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DIY spray foam insulation: is it a good idea?

DIY spray foam comes with significant health risks

Properly applying spray foam insulation requires a lot of experience

The average UK home will need more than one spray foam kit

Spray foam insulation costs a fair amount of money, so you may be wondering if doing it yourself is a good idea.

After all, properly insulating a home is one of the best ways to keep energy bills down, by helping homes waste less energy to keep warm.

We’ve investigated DIY spray foam insulation, looking at whether it’s a good idea, and what the advantages and disadvantages are to having it.

Read on for all our findings, but if you’re ready to start finding insulation quotes, why not fill in our simple insulation form now? Once you’ve entered a few details, we’ll put you in touch with our trusted suppliers and they’ll get back to you with free quotes.

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Man dressed in white protective gear applying spray foam insulation to a sloped roof.

Are DIY spray foam kits a good idea?

DIY spray foam kits are a risky endeavour at best, and downright dangerous at worst.

This is because the equipment needed to apply spray foam produces toxic chemicals that can be harmful if you’re exposed to them.

Asthma, other breathing problems and skin and eye irritation are likely if you come into contact with the chemicals before the spray foam has a chance to “cure” — the process of the spray foam mixture hardening.

Not only that, but you can do substantial damage to a property if you apply spray foam incorrectly. Spray too thick, and the spray foam might react badly, causing a nauseating smell that can last for weeks, if not months.

Also, using the wrong mixture for spray foam could stop it adhering to the roof properly. Spray foam applied correctly should last 30 years or more, so if it starts to crumble before this, the mixture was likely wrong when first applied.

The disadvantages of DIY spray foam insulation

It’s tempting to avoid the costs of paying an installer, but DIY spray foam insulation has clear disadvantages that you need to consider.


Bad odours

Spray foam insulation should stick to your roof and start expanding almost immediately.

If you apply it incorrectly however, it might not cure properly and this can lead to a nasty, fishy odour that persists for a long time.

This can make your home very unpleasant to live in and the worst part is, there is no quick fix.

The chemical reaction in botched DIY spray foam insulation will keep on reacting long after it’s been applied. Your only option in this case is to remove the insulation entirely, but trying to remove it comes with its own set of problems.


Damage to the roof

Spray foam insulation is designed to stick to roofing materials like a limpet to a rock. Once it’s applied, it becomes very difficult to remove, and attempting to do so can cause significant damage to your roof.

As well as this, poorly applied spray foam can cause excessive moisture build up, which can cause timber to rot. Rotting timber will eventually break down, meaning there is a real possibility that your roof could collapse.


Applying too thinly or thickly

The correct application of spray foam insulation requires spraying the mixture in just the right amount — spray too thinly and the spray foam won’t expand properly, spray too thickly and the reaction gets too hot.

When the reaction becomes too hot, the spray foam cracks and chars. It can also peel away from the roof’s joists, which leaves gaps in the insulation that’ll stop the spray foam doing its job properly.

This will also introduce a threat of moisture building up in the exposed pockets, running the risk of condensation damaging the roof and causing mould and/or mildew to build up.


Repairing roofs becomes difficult

Spray foam insulation makes roof repairs difficult, for a number of reasons.

Firstly, because it is designed to create a thick insulating seal, spray foam insulation is best left undisturbed. So repairing sections of a roof often means exposing the loft to the elements temporarily.

When this happens, the insulating seal can be broken. New roofing tiles cannot simply be placed on top of existing spray foam insulation, meaning you’ll probably need to reapply it.

Slate roofs can become impossible to repair too, as spray foam insulation often expands into the thin gaps left between each tile.


Health issues

Poorly applied spray foam insulation can result in chemical reactions that pose serious threats to health.

Known as “off-gassing”, fumes from a bad spray foam job have the potential to cause the following:

  • Respiratory problems
  • Asthma
  • Skin, nose and eye irritation

Breathing problems are the biggest threat and that’s what makes it essential to use the right respiratory gear when you apply spray foam.

The reason is that most spray foam mixtures using formaldehyde produce something called an airborne MDI (methylene diphenyl diisocyanate). These airborne particles increase the chances of developing cancer in those exposed to it.

Professional spray foam installers know exactly how to set up their protective gear to minimise their exposure to airborne MDIs. Even so, the best protective gear is no guarantee of protection.

This makes applying spray foam as an amateur a serious gamble, because most people don’t have the experience to know if their protective gear is 100% sealed against the harmful chemicals.

The advantages of DIY spray foam insulation

There are a handful of advantages to installing spray foam insulation yourself, even though we would always recommend hiring a professional.


Lower upfront costs

Buying the spray insulation kits yourself will keep some of the costs down, as you won’t be paying for professional installation.

The caveat is that you’ll likely need to buy more than one kit, as the roofing space of most properties in the UK exceeds what most single kits can cover.

A typical roof in a three-bedroom, semi-detached house covers between 65–75 square metres (m²). Looking around at spray foam kits online, the average coverage for a single kit is around 600 square feet (ft2), or around 55 m².

It’s a given that in most UK homes, one kit just won’t be enough. Cost wise, expect to spend £20–£50  per square metre covered.

Despite probably needing to buy more than one kit, it’s still cheaper than getting a professional to install. However, if something goes wrong, the costs could massively exceed what you’d have paid if you’d chosen a professional in the first place.

If you do hire a professional to install spray foam insulation, expect to pay around £2,500 to cover a three-bedroom semi-detached property. This is according to the National Insulation Association.

Check out our guide on spray foam insulation costs for more information on how much you could spend.


No need to wait for installation

Having your own spray foam insulation kit means you can apply it whenever it’s convenient for you. No waiting around for a contractor to come and install it.

It’s this convenience that tempts many people to do their own DIY spray foam insulation, even despite the risks.

It means that whenever you want to insulate your home with spray foam, you can decide exactly when to do so.

Next steps

While DIY spray foam is possible, it’s almost always better to get a professional to install it. The risks involved, including exposure to toxic chemicals and causing damage to your home, simply aren’t worth it.

It might be more expensive to hire a professional, but factor in the potential for damage caused by a DIY job and it’ll end up costing you a lot less to get it done properly.

To start finding insulation quotes, fill in our simple insulation form. All you need to do is enter a few details and we’ll put you in touch with our trusted suppliers. They’ll get back to you with bespoke quotes.

Written by:
Tom Gill
Tom joined The Eco Experts over a year ago and has since covered the carbon footprint of the Roman Empire, profiled the world’s largest solar farms, and investigated what a 100% renewable UK would look like. Tom has a particular interest in the global energy market and how it works, including the ongoing semiconductor shortage, the future of hydrogen, and Cornwall's growing lithium industry.
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