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5 key problems with spray foam insulation and how to solve them

Spray foam insulation costs a lot, but it might be one of the best ways we currently have to insulate our homes. That doesn’t mean it’s free from problems, but most of these issues can be fixed.

We’ve looked into the 5 key problems with spray foam insulation and more importantly, how to solve them.

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Spray foam insulation can cause roof damage

Spray foam insulation, when done correctly, shouldn’t cause any significant damage to your roof. However, if you’ve opted for what’s called “closed-cell” spray foam in your roof, you do run certain risks.

Closed-cell foam is less porous than open-cell spray foam. What this means is that the warmth will have nowhere to go once it dissipates into your loft. This might not sound like a problem, but the greater warmth has a hidden danger – expansion and contraction.

When things heat up, they expand and subsequently, when they cool down the contract. It is this process of expansion and contraction that can cause damage to roofs.

Expansion and contraction causes gaps to appear in key parts of your roof, which decreases their structural integrity.

After a while of this process happening again and again, the likelihood of damage occurring increases.


How to fix

You can avoid this by opting for open-cell spray foam insulation, but as this type of insulation is not water resistant, any leakage from your roof could turn it into mush.

Alternatively, you might consider ventilation options such as a window (a roof window like a Velux is ideal for this), or a roof vent. The downside is that these add to the overall cost, but when you think about it, a new roof would be a lot more expensive overall!

On average, a single Velux window costs between £800 and £1,800, depending on the size of the window and location.

Wondering whether spray foam is worth the hassle? Check out our page Is Spray Foam Insulation Worth It? to find out.

It can cause bad smells

There’s a pretty unfortunate problem associated with spray foam insulation – bad smells, or more specifically, a fishy odour that seems to hang around for months after installation.

Whilst definitely an unpleasant experience for homeowners, the issue is thankfully rare.

For those unlucky enough to suffer from this, the cause is usually the fault of the installer. If they’ve applied the spray foam either too thickly, or too quickly, the reaction that causes the spray foam to expand properly is interrupted.

Applying it too quickly makes the exothermic reaction get too hot, meaning the next layer doesn’t react properly. When you apply it too thickly, the layer underneath cannot expand as it normally would, leaving gaps and causing the spray foam to again react incorrectly.

When the foam reacts in the wrong way, it gives off excess gas, which causes the nasty smell. Another reason for this is where the installer doesn’t use the correct mixture of chemicals.

This doesn’t automatically mean the installer is at fault, because oftentimes they just work with the chemical mix they’re given.


How to fix

The key way to avoid this issue in the first place is to make sure you get a reliable, professional, and well-regarded installer, one who knows how to install spray foam insulation properly.

If you’re already dealing with the issue, fixing it is challenging to say the least. You can’t simply ‘fix’ a bad chemical reaction without either removing the spray foam insulation entirely, or waiting for the problem to fix itself.

The latter is almost always a bad idea, because the sheer volume of material used in spray foam insulation means that the gases giving off the odour will linger for months (and in some really bad cases, years).

Removing the spray foam is also incredibly difficult, because of how effectively it clings to surfaces.

Other options include contacting the spray foam manufacturer, where normally you should be able to send a test sample of the insulation. They’ll see if they can determine the cause, but again, it’s not going to actually fix the problem.

Also, if you have your HVAC (heating, ventilation, and air conditioning) in your loft, there’s a chance that the ducts are leaking. This might lead to the bad smell being circulated around your home (again, the smell is still there, so even this isn’t a fantastic solution to the issue).

Mould and mildew is (sometimes) a problem

When you use closed-cell spray foam, you get a much tighter insulating seal, which keeps a lot more heat in than other forms of insulation.

The major potential downside of this is that, by keeping in so much warmth, you can create the perfect environment for mould and mildew to flourish.

Of course, mould and mildew is not a given with spray foam insulation – in fact it’s actually more likely for both mould and mildew to appear with fibreglass and fabric insulation.

One thing to note is that there is a conflict of interest between businesses promoting spray foam insulation, and businesses promoting alternatives.

The former insist that spray foam insulation is great for preventing mould and mildew, and the latter usually stress the opposite.


How to fix

Fixing mould and mildew is a case of trying out one of the many, many different recipes available online (bleach and water solutions are a popular option, or undiluted white vinegar if you prefer a more eco-friendly approach). Your best bet however, is preventing it from occurring in the first place.

For starters you should make sure when you get spray foam insulation, you don’t spray over surfaces that are showing the telltale signs of mould and mildew.

Both actually only take between 24–48 hours to appear, but at this point the growths can be small enough to miss entirely. So you should first assess your loft for any problem spots before committing to insulating it with spray foam.

Alternatively, if you use open-cell insulation, your roof will be able to ‘breathe’ more effectively.

It’s not eco friendly

Even though it’s a great tool to stop homes wasting energy (in turn, helping the environment), you can’t escape the fact that the majority of spray foam insulation is just not eco friendly.

In fact, it’s overwhelmingly made from materials that are not sustainable, so in the long run it’s difficult to see it as the catchall solution for insulating our homes.

Spray foam insulation is a petroleum-based product too, and as the world moves away from fossil fuels, things like spray foam insulation will inevitably become a thing of the past.

It isn’t just what spray foam is made from either – applying it has environmental risks that are hard to ignore. When you apply spray foam, you need to use a ‘blowing agent’.

These are commonly made from a mixture of hydrofluorocarbons and therein lies the problem.

Basically, hydrofluorocarbons have an incredibly high ‘Global Warming Potential’ (GWP). GWP is measured from a base level of 1, with carbon dioxide (CO2) from burning fuel defined as the start of the scale.

Methane (CH4) is well-known as being a good deal worse for the atmosphere than carbon dioxide and has a GWP level of 28. So this makes it 28 times worse for the environment than carbon dioxide.

How bad are hydrofluorocarbons then? Really, really bad – hydrofluorocarbons have an astonishingly high GWP level of 3,400, which would make releasing just 1 kilogram of the stuff into the atmosphere the equivalent of releasing 3.4 tonnes of carbon dioxide.

From a recycling point of view, spray foam insulation is pretty dreadful because of how it clings to roofing materials. This makes recycling any parts of your roof (for example during renovation or even a full roof replacement) very difficult.


How to fix

Spray foam insulation companies are keen to stress that their product is good for the environment. In terms of keeping heat in and stopping energy wastage, spray foam absolutely is. But you can’t escape from the fact that most spray foam is made from unsustainable materials.

An alternative to ordinary spray foam insulation, called Icynene, is promoted as a much greener option. It’s made from recycled materials and doesn’t contain any harmful gases, toxic chemicals, or synthetic blowing agents.

Most spray foams are applied using a toxic blend of highly damaging chemicals, but Icynene is applied using a 100% water-blown solution. This makes it a more eco-friendly approach to spray foam insulation.

It can cause health complications

Spray foam insulation is known to potentially cause a few health issues, including:

  • Asthma
  • Sensitisation
  • Lung damage
  • Other respiratory and breathing problems


How to fix

A lot of this comes from the excess gas left behind after installing the spray foam insulation. Homes will typically have to be evacuated for a minimum of 24 hours after installing spray foam insulation.

If the process isn’t done properly, the gas can continue to cause issues for a while afterwards, increasing the risk of the health complications above.

Next steps

Despite the issues, spray foam insulation is still a great way to insulate your home and lower your energy bills. It lasts a long time, meaning a good application could well keep your home warm for decades to come.

If you’d like to get started on insulating your home, why not fill in our simple webform? All you need to do is put in a few details and we’ll put you in touch with our trusted suppliers. Within a short while, they’ll contact you with free quotes for you to compare.

Frequently asked questions

For starters, it’s worth noting that not all mortgage companies dislike spray foam insulation. However, there are some mortgage companies that might not be open to remortgaging homes that have spray foam insulation because of the risks it can pose to the structural integrity of the roof if it’s not installed properly.

If an installer doesn’t apply the insulation (particularly closed-cell spray foam) properly, it can cause damage to the roof over time. This is because it expands as the home heats up, and contracts as it cools down. It can also increase the chance of mould developing, which can damage roof timber.

Spray foam insulation can last up to 80 years with the right maintenance, but this will depend on a few factors.

Proper maintenance for spray foam installed in the roof includes regular yearly inspections to fix any holes or cracks.

Like other types of insulation, spray foam insulation can be installed in the attic or roof, as well as under the floors, or in the walls.

It’s best to avoid applying spray foam insulation near electrical outlets or recessed lights (the type that are embedded in the ceiling) – if the foam expands, it can damage the electrical wires.

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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