External Wall Insulation FAQs

External Wall Insulation FAQs

If you are interested in funded external wall insulation, click your area to see what's available:

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How much does external wall insulation typically cost?

EWI Typical Cost
Mid-terrace house £4,000 - £6,000
Semi-detached house £8,000 - £10,000
Detached house £12,000 - £14,000 +

What grants are available for external wall insulation?

Grants are available under the Government’s Energy Company Obligations (ECO) scheme. There are three types available:

Carbon Emissions Reduction Obligation (CERO) Grant

  • Available for every suitable home - no personal qualifications required

Home Heating Cost Reduction Obligation (HHCRO) Grant

  • You qualify for this if you are a homeowner or private renting tenant on certain state benefits

Flexible Eligibility

  • Social Housing with an Energy Performance Certificate rating of E,F or G can qualify for HHCRO funding under Flexible Eligibility
  • Local authorities that submit a statement of intent can qualify vulnerable residents for HHCRO funding regardless of their benefit eligibility under Flexible Eligibility

Find out more about funding options for EWI

How much external wall insulation save me on energy bills?

EWI - Typical Cost Savings on Energy Bills
Mid-terrace house £160 per year
Semi-detached house £255 per year
Detached house £425 per year

*Figures taken from the Energy Saving Trust

Can external wall insulation be used on cavity walls?

If you have cavity walls, in theory EWI could be put on top of it, but this would be unusual.

Cavity walls require cavity wall insulation, which is different from EWI. Cavity walls have built-in spaces within the walls where insulation can be injected into. EWI is installed on properties with solid walls with no cavities.

Cavity wall insulation is generally considered sufficient insulation and you shouldn’t have any need to add a different type of insulation on top. What’s more, funding for EWI will not be distributed if there is any evidence of cavity wall insulation in the walls you plan to externally insulate.

Can I get external wall insulation for free?

Sometimes – it depends on what opportunities there are in your area. Generally you cannot get EWI installed for free, but there are grants available which you could use to help with the cost. Some local authorities are running schemes that blend EWI grants with other sources of funding and in some circumstances installations are fully funded. However, for the majority of cases, grants for EWI will only support a proportion of the total cost.

Can I install external wall insulation myself?

We would never recommend you install EWI on your own, even if you are an experienced DIY-er.

EWI should always be installed by a specialist who has been trained by an approved system designer. What’s more, grants for EWI will only be issued if a PAS2030 accredited installer carries out the work.

In some instances, if you are experienced you may be able to install internal wall insulation yourself, though the rewiring and refitting of skirting boards and other features can turn that into a big job as well. If you do DIY internal insulation, you must make sure there is no damp in the walls – insulation on top of damp walls can make it worse.

Where can I buy external wall insulation?

Installers will buy the actual insulation product for you from an EWI manufacture and add this to the cost of the install. Contacting a company like YES Energy Solutions means we can help you with grant applications and finance plans as well as the installation. We work with market leading manufacturers, have a network of industry approved EWI installers and funding in place to support the cost of the work.

Does external wall insulation require planning permission?

Sometimes. EWI is considered ‘permitted development’ so typically does not require planning permission.

However, if you live in a listed building or a conservation area then you may need planning permission to get EWI installed. Some local authorities stipulate that planning permission is required if the outside of your house is going to change in colour or texture, which is often the case with EWI.

As a rule, we would recommend you always check with your local planning office before EWI is installed on your home. If a planning application is required, then it is highly unlikely that you will be refused.

You must apply for planning permission if:

  • The thickness of the insulation will mean your house infringes into someone else’s land or a public walkway or road
  • You live in a listed building
  • You live in a conservation area
  • Your local authority has strict rules about the colour and texture of properties in different neighbourhoods

Does external wall insulation add value to your home?

Yes, often it does. EWI will improve the visual appearance of your property adding to its resale value.

Better insulation will also improve your home’s Energy Performance Certificate (EPC) rating which is an influencing factor when selling a property.

According to researched published by the Government in 2013, moving from EPC band G to E or from band D to B can increase the value of your property by approximately £16,00 in England.

Here are the results from the report:

Average resale value increase when improving energy efficiency

*n/a means results were not statistically significant at regional level

Region EPC D to B EPC G to E
England average £16,009 £16,701
North East £19,265 £25,355
North West £12,979 £23,155
Yorkshire & Humberside £15,945 £17,298
East Midlands £10,936 £10,177
West Midlands £16,882 £9,282
East of England n/a n/a
South East n/a n/a
South West £16,342 £8,026
London £1,100 £41,808

Percentage resale value increase when moving from band G to any of these bands:

England average 14% 10% 8% 7% 6%
North East 38% 26% 23% 20% 15%
North West 27% 21% 18% 16% 12%
Yorkshire & Humberside 24% 16% 14% 12% 9%
East Midlands 16% 11% 7% 5% 3%
West Midlands 17% 10% 7% 5% 5%
East of England 7% 5% n/a n/a 4%
London 12% 12% 12% 11% 10%
South East n/a n/a n/a n/a n/a
South West 12% 7% 4% 4% 3%

Depending on your property’s current rating, EWI could help you move up an EPC band. On the first page of your EPC is a list of recommended energy saving improvements. The document also details what savings you are likely to make and what band your home would move to if all the improvements were implemented.

Find out if your home has an EPC.

How thick is external wall insulation?

The thickness of the insulation can vary depending on which EWI system you choose. Typically, EWI will add around 100mm to your house.

Is external wall insulation fireproof?

All quality EWI systems are fire retardant. This means they have been manufactured to achieve a very low combustion level which has been approved by an accredited fire classifications expert and deemed safe and fit for purpose.

YES Energy Solutions only install fire retardant EWI systems.

Many systems fitted throughout Europe have been categorised using the European Standard EN 13501-1. This is a fire classification procedure that grades materials based on their combustibility.

The grading covers three factors:

Factor Grading Information
1. Combustibility and contribution to fire level A - F A = Non-Combustable
B = Very Limited
C = Limited
D = Medium
E = High
F = Easily Flammable
2. Smoke emissions during combustion s1 - 3 1 = absent of smoke
2 = average intensity
3 = high intensity
3. Production of flaming droplets during combustion d0 - 2 0 = no dripping
1 = slow dripping
2 = high dripping

Many of the EWI systems YES Energy Solutions recommend and install have been graded ‘B s1 d0’ which is the highest fire retardant level within Euroclass B, and currently one of the best fire classifications for EWI systems on the market.

What is involved in a EWI fire test?

To gain a fire classification, the full EWI system must be tested by an authorised fire classifications expert such as BRE or ZAG. The full EWI system is fitted to a property and then tested for its combustibility. The examining organisation will grade the system on a number of factors including its contribution to fire, smoke emissions and production of flaming droplets/particles.

Systems that achieve the best fire retardant ratings are those with a very low combustion level.

What fire safety certificates are provided?

All quality EWI systems come with a BBA or ETA certificate. Listed on the certificate is the system’s fire retardant information including any details of fire classifications such as the European Standard EN 13501-1 grading.

You will be able to view your chosen system’s certificate before any work has taken place at your home. Copies can be obtained from the system manufacturer or from your installer.

Are thicker insulation boards more fireproof than thinner ones?

No – quality EWI systems are manufactured to protect the whole system and not just the insulation boards themselves. Therefore the whole system including: boarding, mesh, render and topcoat is tested to achieve the fire retardant rating.

Can external wall insulation fix my damp problem?

EWI is good at preventing damp but is unlikely to fix an existing damp problem. Insulating your walls is more of a deterrent than a solution to damp, so if there is already damage from existing damp then it is unlikely to get rid of it. This is particularly true for rising damp and penetrating damp, which are problems that need addressing before external wall insulation is installed.

Can external wall insulation prevent damp?

Yes, it certainly helps to prevent damp from occurring.

Insulating the outside of your walls helps to raise the temperature of the internal walls, thereby reducing the risk of condensation forming. It also provides a waterproof, protective barrier against penetrating damp.

How much can external wall insulation improve the U-value of my home?

When it comes to U-values, the closer it is to zero the better: this means very little heat will be lost through a given thickness of your wall material.

Current building regulations state that walls should have a U-value of 0.30 W/m2K, but solid walls (particularly in older properties) tend to have far higher U-values. The table below gives an idea of how much external wall insulation could improve this:

Typical solid wall U-value (225mm thick) before EWI is installed U-value after EWI is installed
2.70 W/m2K 0.29 W/m2K

Some EWI systems give a better U-value than others due to the materials used and the thickness of the insulation boards. However most EWI systems will give a U-value improvement of around -2 to -2.5, improving the thermal performance of your walls considerably.

Does external wall insulation improve breathability?

Breathability – which refers to a material’s ability to soak up and then release moisture rather than retain it – can be improved through insulation, depending on the type.

It’s important for walls – particularly solid walls in older buildings – to ‘breathe’ because this is key to avoiding damp and decay. Old walls in particular were often built with weak and porous mortars, plasters and renders, which absorb moisture from the air both inside and outside. So long as the moisture is then able to evaporate again, the wall can remain ‘dry’ and in equilibrium, which is why it must be allowed to breathe.

This is why it is recommended that you choose breathable materials, such as expanded polystyrene, to insulate solid walls as they allow for the continuous movement of air and reduce the risk of moisture build-up. YES Energy Solutions only installs quality EWI systems that offer a good level of breathability to maintain and protect solid walls.

What about airtightness?

A poorly insulated house often leads to air leakage, which can cause around 20% of energy loss in older homes. External wall insulation can reduce heat loss and improve airtightness by helping to seal off cracks and holes in the wall.

Will I still need to ventilate my home after having external wall insulation installed?

Once external wall insulation is installed, it warms the interior walls and moves the dew point outwards, which reduces the risk of condensation appearing on the interior surface. However, as with any house, additional ventilation may still be required to remove any moist air before it gets to the walls (e.g. through cooking, showering, etc). The system manufacturer and installer will be able to advise you on any additional ventilation requirements you may need to consider before installing the insulation.

Does EWI come with a guarantee?

Yes, EWI should come with a guarantee for both the installation and the actual product.

All quality installers will offer a guarantee for their labour. The manufacturers of the EWI system should also offer a guarantee. For example, SPSenvirowall currently provide a 12 year guarantee on their domestic systems.

If ECO funding is used to support the cost of EWI on a domestic property, a 25-year insurance backed guarantee should also be provided. This guarantee will be issued by your installer, but it will be underwritten by an independent insurer. This means that you are protected if your installer or system manufacturer ceases to trade in the future. The terms of your guarantee will still be met and honoured by the insurer.

What happens if something goes wrong, can EWI end up costing me a lot more in the long run?

External Wall Insulation is incredibly durable and long-lasting. It can easily last decades without any problems, and there is no reason to assume it will involve more maintenance or problems than any other rendered wall. In fact, in many instances it can protect your walls and you may never need to redecorate depending on the render that is applied.

According to experts from the Fraunhofer-Institute for Building Physics: “Damage or degradation of ETICS [external thermal insulation systems, otherwise known as EWI in the UK] façades are no more frequent than with conventional rendered masonry walls. A slightly greater susceptibility of ETICS to microbial growth due to rain or condensation water can be detected. Costs and frequency of maintenance for ETICS are comparable to those of traditional wall structures. The same holds for other durability aspects."

For this reason, it is unlikely that anything will go wrong with your system. If it does, you will be covered by a manufacturer’s guarantee on the product. This means the manufacturer will correct any issues free of charge, but will need to carry out a full survey before any corrective work is undertaken.

Are some EWI systems better than others?

There are various types of EWI systems available from different companies, such as SPSenvirowall, JUB, EWI-pro, Insta, Weber and Sto. These manufacturers will offer a range of EWI products suited to different properties and circumstances.

The higher quality EWI systems tend to be more expensive. There is no reason why you can’t have a conversation and a say in which system is used on your building, but it is worth heeding the advice of the installer. If a more expensive system is used it will increase the overall price of the installation.

Please note that most installers will have a relationship with a particular system manufacturer and may get a trade discount. We always recommend that you choose an installer that has been trained by the manufacturer and is accredited to fit your chosen EWI system.

What is the best EWI system?

It is important to choose a system that has full third body accreditation (such as BBA or ETA) and ensure that all main components are manufactured by the same company. Some installers may try and use parts from different systems to keep costs down, but this will compromise the quality of the insulation, so make sure the installer uses a single system.

Installers will have a preference to which system they consider to be the best for your home. For example, JUB Jubizol Premium is a well-known, quality system that is favoured by many of our installer partners. This system was used during our highly successful Redditch Borough Council EWI scheme..

Is external wall insulation worth the cost?

Considering the impact of cost savings from fuel bills, the value added to your home and the difference it will make to the environment and your carbon footprint, EWI is well worth it. Your house will be more energy efficient, feel warmer and look great!

Here are the average cost and energy savings:

Property Type Av Energy Saving (CO2/year) Av Cost Saving (per year)
Mid-terrace house 690 kg £160
Semi-detached house 1,120 kg £255
Detached House 1,870 kg £425

I rent a private property and it isn’t insulated – does my landlord have to insulate my house by law?

From 2018, all properties with new tenancies (including if you renew your tenancy but stay in the same place) will have to meet the Energy Performance Certificate (EPC) rating of at least band ‘E’ or above. In particularly inefficient properties, landlords will be obliged to make improvements.

Many solid wall properties, that are best suited to EWI, currently sit below the band ‘E’ rating, often falling into the ‘F’ or ‘G’ band, meaning they are less efficient than an ‘E’ rated property. That means that if where you rent isn’t insulated and has solid wall, you may well benefit from the new legislation, as EWI is likely to improve the property to band ‘E’ or better. So as a tenant, the new law presents a good opportunity to propose the installation of EWI.

However, keep an eye on news around the legislation (known as the MEES legislation), as there may be some loopholes which could alleviate the legal obligation for the landlord. In these instances it may be worth informing your landlord of just how much value EWI can add to a property. Moving from band ‘G’ to ‘E’ can add on average £16,000 to a property.

Alongside laws to be enacted next year, since 1 April 2016 a landlord is obliged to allow energy efficiency improvements where they are deemed “reasonable”. Reasonable is defined by the following criteria:

  • Can be wholly financed, at no cost to the landlord, by means of funding provided by central government, local authority or any other person
  • Can be wholly funded by the tenant
  • Can be financed by a combination of those two arrangements
  • Most funding programmes in the UK only partially support the cost of EWI, therefore in most cases a tenant would have to make a financial contribution to the installation
  • A landlord could choose to finance the work, however, so it may be worth discussing options with your landlord and highlighting the wider benefits of EWI

How much value is added to a property if EWI is installed?

EWI can help your property move up on the Energy Performance Certificate rating. According to a government report, moving from band G to band E adds, on average, £16,000 to the value of your property.

Where can I read reviews about EWI?

Take a look at our page collating first-hand experiences of EWI and reviews of YES Energy Solutions specifically: YES Customer Reviews

How long does external wall insulation last?

You can expect EWI to last for decades. In the UK, many systems have been installed with a 25 year guarantee, however quality EWI systems are designed to last considerably longer.

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