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Home & garden.

16 August 2021

Spray foam insulation explained

Find out about the different types of spray foam, if spray foam insulation is right for your home and how much spray foam insulation costs.
Which? Team
Installer spraying foam insulation into place

Spray foam insulation, also called spray foam or spray polyurethane foam (SPF), is an alternative to traditional building insulation.

Spray foam insulation is versatile and can be used to insulate your roof, loft, walls and floor, helping to retain warmth and reduce energy costs.

Read on to find out whether spray foam insulation is suitable for your home and how much it costs compared with other types of insulation.

Spray foam insulation: pros and cons

Spray foam insulation offers a number of benefits, such as:

  • It can be applied in difficult-to-reach areas
  • In some cases, it can provide additional sound proofing.

However, there are also some significant drawbacks to consider, such as:

  • It’s more expensive than other types of insulation 
  • It needs to be installed by a professional 
  • It can be difficult to remove once it's been installed 
  • Potentially reduces ventilation within the roof space, causing humidity and damp; placing roof timbers at risk of decay 
  • Harmful fumes are given off during installation 
  • It shouldn't be used in listed buildings or houses with thatched roofs
  • It’s often ugly, messy and can’t be decorated over  
  • It can affect the value of your property – read on to find out more. 

We'd strongly advise getting specialist advice from an expert or two in this area and proceeding with caution.

What is spray foam insulation?

Spray foam insulation is a liquid foam which is sprayed into position and sets into an insulating layer. It can be used to insulate your roof, loft, walls, floors and more.

It has been in use for more than 30 years and is now becoming increasingly popular as it’s an effective insulator and can also stop air leakage. 

There are two types of spray foam insulation to choose from:

  • Closed cell spray foam
  • Open cell spray foam.

If spray foam insulation is right for your home and budget, the type you choose will depend on what you want it to do. Keep reading to find out more about the different types.

If you’re looking to insulate your loft, our dedicated guide explains the different types of loft insulation.

Types of spray foam insulation

Both open cell and closed cell spray foam insulation are usually made from polyurethane and filled with bubbles of gas or air, but have different properties when they set. We explain why you might choose one or the other.

Closed cell spray foam

Closed cell spray foam sets into a rigid solid, which can help support the structure of your property if it’s not in the best condition. That said, spray foam should never be applied as a quick fix where structural repairs are required.

Closed cell spray foam tends to be a better insulator than open cell spray foam. This is because when it sets, it contains lots of separate pockets of gas which slow down the movement of heat through it.

But it’s a barrier to moisture, so you’ll need to make sure your room or loft is well-ventilated. Otherwise condensation could build up.

Open cell spray foam

Open cell spray isn’t as good an insulator as close cell foam. It’s less dense once set – you can compress it with your hand. So you’ll need to install a thicker layer to get the same level of insulation.

Open cell spray foam is often used as sound insulation as it blocks and reduces airflow. It allows moisture through it so there’s less worry of condensation building up.

Why consider spray foam insulation?

One reason people don’t insulate their lofts is so they can store things in them. The required 270mm thickness of loft insulation is often higher than the joists, so you can’t lay boards on top. 

However, spray foam insulation doesn’t need to be as thick. 100mm of spray foam insulation is equivalent to around 170mm of mineral wool loft insulation, according to the National Insulation Association. This may allow you insulate your loft and use it for storage, too. 

But keep in mind that your roof needs to be in a generally good condition and not leaking. Otherwise spray foam insulation could cause new problems – see our advice on ‘Is spray foam insulation safe?’ below. 

Spray foam is also worth considering if you have hard-to-treat cavity walls or solid walls that aren’t suitable for external insulation due to planning restrictions.

Some types of foam insulation are waterproof but also breathable, making it suitable for homes in flood-prone areas. 

Depending on your property, it may also be possible to install underfloor spray foam insulation without lifting the floorboards. See our dedicated guide to floor insulation for more details.

Is my home suitable for spray foam insulation?

Every home is different and, since it's hard to remove spray foam once it has been installed, we'd advise getting specialist advice from an expert before proceeding.

An installer should always carry out a survey before beginning the job to ensure the product is suitable for your home. This usually includes:

  • a U-value calculation, which shows how well-insulated your home is
  • an assessment of the risk of condensation occurring in your home
  • identify any problems and outline what measures are needed to prevent them.

 Read more below in our section on 'finding a spray foam installation installer'.

Spray foam insulation costs and savings

Spray foam insulation is more expensive than other types of insulation, such as mineral or glass-wool, polystyrene slabs or expanded polystyrene (EPS). 

Depending on the size of your property, for example, you should expect to pay between £600 and £1,100 for professionally installed loft insulation using traditional materials, such as mineral fibre. And you could save even more if you installed it yourself. 

The National Insulation Association told us that typical costs for professionally installed spray foam loft insulation in a three-bedroom semi-detached property would be around £2,500.

The total cost will depend on the thickness, type (closed or open cell) and size of the area you want to insulate, as well as how it’s installed.

The National Insulation Association suggests a guide price of around £20 to £50 per square metre. The lower cost is for a thin foam layer for stabilisation, and the higher cost for a thicker insulating layer. Closed cell spray foam insulation is generally pricier than open cell. The difficulty of installation, type of roof and any repair work needed will also influence the cost.

Since spray foam’s higher cost means it will take much longer to pay back from the savings on your energy bills, compared to cheaper insulation.

If your loft or walls aren’t currently insulated, it’s worth checking whether you can get free insulation from your energy supplier

Some energy firms offer insulation to customers eligible under the ECO Scheme – for example, if you’re on government benefits or your home is among those which would most benefit from insulation. In some cases, it may be possible to get a grant to cover part or all of the cost of spray foam insulation.

Is spray foam insulation safe?

Unlike other types of insulation, spray foam insulation is formed on-site, which results in potentially harmful fumes being released. According to the National Insulation Association, the spray area should not be re-entered for a period of time after installation (usually 24 hours). An approved and trained installer will provide advice on all the health and safety considerations of the installation.

Beware of cold callers offering to install or remove spray foam insulation. Scammers often target vulnerable homeowners, falsely claiming that their existing spray foam insulation is dangerous and must be removed. Similarly, disreputable installers may make an unsolicited attempt to mis-sell you an unnecessary spray foam installation.

Poorly installed spray foam insulation can cause structural safety problems. By blocking ventilation, spray foam can result in severe condensation in the roof space. This can lead to rot in the roof timbers, which can go undetected for many years. 

Will spray foam insulation increase or decrease my home value?

As a result of concerns over condensation, spray foam insulation can end up causing problems when you’re buying or selling a property.

According to the Royal Institution of Chartered Surveyors, if a surveyor encounters spray foam insulation during their inspection, they may reduce the value of the property or request an independent specialist report. In some cases, spray foam insulation may even render a property un-mortgageable in the eyes of a lender.

The spray foam industry is currently working with lenders and valuers to try and resolve this issue. The National Insulation Association recommends making sure your installer provides you with all the relevant paperwork (see below), as this should help in the event of a dispute with a valuer.

Can I install spray foam insulation myself?

Because of the safety issues covered above, the National Insulation Association strongly warns against DIY spray foam installation. 

Spray foam insulation should always be installed by a professional. Installers must be trained to apply the foam correctly and should be assessed by the British Board of Agrément (BBA – a UK trade body which certifies installers’ competence). The spray foam product should also have a BBA certificate or equivalent. 

The installation must also conform with the manufacturer requirements, building regulations, and health and safety rules. Your installer should also provide you with the following:

  • details of the product installed
  • details of the company that installed the product
  • a product Agrément Certificate (BBA or KIWA)
  • a manufacturer or insurance-backed installation warranty for the work carried out.

Finding an insulation installer

Looking for a different type of insulation? You can use Which? Trusted Trader to find a recommended, local insulation installer.