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Spray foam insulation

By Sarah Ingrams

Find out if spray foam insulation is right for your home, how much spray foam insulation costs, and the different types of spray foam.

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Spray foam insulation, also called spray foam, is an alternative to traditional building insulation that’s becoming increasingly popular in the UK. 

Spray foam insulation is versatile and can be used to insulate your roof, loft, walls and floor.

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.

What is spray foam insulation?

As the name suggests, 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 over 30 years and is now becoming increasingly popular as it’s an effective insulator and can also stop air leakage. But it's pricier than traditional types of insulation, such as mineral or glass-wool, polystyrene slabs or expanded polystyrene (EPS). 

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.

Should I get spray foam insulation in my home?

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, 100mm of spray foam insulation is equivalent to around 170mm of loft insulation, according to the National Insulation Association. Spray foam insulation is a better insulator than mineral wool loft insulation as you need less of it to get the same insulating effect. 

Some spray foam insulation sets rigid and can also be used to help reinforce roofs that are suffering from nail fatigue (when the nails used to hold slates in place rust) or support cavity walls where the wall ties are failing (causing cracks and bulges in walls). 

Some spray foam sets rigid and can help reinforce roofs or support cavity walls.

It’s also worth considering if you have hard-to-treat cavity walls or solid walls which aren’t suitable for external insulation due to planning restrictions.

Some types of foam insulation are waterproof but also breathable, so are suitable for homes in flood-prone areas. It’s still important to make sure your loft is properly ventilated though; check our advice on choosing an installer, below, for more detail.

But spray foam is more expensive than other traditional types of insulation, and you’ll need to get a specialist installer to fit it.

Spray foam insulation costs and savings

Spray foam insulation is not provided free by energy companies. If your loft or walls aren’t insulated, it’s worth checking whether you can get free insulation from your energy supplier first. 

Some energy firms offer this 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.

How much spray foam insulation costs depends on the thickness, the type (closed or open cell), the size of the area you want to insulate, and 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.

Spray foam insulation is more expensive than other types of insulation.

Spray foam insulation is more expensive than other types of insulation. The Energy Saving Trust estimates it costs around £300 to insulate the loft of a semi-detached house (three bedrooms). But it’s likely to cost over £1,000 to insulate the same home with foam insulation, and we were quoted £2,500 - £3,000 to insulate the loft of a three bedroom semi in southeast England.

As spray foam insulation is expensive, it means it will take much longer to pay back from the savings on your energy bills; over at least seven years (based on a cost of £1,000, saving you £140 per year on your energy bills.

Types of spray foam insulation

There are two types of spray foam insulation: open cell, and closed cell. 

Both 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. It 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 to stop condensation building up.

Open cell spray foam

Once set, open cell spray foam is less dense – you can compress it with your hand. So it can’t be used as a structural support. It’s not as good an insulator as closed cell foam, 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.

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.

Finding a spray foam insulation installer

Spray foam insulation should be installed by a professional, the National Insulation Association recommends. This is because 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 National Insulation Association recommends, to show it complies with Building Regulations.

An installer should carry out a survey before beginning the job. This usually includes a U-value calculation and condensation risk calculation. This shows how well-insulated your home is (a lower U-value equals better insulation) and assess the risk of condensation occurring in the structure of your home (interstitial condensation). It should identify any problems and what measures are needed to prevent them.

An installer should also use specialist software to calculate the thickness of spray foam you need - according to whether you’re looking for structural support or sound-proofing.

Applied incorrectly, expanding foam can put pressure on the structure of your home and risk damaging it. During installation, harmful fumes are given off which should not be breathed in.

You can use Which? Trusted Trader to find a recommended, local insulation installer.

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