External wall insulation can be a great way to improve the thermal efficiency of your property and reduce your energy bills.
Insulating walls externally, means that an insulation material is applied to the outside walls of a property. This is done to reduce the amount of heat a property loses through the walls.
Generally, it’s something that is done with older properties that have solid walls and where internal insulation isn’t feasible.
However, it’s possible to apply it to cavity walls, but given the insulation properties of this newer building method, it’s not used very often.
And while there are many benefits to it, there are also problems with external wall insulation (EWI) that you should be aware of if you are planning to buy a property that has it or consider putting it on to your home.
Faulty Installation Can Lead To Issues With External Wall Insulation
Like with everything when it comes to home improvements, it’s important that the installation is done by a professional workman who is experienced and has the right knowledge.
To ensure the workman you are planning to hire is competent and experienced in carrying out the work check the following:
- Are they approved by any of the government recommended competent person’s schemes?
- Will they provide a warranty or guarantee?
- Get quotes from at least three tradesmen
- Check reviews or ask for details of previous customers so you can talk to them
The potential issues you could face if the installation isn’t done correctly are:
- Water ingress – if not all gaps are sealed properly, water could get in and damage the structure of the building
- Thermal bridging – incorrectly installed insulation can lead to heat loss and cold spots, defeating the object of installing it
- Condensation – cold spots can also lead to condensation, which can lead to mould growth
- Fire safety – depending on the thickness of the insulation, it could stop windows and fire exits from opening wide enough, causing fire safety issues
Thankfully, these issues can be avoided by ensuring that you get a competent installer.
Even If Installed Correctly EWI There Might Still Be Problems
The biggest issue homeowners might face is damp and condensation.
In fact, a study on Swedish properties concluded that the type of external wall insulation even influenced mould growth and instances of moisture damage (Hamid et al., 2024).
Older buildings are built either with solid brick walls or stone walls. The former tend to be impermeable, while the latter are mostly permeable.
- A wall that would prevent moisture on both skins (i.e. impermeable)
- A breathing wall, so moisture will penetrate – and then be evaporated away
Depending on which building material has been used, the insulation material used has to be chosen carefully so as not to cause issues.
Permeable walls will let moisture from inside pass through the walls, which will stop damp and condensation. If the walls are breathable, and you use impermeable insulation, any moisture that’s in the house will only get as far as the insulation.
This can lead to damp walls or insulation blocks, which can potentially damage the fabric of the wall if nothing is done.
A competent installer will be able to give you advice on which material is best to use.
If you do encounter damp or condensation problems after the installation, there are things you can do. Adding additional ventilation is one thing to ensure that the moisture from inside can get outside.
You can also use thermal lining paper in problem areas, as we did in our Wallrock thermal liner review.
Issues Around Doors And Windows
When you add insulation to your external walls, you basically attach thick boards to the walls. And when we say thick, we mean thick.
While the thickness will depend on the material that is used, you should expect the boards to be around 50mm (2in). Suddenly the wall no longer fits with the doors, roof eaves and windows.
This could lead to gaps that cause cold bridges. That’s where the cold can get to the walls, which can lead to cold patches in the house. This in turn can lead to condensation and mould.
But it’s also a place where the heat from inside can get out, reducing the energy efficiency of the insulation. It can be fixed, but will add to the cost.
It’s possible to use thinner insulation boards around these areas, also called reveals, but it will depend on the needs of your property. Make sure to hire a competent and experienced professional who can advise on the best solution for your home.
Building Regulations And Planning Permission
Another thing to consider is that you might need planning permission. This will only be necessary if your property is listed or in a conservation area.
Unless, the EWI will alter the appearance of your property, which could mean that you might also need planning permission. So it’s vital that you make sure if permission from your local authority is required before you start the work.
You can find a professional who can help you find out if you need planning permission or not by using the government’s handy tool.
If you are considering to go ahead without permission, be warned that you could incur a hefty fine and the local council could even order you to remove the insulation, meaning you have wasted your money.
While you might not need planning permission, you will have to adhere to current building regulations. If you engage a competent professional, you should be able to trust that they will comply to any regulations.
However, what’s most important is that you get a certificate proofing building regulations compliance at the end of the installation. If you don’t get this certificate, you can apply to your local authority to send an inspector to sign off the work.
This isn’t free of course, and there is a risk that the installation doesn’t pass which means you need to fix any issues brought up, which comes yet with more costs.
So it’s vital that you make sure that any professional you consider engaging to do the work will guarantee that you receive this important certificate.
Cost Of External Wall Insulation Can Be Quite High
One of the problems with external wall insulation is that it’s quite expensive. While the cost will vary depending on the size of the property and the type of insulation that is used, even at the lower range it will still set you back several thousand pounds.
- For a three-bedroom semi-detached home, the cost is likely to be in the range of £5,000-£9,000
- Larger detached homes could cost £8,000-£15,000 and there are specialist systems that come with a higher price tag, but there are also cheaper options available from builders’ merchants
So it’s important to get a few quotes from different companies before deciding.
In addition to the cost of the actual installation, you also have to take into account that scaffolding will need to be erected. And all pipes and cables fixed to the wall will need to be removed and replaced – costs that can’t be avoided.
Of course, if the insulation is fitted correctly, you’ll have a more energy efficient home, which will reduce your energy bills. But how much can you actually save?
Savings From EWI
It’s difficult to calculate the exact savings you could make, because it will depend on how much the energy efficiency has increased but also on energy prices.
And you shouldn’t forget that the insulation will also reduce the heat loss through the walls, which will make your home warmer.
However, you can expect on average to reduce your energy bills by the following amounts with correctly installed EWI:
- A detached home could save £425 per year
- A semi-detached home could save £255 per year
- A bungalow could save £170 per year
- A mid-terraced property could save £160 per year
- A mid-floor flat could save £125 per year
These cost savings provided by the Energy Trust are based on insulating a home with gas heating.
Of course, this means it will take years for the money you spent on the installation to be made back. But, in the meantime, you will have a warmer home that is more comfortable and that’s priceless.
And you also have to remember that when you come to sell your home, buyers will appreciate the improved energy efficiency. According to government research, EWI can even add value to your property.
The research found that the installation of external wall insulation increased the value by between 3% and 8%.
It’s Important To Weigh Up The Problems With External Wall Insulation
External wall insulation can provide several benefits to your property, but it is important to make sure that it is installed correctly to avoid any problems.
To ensure this it’s important to hire a competent and experienced installer who will install the EWI correctly and according to building regulations. And make sure you get a building regulations approval certificate.
Whether it’s worth installing insulation on your external walls will depend on your individual circumstances. It’s definitely worth considering the few problems that might occur and weigh them up against the benefits you will get.
