Sprayed Foam Insulation

As we all try to minimise fuel costs the issue of sprayed foam insulation has again come into focus. Also known as Spray Polyurethane Insulation (SPI) is comes in two forms, open cell and closed cell.

It can be applied to the undersides of a roof and companies are starting to offer it as a means of insulating beneath timber floors.

Insulation of this type is relatively quick and easy to install by a specialist contractor and it can prevent drafts. It is more expensive that traditional insulation but it has good insulating properties with a 100mm thickness equating to around 170mm conventional loft insulation.

The problems occur when a roof leaks. Leaks will be difficult to trace and the insulation can trap moisture leading to timber decay.

We carried out a Survey inspection of an old cottage around 15 years ago which had SPI beneath the roof. The stone roof slates were in poor condition and leaking in many areas. Trapped condensation was also adding to the problems and the extent of timber damage was such that the property required a full new roof. The cost would have been significantly increased as the foam insulation would have required removal. It prevented re-use of the stone slate which is a very expensive material in very short supply. In todays money the repair bill would be in excess of £100,000.

If the roof coverings are in good condition the risks are less but some mortgage companies will decline to lend on a property with SPI fitted. It is also justification for a down-valuation.

We are awaiting further guidance from the RICS and other professional bodies but in the meantime if you are considering sprayed foam insulation we would strongly recommend it be avoided and instead consider conventional mineral fibre loft insulation or better still the insulation made from recycled bottles or sheep’s wool.

In respect of floor insulation the advice is the same. It is very important that floor timbers are exposed to air circulation to protect then from rot and wood-beetle damage. Insulating floors is problematic unless there is access from beneath but the use of sprayed foam would likely cause significant problems, especially in an old house where problems of dampness in the sub-floor void are very common.