The subject of spray foam insulation recently made it to the 6 pm BBC News, and is something we occasionally come across in roof spaces, where it has been applied to the underside of the roof. Most commonly this is done to improve thermal insulation.
It has been around for many years and I first recall seeing it in the 1980’s.
Typically, in the early days it was regarded as a temporary method of extending the life of an unlined slate or clay tile roof covering that would otherwise require early renewal and was sometimes used as a short term fix, prior to a planned renewal.
The problem has always been that many domestic mortgage lending sources do not accept property with spray foam and will require that it be removed prior to advance of mortgage monies.
Official concern is that where timbers are encapsulated by insulation, moisture either from roof leaks or condensation will be trapped, causing premature decay of the timbers and shortening the life of the roof, which might fail during a typical 25 year mortgage term.
There is plenty of evidence that this occurs where foam has been in place for many years, and I have even seen fungal growth growing through the foam at ridge level in a cottage, indicating where concealed decay of roof timbers was occurring.
Neither a ‘warm roof’ or cold roof – this will result in condensation and increased risk of decay
Encapsulated timbers are at risk of condensation and eventual decay
Where spray foam is present, it can seriously impact the saleability and value, until removed. Removal costs can be high and often require complete renewal of the roof covering and any decayed timbers.
Whilst older spray foams were closed cell, newer breathable spray foams are now available. These are much softer and easier to remove but still represent a risk to the roof structure where timbers are encapsulated without appropriate ventilation or vapour barriers.
In all cases, removal tends to be costly and can cause damage the underfelt, leaving the roof vulnerable to leaks.
The discovery of spray foam causes delays and unexpected costs on resale or remortgage which usually results in the sale or remortgage stalling.
The RICS published a Consumer Guide to Spray Foam Insulation in 2023 and a copy of this can be accessed via the following link:
If you are still tempted to install spray foam insulation, it is essential that you first obtain independent professional advice on its correct installation, to ensure that appropriate linings, vapour barriers and ventilation are put in place. You must also obtain written consent from your mortgage lender that the proposed works are acceptable.
