Spray foam insulation: a full guide

If you want your home to hold more heat or reduce your energy bills, spray foam insulation is often touted as an alternative to traditional building insulation, such as mineral wool or fibreglass.

However, while spray foam might help raise the temperature in your home, it could also cause its value to plummet.  

Here, Telegraph Money explains what spray foam insulation is, how it works and the potential problems all homeowners need to be aware of.

• What is spray foam insulation?
• Types of spray foam insulation
• Problems with spray foam insulation
• Is spray foam insulation safe?
• Spray foam insulation and property value
• Spray foam FAQs

What is spray foam insulation?

Spray foam insulation involves using a liquid polyurethane foam to insulate your home. The foam is applied by professional installers using a spray gun. The material is sprayed on as a liquid, which then expands and sets to form an insulating layer.

As it’s liquid, the foam is quick to apply. It may also be easier to reach parts of your home that might otherwise be tricky to access and help with sound proofing.

Spray foam insulation can be used across the home – for example, in the roof, loft, cavity walls and floors.

The product has been in use for around 30 years but it seems to have fallen out of favour more recently. A BBC investigation found that a quarter of Britain’s biggest mortgage lenders refuse to lend on homes with spray foam insulation in the property’s roof space.

Types of spray foam insulation

There are two types of spray foam insulation:

• Closed cell spray foam: This option provides effective insulation with lots of gas pockets that slow the pace at which heat escapes. It can also help support the structure that it’s insulating. The catch is that it’s not vapour permeable, meaning moisture can’t escape – this can lead to issues such as condensation and damp.
• Open cell spray foam: This option isn’t as thick as closed cell spray foam, which comes with pros and cons. On the plus side, vapours are more able to permeate through it, so it is less likely to cause condensation issues. However, you’ll need a thicker layer of foam to create the same level of insulation as a closed cell option.

Problems with spray foam insulation

Spray foam insulation may be a versatile and effective way of keeping the heat in your home but it comes with a number of significant drawbacks that must not be overlooked.

• It can be expensive compared to other forms of insulation and needs to be installed by a professional.
• The spray releases chemical fumes during installation, and for a short period afterwards. These could cause health problems for some people.
• It may reduce ventilation, increasing the risk of damp, damage to timber and mould growth.
• The foam will conceal what is going on underneath it – meaning problems could be left to fester.
• It will be difficult to carry out roof repairs once installed, for example, after storm damage.
• It’s difficult and costly to remove.
• Thermal or ignition barriers may be necessary to meet fire safety standards.
• It may reduce the value of your home or make it harder to sell.
• Some less reputable installation companies may employ aggressive sales tactics.

Is spray foam insulation safe?

The fact that spray foam insulation involves using toxic chemicals means there are also a number of health concerns, including the risk of respiratory problems.

Harmful fumes may be released during the installation and curing process. For this reason you will need to stay out of your property for at least 24 hours after installation (48 hours for closed cell insulation). And there is a risk of off-gassing – that is, foam continuing to give off harmful fumes after installation.

People who already suffer from respiratory problems, allergies or certain skin conditions may need to take extra precautions.

Professional installers will wear protective clothing and use a respirator during the installation processes.

Spray foam insulation and property value

Normally, when you make an investment in your property – particularly if you are making it more energy-efficient – you expect it to increase the value of your home.

However, the problems associated with spray foam insulation means it could actually have a negative effect on your property’s value or make it difficult to sell.

The Royal Institution of Chartered Surveyors (RICS) warns that the presence of spray foam insulation “could affect a surveyor’s professional opinion of value” and they may need to commission an independent and specialist report.

Where the spray foam has been installed incorrectly or to a listed property without consent, it’s likely to have a detrimental effect on the property price.

If you already have spray foam insulation it’s important to make sure you have all the relevant documentation about its installation – including contracts, independent test certificates and guarantees – to reduce the risk of problems when you come to sell.

RICS has published a guide to spray foam insulation with advice for consumers.

Spray foam FAQs

Can you remove spray foam insulation from your home?

It is possible to remove spray foam insulation but it is likely to be difficult and expensive.

The Energy Saving Trust warns that the spray foam insulation is a permanent installation in your home. That means if you want to get rid of it, you may also need to bring down the structure it is attached to.

Will insurance cover a house with spray foam insulation?

Homeowners have been using spray foam insulation in their homes for decades. However, in recent years there have been reports that some homeowners have been denied buildings insurance for properties with spray foam insulation installed in the roof, due to concerns around structural damage.

Can I get a mortgage with spray foam insulation?

The Energy Saving Trust says that there was a period where the mortgage industry “reacted to concerns about damp and repairability”. Since then, it says there has since been progress around checking whether or not homes are at risk. As such, where spray foam has been fitted correctly, there should be less of an issue lending against the property. 

However, a recent investigation by the BBC found that a quarter of the UK’s biggest lenders wouldn’t mortgage homes with spray foam insulation in the roof.