Spray foam insulation – blessing or curse?

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A professional property survey can flag up a wide range of problems with the building, but were you aware that the presence of spray foam insulation can be an issue of serious concern?

Spray foam insulation has been available in the UK for over 30 years. It’s a liquid foam that is sprayed onto the underside of roof pitches to provide an additional layer of insulation to the property. Spray polyurethane foam (SPF) is often applied to a sloping roof in poor condition, or as a convenient quick fix. In recent years, it has become more popular with homeowners as a viable alternative to traditional loft insulation materials such as fibreglass, wool or insulation boards.

Unfortunately, mortgage lenders are increasingly taking a very dim view of this type of insulation and are reluctant to approve loans for properties with SPF insulation. Many lenders will not approve the loan at all. Surveyors and valuers are therefore having to discount the market value of affected properties, or request a specialist investigation if SPF insulation is found to be present.

Why use spray foam insulation?

SPF is applied as a lightweight liquid foam that sets and hardens in situ after application. It is typically sprayed as a 100mm thick layer onto the underside of the roof, and the installation may release lingering toxic fumes. The material is not a pleasing sight and cannot be decorated over, and it is also more expensive than traditional types of insulation.

On the upside, SPF is a better insulator than mineral wool loft insulation, meaning a thinner layer of SPF is required to achieve the same insulating effect. And as it is applied to the roof slope, it doesn’t get in the way of boarding the floor of the loft space.

SPF contractors are keen to stress the benefits of an installation as a long-term energy-saving investment into the property, promising to save up to 20% on energy bills, protect water tanks and pipes from freezing and keep the loft space dry. In addition, the rigid foam is said to stop roof tiles from slipping and give extra strength to the roof structure.

Two types of SPF insulation are available: open cell and closed cell. Closed cell SPF is firm to the touch and dries rigid, stopping moisture from passing through it. By comparison, open-cell SPF is spongy when pressed and is less efficient as an insulator. However, it does have good sound-absorbing properties and will allow water vapour to pass through it.

What is the problem with spray foam insulation?

The main issue with SPF insulation is that it blocks ventilation in the roof space, which can lead to severe condensation problems. The effect is compounded with closed cell SPF, but even the open cell ‘breathable’ type can still cause condensation in places where foam and roof covering materials meet.

The moisture build-up over time can cause wood rot in the roof timbers. What’s more, defects in the roof covering itself may be concealed from view resulting in water penetration which also leads to timber decay. Damp issues in a roof can be the cause of penetration or condensation – a building survey should be carried out to establish the exact cause.

It is also worth pointing out that spray foam insulation should never be used in a period home or a listed building that often has a stone flag, slate or handmade clay tile roofs. Some of the material is often reusable when the old roof is recovered, however, this is impossible in cases where SPF insulation was applied.

What do mortgage lenders think?

Lender guidance for surveyors regarding spray foam insulation varies, ranging from requests for a structural engineer or roofing contractor report to lowering the valuation on account of the potential cost of roof renewal, to declining the loan outright. For property surveyors and valuers who encounter SPF when carrying out a survey or mortgage valuation, the latest guidance notes for the specific lenders must be front of mind.

Not all mainstream lenders have stated a clear policy on their lending criteria for properties with SPF insulation. If you currently have a mortgage and are considering having spray foam insulation installed, or if you are thinking of purchasing a property with SPF insulation in situ, you should check with your mortgage provider as soon as possible.

At Squarepoint Surveyors in London, we specialise in providing professional building advice to a wide range of clients and properties. For expert assistance and advice on any building surveying issue including party wall surveys, please get in touch with us for a no-obligation consultation.

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