Also known as spray foam, or spray polyurethane foam (SPF), this is an alternative to traditional building insulation such as fibreglass, wool or mineral fibre rolls. It can be used to insulate your roof, loft, walls and floor – but it is the roof installation that particularly causes problems for UK mortgage lenders.

The foam is applied in a liquid form using powered sprayers, which then expands and turns to a solid coating. This foam has greater insulating properties than many alternatives.

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

Open cell spray foam insulation – this has cells that are not completely encapsulated. This makes the foam a more spongey, softer and more flexible material.
Closed cell spray foam – cells in this form are completely closed. This means air and moisture cannot get inside the foam, and it sets much more rigidly and is more stable.
Spray foam insulation is more expensive than other forms of insulation material. For example, a client of ours paid almost £4,000 to have the foam professionally applied under the roof of her 3 bedroomed detached home in Lincolnshire.

It can also cause health issues, as harmful fumes are given off during installation and could linger afterwards. This can affect those with existing breathing or respiratory complaints, including asthma.