Spray foam insulation is made of polyurethane which is sprayed wet onto surfaces where it sets into a solid foam. The air pockets in the foam provide the insulation.

It’s most often used in lofts where the foam is sprayed onto the underside of sloping roofs. This is done instead of laying rolls of standard mineral wool insulation on the floor of the loft. Spray foam is also used to insulate under suspended floors.

Should I install spray foam insulation?

Probably not. CSE’s view is that in almost all cases installing spray-foam insulation carries considerable risks. We recommend that householders consider other forms insulation (such as standard mineral wool rolls) first.

If you do wish to go ahead with spray-foam insulation (see below for reasons why you might) we strongly recommend seeking independent professional advice.

Why do we say this?

There are several issues with spray foam insulation, many of which have been in the news recently.

Damage to the roof

Spray foam does not damage roofs directly. But by coating the underside of the roof it hides the rafters and roof lining from view. This can make spotting leaks or making necessary repairs difficult if not impossible. If there is a leak, the foam can prevent the roof timbers from drying out and cause them to rot faster than they would have otherwise.

A layer of spray foam will make a survey of your roof impossible. This may mean you can’t install solar panels should you wish to.

If spray foam is applied directly to the underside of roof tiles it can cause serious problems. A study by HSE suggests spray foam insulation causes timber decay in more than a quarter of all cases. 

Damp and mould

As with all insulation, spray foam can lead to issues with condensation damp if ventilation is not considered during installation.  Of the two types of spray foam (see below) closed-cell foam is more likely cause this than open-cell foam.  If your home has existing damp issues these will likely be made much worse by installing spray foam as effected roof or floor timbers will not be able to dry out and can rot. 

Reducing property values

You may find that installing spray foam reduces the value of your home. According to the Royal Institute of Chartered Surveyors and Which, the presence of spray foam can make homes harder to sell, particularly if a survey finds that the insulation has been poorly installed.

Damage to health

Harmful fumes are produced during the installation of spray foam insulation and in the days it takes the material to set. It is important to ventilate during this time and to clean up any dust and debris produced during installation. If the insulation is poorly installed, the dangerous chemicals can continue to leach out for a long time afterwards.

Cost

Spray foam insulation is much more expensive to install than standard mineral wool loft insulation that is laid on the floor of the loft. 

Removal

Spray foam insulation is very difficult to remove. And in some cases, you’ll have to replace any materials the foam was sprayed onto, such as roofing timbers. It is also practically impossible to recycle these materials or the foam itself, and safe disposable adds to the costs. The removal of the spray foam can also produce harmful dust or other chemicals. For all these reasons, removal of spray-foam insulation can be very expensive – in the £1,000s for most properties.

Risk to wildlife

In the UK, all bats are protected by law, and it is illegal to obstruct access to or damage bat roosts – including unoccupied roosts – in your loft. This is not practically feasible with spray foam insulation. If you are planning to install insulation in a loft with bats, we recommend you contact the Bat Conservation Trust who can provide free advice.  In Wales, contact Natural Resources Wales.

In listed properties

You must obtain listed building consent before installing spray foam insulation anywhere in a listed property. Given that spray foam is so difficult to remove (see above), this is unlikely to be granted.

So why on earth would anyone install it?

Notwithstanding the drawbacks described above, spray foam insulation can be a good option in some (rare) cases.

One of these is trickier spaces where it may be more complicated to lay down standard roll insulation. An example of this is under a suspended floor. Here, using spray foam insulation means that the floor can be insulated without having to take up the floorboards. This is much less disruptive.

And there are some benefits for using it on the roof, too. Because spray foam is applied to the underside of the roof, you’re not laying insulation on the ‘floor’ of the loft. This means it can be used as space for storage more easily.

If you do decide to go ahead, make sure that the installer does a thorough survey of your home beforehand. This should including testing moisture levels inside the timbers. Make sure they provide you with a written report. And they should also give you a guarantee for the work.

Look out for scammers

Rogue traders are known to use aggressive sales tactics to pressurise homeowners into installing spray foam insulation.

A tactic these scammers adopt is to tell homeowners that their current insulation is illegal or dangerous, or linked with issues such as damp and mould. The homeowners will be harrassed into making a quick decision, without being given time to change their minds.

Some homeowners who have been mis-sold spray foam insulation will then be targeted again a few years later by the same scammers telling them that the insulation is very dangerous, and they need to pay thousands of pounds to remove it as soon as possible.

It is important to remember that these decisions are never really that urgent. You always have time to think these things through – and discuss them with someone you trust. You can find more information online about scams from Citizens Advice and from Age UK.

The different types of spray foam

There are two types of spray foam: closed-cell and open-cell. Closed-cell foam is not vapour permeable, which makes it a better insulator but also means that moisture can’t move through it. This can lead to problems if moisture becomes trapped causing roof timbers or floor joists to rot.  Open-cell foam is more vapour permeable. It is more flexible and is better for sound insulation, but more fragile than closed cell foam. And it is less effective as an insulator, so you need a thicker layer of it.

If you already have spray foam insulation …

Be vigilant about damp and mould

As spray foam insulation can lead to problems with damp and mould, you may need to be extra conscious of combatting this. You can find advice on this on our condensation, damp and mould advice page.

Should I remove it?

Removing spray foam is difficult, disruptive and expensive. So take the time to carefully consider whether this is affordable, and whether removal is worth the cost and disruption. If you do decide to go ahead, chose a contractor who s accredited and trustworthy. A good place to start looking is trustmark.org.uk.

Remember that you may also need to pay to have standard loft insulation installed after removing the spray foam.