How much does external wall insulation cost?

Find out what to budget for external wall insulation
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  • Adding external wall insulation to the outside of your house is an efficient way to reduce the amount of heating needed to keep your rooms warm and comfortable. But how much does it cost to get EWI installed and what can you expect to save in utility bills?

    External wall insulation is generally more expensive than cavity wall insulation and internal insulation. Nevertheless, if a qualified and vetted installer has surveyed your property and said it’s the best option, then it’s a great way to improve your home’s thermal performance. Here’s some guidance on what you need to budget for EWI and why quotes might vary.

    How much does external wall insulation cost?

    ‘Look to budget around £7,000-£15,000 for external wall insulation,’ says Nigel Donohue, CEO at Insulation Assurance Authority. That’s a wide margin to go by, but costs range massively as each installation is unique.

    Stats from the Energy Saving Trust (EST) correlate with this: it says the typical installation cost of external wall insulation on a three-bedroom semi-detached home is around £10,000. 

    When it comes to energy bill savings, the EST says fitting EWI could save you £255 a year (based on fuel prices as of November 2021). With household bills set to skyrocket, the cost of future utilities is unpredictable. You can be sure, however, that having external wall insulation will keep bills lower than leaving your walls uninsulated. 

    Gas bill with money on top

    Image credit: Alamy Stock Photo

    Remember that project costs will vary depending on the bespoke requirements of your house. The cost of the insulation itself isn’t the only thing to budget for, so find out what is included in any quotes to make sure you can compare like for like. 

    Here are the main factors that will impact on your total EWI project cost: 

    • Survey to assess what kind of insulation and finish is best for your home and any work needed prior to installation
    • Possible removal/replacement of elements on your home, such as pipes, guttering roof overhangs etc
    • Scaffolding for installation
    • Insulation type, wall ties & fixings
    • Wall finish, such as render, brick slips etc
    • Any new ventilation needed to maintain a healthy balance of moisture inside your home 

    How much does rigid board external wall insulation cost?

    external wall insulation

    Image credit: Alamy Stock Photo

    Rigid board insulation is typically a vapour-closed option, such as EPS, PUR or PIR. Supply-only, EPS boards generally cost around £9 per m2.

    ‘A full installation using 90mm-thick EPS on average costs £130 per m2, including all enabling work extending pipes and electrics, scaffolding, a 25-year guarantee, and a silicone rendered finish,’ says Danielle Belton, Director at Saving Energy UK. On a 100m2 property, that would come in at £13,000.

    How much does mineral wool external wall insulation cost?

    This is made of similar materials to the insulation rolls you see in lofts, but compressed to become rigid. Mineral wool EWI is generally more expensive than EPS – Danielle quoted £140 per m2 for all works, including a silicone render. That comes in at a total cost of £14,000 on our hypothetical 100m2 home.

    How much does wood fibre external wall insulation cost?

    Supply-only wood fibre render-carrying insulation boards cost around £19 per m2, which is twice the price of standard EPS. Installation needs to be done by people trained in using this system. So, you can expect to pay a little more overall, but you get the benefit of using natural, breathable and sustainable materials.

    How much does it cost to remove external wall insulation?

    If external wall insulation is fitted by a qualified professional that has used the correct materials for your home, then you are unlikely to face issues with your EWI installation.

    ‘It’s very unusual for EWI to need to be removed and cost can vary wildly depending on the type of system and what’s wrong with it,’ says Danielle Belton. ‘The only time I have ever known it to be removed is as a result of poor workmanship and the install not being completed properly. This is why it’s important to choose a qualified installer that offers an independent 25-year guarantee, such as from SWIGA or the IAA.’

    Is external wall insulation value for money?

    workmen installing external wall insulation with scaffolding

    Image credit: Alamy Stock Photo

    Installing external wall insulation is an expensive project and the likelihood is that it’ll take many years of fuel saving to get back your investment – if at all. Based on the EST’s figures, at bill savings of £255 it would take 39 years to recoup a typical £10,000 installation.

    A survey by the government in 2018, based on a small number of properties with retrofitted external wall insulation, saw property values increase by an average of 3%*. So, the money you’ve spent could make a difference to your home’s market price, but this isn’t guaranteed.

    It’s more likely that other improvements alongside the insulation project will increase the property value, such as changing windows, adding extensions etc.  Doing other work at the same time will offer better value for money, for instance, roof upgrades alongside mean you’ll only need to pay for scaffolding once.

    Is money your only motivator? Upgrading your home’s efficiency, especially when using natural materials, will drastically improve your property’s carbon footprint. So, if sustainability is at the heart of your renovation then you might see external wall insulation as good value for money.

    You’ll get the best result in terms of energy savings if upgrading the efficiency of your walls is part of a wider plan to improve your home’s the thermal performance. For instance, EWI might be stage one, with plans to add roof insulation and install renewable tech to run your central heating in the future. 

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