22nd July 2021
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.
Despite it being a flexible product that helps retain warmth, therefore reducing energy costs, there are some crucial drawbacks to consider, such as:
We'd advise getting specialist advice from an expert or two in this area before proceeding with caution.
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.
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:
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.
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 . 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).
But keep in mind that your roof needs to be in a generally good condition and not leaking, or it can cause new problems.
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, so are suitable for homes in flood-prone areas. It’s still important to make sure your loft is properly ventilated though, so that it doesn't cause issues with damp - check our advice on choosing an installer, below, for more detail.
However, spray foam is more expensive than other traditional types of insulation, and you’ll need to get a specialist installer to fit it.
As every home is different, and it's hard to remove spray foam that has been installed, we'd advise getting specialist advice from an expert in this area before proceeding - read more below in our section on 'finding a spray foam installation installer'.
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. 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.
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 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.
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 as it blocks and reduces airflow. It allows moisture through it so there’s less worry of condensation building up.
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.