Spray foam insulation has been in use for decades, and was included in the government’s Green Home Grant scheme, that closed in March 2022. Yet, despite this glowing endorsement, it is not suitable for use in every property, even when installed by a reputable installer.
It is just one method of insulating the home, and certainly not the cheapest.
There are two types of spray foam, “open cell” and “closed cell”, referring to the structure and finish of each system. Open cell is less dense and remains soft after setting, supposedly remaining moisture permeable. Its insulation properties are not as effective as closed cell, which sets to a rigid finish and creates a vapour barrier, thus preventing airflow to the roof timbers and trapping in moisture that can cause the timbers to decay.
Incorrectly installed spray foam insulation can result in a number of damp issues including condensation. It can also affect the structure of the roof if the second impermeable membrane is damaged as timbers can become damp but they cannot breathe and are hidden from view. Another issue, when works are required after spray foam has been used, is that none of the existing materials can be reused. This significantly increases the cost of a replacement roof.
Spray foam is applied with a spray gun where it expands into the area to form an insulation layer, typically in roofs, lofts and attics, but also other applications including under suspended floors. The application can be messy in the wrong hands and rogue installers have been known to contaminate water tanks and cover electric fittings.
The substance can be difficult and costly to remove but this may be necessary if it has been applied incorrectly. However, home owners are advised against removing the product themselves, largely because some spray foam is toxic and there is a danger of causing damage to the roof tiles, electrics, water tanks or other items.
Some mortgage lenders will refuse to lend and others may be uneasy about lending on a property with spray foam insulation and it may affect your ability to sell your home, remortgage or release equity release. Spray foam covers the entire inside structure of the roof, which means it is not possible for a surveyor to inspect the condition of the roof timbers or speculate on any risk, which may adversely affect any valuation of the property.
There are currently no controls for installers, and no way of formally determining a reputable firm from a rogue operation. Organisations including the Homeowners Alliance and Property Care Association are working with insurers, mortgage lenders and surveyors to develop a system of installation procedures for installers and inspection protocols for surveyors.
If your home already contains spray foam insulation make sure you keep any paperwork related to its installation, including specifications and independent test certificates issued by organisations such as the British Board of Agrément.
Home owners are advised to get an independent expert to check whether or not spray foam insulation is suitable for their property before instructing an installer. Your local independent Chartered Surveyor may be able to provide you with impartial, professional advice.