninsulated external walls. By investing in cavity wall insulation, you can significantly reduce the heat loss from your home. The concept of insulating a cavity wall is really very simple – it involves filling the cavity between the two skins of masonry bricks with an insulating material, which slows the movement of heat through the wall. Maintaining the heat inside your home keeps you warm and cosy when you need to be. It also works in reverse by keeping your house cooler in the summer months.
Installing cavity wall insulation in your home will not only help to decrease your heating bills by saving energy lost through the walls, it will also help to reduce your carbon footprint by limiting the amount of CO² and other greenhouse gases emitted from your property.
Many houses since the late 1930s were built with a cavity between the inner and outer walls. Because of this cavity, many of Britain’s homes have thermal performances which are well below the standards required by current building regulations. These properties suffer from unacceptably high levels of heat and energy loss through the walls. A system was introduced in the 1970s to inject insulation into these cavity walls.
Can I get cavity wall insulation?
There are two things you need to determine to see whether you can benefit from retrofitting cavity wall insulation in your home.
The first thing is to work out if you actually have cavity walls – this might seem stupid, but you can not inject insulation if there isn’t a cavity and they do look quite similar to solid walls!
A cavity wall is made up of two masonry brick walls running parallel to one another with a space (cavity) between them of at least 50mm. Masonry bricks are very absorbent, so moisture absorbed by the outer wall typically drains through the cavity, rather than coming into the home, helping to prevent damp issues. This type of wall construction became the norm in the 1930s superseding solid walls and as time has gone on, the size of the cavity between the two skins of brick has continued to grow – a typical cavity wall now is between 280-300mm thick.
You can easily identify a cavity wall by the pattern produced by the brickwork, which is known as stretcher bond, where are the bricks are running in the same direction as one another – there are no ‘half bricks’. This is obviously harder to do if your walls are cladded or painted and in this case you might need to call in a professional (although sometimes you can see original brickwork in the loft space). In addition cavity walls tend to be over 250mm in width, with more recent cavity walls closer to 300mm. If you can see lots of half bricks in your wall, you have a solid wall with no cavity, so unfortunately cavity wall insulation is a no-go. In this case, you could look into external wall insulation as an alternative.
Once you have established that you have cavity walls, you need to determine the size of the cavity and whether it has previously been insulated. A registered installer will need to come and carry out a boroscope inspection. This involves drilling a test hole into the wall and checking with a camera to see if the cavity has previously been filled and the size of the cavity (ideally over 50mm). If this shows the cavity is unfilled, you could indeed benefit from cavity wall insulation.
Although some builders began insulating cavity walls in the late 1970s, it only became compulsory under building regulations to do so during the 90s. As such there are many properties in the UK that currently have unfilled cavity walls. The good news it that these can be insulated very easily!
How does cavity wall insulation work?
If a hot room is partitioned from the cold by a wall, heat will move through the wall, eventually cooling the room until an equilibrium is reached, where the outside temperature is equal to the inside temperature. In reality this very rarely happens, because rooms tend to be heated. This means that as some heat escapes through the wall, more hot air is supplied, keeping it at a comfortable ambient temperature. If the thermal gradient is larger, (e.g. on a cold and wintry day), the movement of thermal energy across the wall will be accelerated.
Insulating a cavity wall helps to provide a thermal barrier, which slows the flow of heat out of a room considerably. By slowing down the rate at which heat escapes from the home, less heating is needed to keep the house at the required temperature. In the summer, the reverse happens; hot air outside the home can’t get in as easily, which means you don’t need to use energy to keep the home cool. Therefore in both summer and winter, cavity wall insulation can make an enormous difference to your energy bills. The process is relatively quick and inexpensive, so it is certainly worth considering.
How do you insulate cavity walls?
The first thing to note is that you cannot retrofit cavity wall insulation as a do-it-yourself job – it is a job that needs to be carried out by a professional.
Once the cavity has been confirmed by the boroscopic inspection, the installer will drill a series of 22mm diameter holes into the mortar between the bricks. With specialist equipment, the installer will then inject the cavity with the insulating material, through each of these holes. Once the whole of the cavity wall has been filled, the mortar will be made good either with plugs or mortar created to match the existing colour, so the job will be barely noticeable.
The insulating material pumped into the cavity is normally a type of glass wool, or in some instances insulating beads and once installed will offer insulation for the life of the building. The whole process should only take about 2 hours but obviously if the cavity wall area is especially large you will need to leave more time for the job to be completed.
What materials are used for cavity wall insulation?
Expanded polystyrene (EPS) foam, loose polystyrene beads, or wool. EPS is the most expensive option for a reason; it is a premium product and we would always recommend spending the extra money for the best results.
Savings from cavity wall insulation
Although the savings from cavity wall insulation vary greatly from property to property, for an average size three bedroom home, the energy savings from installing cavity wall insulation should amount to £250 per year. With an installation cost of £600-1000, the savings you create from installing the cavity wall insulation should pay for the work in under 4 years.
Getting cavity wall insulation in the Green Homes Grant
If you are eligible, you can now get a grant of up to £10,000, using the Green Homes Grant scheme. The grants are available until March 2022 and are being offered to properties in England.
There are two grants within the Green Homes Grant. First is the £5000 which most are eligible for if they have cavity walls. However, if you are receiving one of the below benefits, then you may be eligible for the £10,000 grant.
Income-Based Jobseeker’s Allowance (JSA)
Income-Based Employment and Support Allowance (ESA)
Contribution-Based Employment and Support Allowance (ESA)
If you are interested in the Green Homes Grant, we advise you look at the Government website.
Paying for cavity wall insulation yourself
Unfortunately schemes like the Green Deal have now finished, but the Green Homes Grant is still available for cavity wall insulation.
If you are interested in getting cavity wall insulation installed, we work in partnership with EWI Store who have a network of approved installers. So please fill in the form at the bottom of this page, and we will be in contact with you shortly.
Insulating your cavity walls will help you to heat your home more efficiently, saving about £250 for a typical 3 bed home.
Cavity wall insulation will payback in 3 – 4 years for the investment giving lower heating bills .
According to the Energy Saving Trust, cavity wall installation can reduce carbon dioxide emissions (CO2) by 560kg, according to the Energy Saving Trust.
Approved cavity wall installation work is guaranteed for 25 years by the CIGA (Cavity Insulation Guarantee Agency).
Cavity wall insulation may not be suitable within your home, if it has a wall exposed to strong rainy wind.
Do not undertake the installation if the home suffers from damp problems – seek an assessment from a professional surveyor first
Cavity wall insulation can cost anywhere between £600 – 1000 (however with subsidies, the cost may end up at the lower end of this estimate – speak to your Energy provider).
Installing Cavity Wall Insulation
Need cavity wall insulation? We have scoured the country for the best tradespeople, so that we can make sure we only recommend those we really trust.
If you would like us to find you a local insulation installer, just fill in the form below and we will be in touch shortly!
Heating costs are on the up, and in the UK we have a challenge to keep warm whilst not spending an absolute fortune on our energy bills. In addition to this challenge (now into our 2020’s) as a nation we have stringent carbon targets to meet later on this decade.
With UK properties being one of the leakiest in Europe, external wall solid wall insulation is a fantastic energy efficiency measure to help up not only reduce carbon, but keep heating bill rises in check.
Why choose external solid wall insulation?
Most properties built prior to 1930 were constructed with solid walls, so they don’t have cavities that can be injected with insulation. These solid wall properties can be insulated with external solid wall insulation. The purpose of insulating in this manner is to slow the movement of heat out through the walls, thereby dramatically reducing heating demand.
The embedded video produced by us and one of our partners shows the typical external wall insulation installation process.
In most cases, homeowners get in a professional to install solid wall insulation; it is not normally considered a DIY job. Because the insulating process involves covering the original brickwork, the process can significantly alter the appearance of the property. Since the outside walls are highly visible, it is advisable to get someone who knows what they are doing to install it!
There are many types of insulation products that can be attached to the outside of the home: expanded polystyrene, mineral wool and phenolic resin (K5), woodfibre and even cork! Expanded polystyrene (known as EPS) is certainly the most popular, since it is the most cost effective means of carrying out the works. Phenolic resin (K5 boards) is used when space is a premium, since you can use less of this type of insulation to achieve the required U-value.
Mineral wool can also be used to insulate solid walls and some people choose it because it not only provides an open vapour system, but it is a great acoustic insulator. If it is picked for this reason, it is very important that no acrylic render is used to finish the project, since it is not breathable and therefore defeats the object!
You may choose to use woodfibre if you want the most breathable and natural insulation materials – however the system itself is very expensive compared to the EPS system.
External wall insulation must adhere to building regulations
When solid wall insulation is installed on the external walls of the home, it must adhere to building regulations. In this case it is referring to the thermal performance of the insulation; the solid wall insulation must achieve a U-value of 0.30 watts/m2k. With expanded polystyrene, this means that at least 90mm of insulation needs to be used – but obviously the thicker the material, the better its insulating performance.
For example, according to our competent U-value assessor, James Alcock a typical solid brick wall would require 90mm of the EPS system to achieve the desired retrofit building regulations u-value. Whereas to achieve the same value only 60mm of the K5 insulation board & system would be required.
For mineral wool you need 110mm of insulation to achieve the required U-value and for the the woodfibre insulation you would require 110-120mm of insulation to achieve the same energy efficiency standards.
External wall insulation sometimes needs planning permission
According to the planning portal, planning permission is not normally required for installing solid wall insulation, provided the external appearance of the property doesn’t change. If your property is brick and unpainted, changing its colour with render will require planning permission. Also, if the building is listed or is in a conservation area you should consult your local planning authority.
From our experience of installing solid wall insulation across London, it seems there is no standard approach to how the councils judge what is acceptable and what isn’t, so if in doubt, it is probably worth asking the question!
Firstly, if the property has existing render, a render test must be carried out to see if it is strong enough to hold the insulation. If not, all the existing render will need to be removed prior to attaching the insulation to the brickwork. If the render test shows that the existing render is firmly held in place, the render can simply be smoothed, ready for the insulation to be applied directly on to it.
Another important step prior to installing any external wall insulation is to remove any pipework from the outside of the building. These will be reinstalled at the end of the process (and maybe extended in some instances as necessary); this is one of main reasons that the insulating process is expensive and time-consuming.
Applying the external wall insulation and finishing
The process is relatively complex, but the basic steps are outlined below:
Insulating panels are fixed to the wall using adhesive mortar.
Plastic capped fixings are driven through the insulating panels and around their perimeter into the wall to tie the panels securely to the wall.
Mortar is then applied over the insulating panels and the fixings.
An insulating mesh is then sunk into the mortar to hold the panels in position.
The mortar is sanded and painted with primer to prepare it for the render
Below you can watch a video where we demonstrate how solid walls are insulated externally:
What external wall insulation and finishes are possible?
As the insulation goes on the outside of your house, it is important that you get the finish that you want.
A house pre and post solid wall insulation
On the whole, the most cost-effective way of insulating your solid walls is to finish it with a simple white render. However there is a huge variety of finishes possible: smooth, textured or painted, tiled, panelled, pebble-dashed or finished with realistic brick slips.
External solid wall insulation and damp
External wall insulation is a great way to protect against penetrating damp, creating a new weatherproof layer on the outside of the building, and slowing the movement of heat through the walls. Another advantage of solid wall insulation is that it will cause the temperature of the walls themselves to rise. This means if there is lots of water vapour in the air (from cooking or washing for example), this will no longer condense on these walls.
While obviously this is a benefit, it is still important to consider ventilation in the home – regardless of whether you insulate or not. This can be done by installing more vents or by making behavioural changes like opening windows and doors while cooking.
Cost and financing external wall insulation
The cost of solid wall insulation is roughly £100/m2, averaging between £6000 – £12,000 for a standard semi detached house, so it is not cheap. However, it can be really worthwhile in the long run. There are occasionally local council grants available for eligible people, and some companies offer finance so it is worth checking.
Currently, the Government Green Homes Grant is available to apply for if you meet the eligibility requirements. For external wall insulation, your property must be solid wall and it must be located in England to be eligible for the Green Homes Grant. The grant offers up to £10,000 off the full cost of the installation which will bring down the cost significantly, and in some cases the grant will cover the entirety of the cost. This scheme is running until March 2022, so there is still plenty of time to get your hands on it!
Advantages of external solid wall insulation
The insulation will take the U-value of your walls down to just 0.3w/m2k, equivalent to a brand new cavity wall built today – therefore your heating bills will be significantly lower.
Solid wall insulation stops penetrating damp.
The insulation can improve the appearance of your home – especially if you are replacing pebbledash.
It can also really help reduce noise entering the home, so if you live on a busy road it might be just the thing
Since the walls get warmer, they act as a heat store so rooms will take longer to cool down.
For a more detailed look at the advantages of solid wall insulation please click here.
Installing external solid wall insulation
Interested in getting external wall installation? Lucky for you, we work in partnership with EWI Store who specialise in external wall insulation and render systems! They have a great team who will be happy to advise you on any queries, and can help find local approved installers.
EWI Store are also helping with Green Homes Grant enquiries, and can help you find Trustmark approved installers who are offering the grant.
When installed correctly, cavity wall insulation is a fantastic way to help lower your energy bills. The insulation will slow the movement of heat across the wall and therefore your home will stay warm longer once you put your heating on, meaning you need to use less energy to keep your home at a comfortable temperature. It is for this reason the Government have traditionally been keen to promote the measure – after loft insulation, cavity wall insulation is the second most cost-effective energy saving solution.
In some cases though, cavity wall insulation simply isn’t the answer – the good news is that it can be rectified, the bad news is that there is a cost.
Why would you remove cavity wall insulation?
In the 1980s, building regulations stipulated that insulation should be installed during the construction of new buildings. As soon as these regulations came into play, it became clear there were a huge number of slightly older properties that could also benefit from this type of insulation; however the only way to get the insulation into the cavity once the property was built was to inject it. Since the materials were cheap and the installation process was relatively simple, the Government really pushed the measure. Thousands of small installer companies popped up, knowing they could install the insulation in people’s homes and be well paid for the work.
As a result, any property with an unfilled cavity was targeted, regardless whether it was suitable or not – so obviously issues occurred. Some of these issues are laid out below:
The insulation material used was unsuitable – e.g. urea-formaldehyde. The problems with this insulating product were two-fold: Firstly, it breaks down, releasing (carcinogenic) formaldehyde into the home. Secondly, when the insulation breaks down it falls down the cavity, meaning walls higher up no longer benefit from the insulation.
When cavity walls were first introduced in the 1930s, the cavity’s sole purpose was to prevent water crossing the wall from outside to inside, causing damp in the home. As a result the early cavities were very thin – insulation could cause bridges between the two skins of brick, allowing water to cross and leading to damp issues in the home.
The insulation was installed incorrectly. When the cavity wall installer puts the cavity wall insulation in the gap between the two skins of brick, the wall needs to be drilled in various places to allow an even distribution of the insulation. If the distances between the drilled holes were incorrect, then the insulation would not meet leading to cold spots.
Another issue was corner-cutting. Since installers are paid per m2 of wall, they need to do the jobs as quick as possible. When beads are injected into the cavity wall they are injected with a uPVC glue which binds all the beads together. The problem is that doing this properly – injecting the glue with the beads – takes about 3 times longer than installing the beads alone. Some installers wouldn’t bother, as they were looking to maximise profits by doing multiple jobs in the same day. This often led to beads ‘settling’ in the bottom of the cavity, meaning there was no real insulating impact on the upper parts of the wall.
Until the development of new technology, cavity wall insulation wasn’t suitable for every property. If a wall is privy to driving rain for instance, the cavity is required to prevent ingress of water into the home. If these walls were retrofitted with old-fashioned types of cavity wall insulation, it could quickly lead to damp issues – this is most prevalent in coastal regions.
Another example of a wall being unsuitable is when we hear of timber frame properties having had cavity wall insulation installed. These properties should never have cavity wall insulation installed. However an untrained or untrustworthy installer may have installed anyway to make sure they get paid for the job. We get several phone calls a month from homes who are in this situation and are trying to sell their properties, but are finding it impossible since mortgage companies won’t allow prospective buyers to get a mortgage on the property until the cavity wall insulation is removed.
The final reason is when someone has just bought a property previously installed with cavity wall insulation. In some cases, the insulation causes allergies for the new homeowner and again this needs to be removed despite the energy savings resulting from the installed cavity wall insulation.
The cost of getting cavity wall insulation removed is £21 – £22 / m2 depending on the material that was used in the first place, therefore for a semi-detached (which is 80m2) the price will be approximately £1,680 + VAT @ 20%. For a bigger detached property (so roughly 120m2) the price to remove the cavity wall insulation would be a £2,520 + VAT @ 20%.
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