Q. We are looking at a property that has had its slate roof under sprayed with polyurethane foam. So much so that you cannot see the roof timbers at all. Will this cause damp at some stage?

Submitted by: PS

A. Whilst the foam on its own will not cause damp the very fact that it is there means something was probably not right before it was applied. This foam is commonly applied when a slate roof starts to suffer from 'nail rot'. This basically means the nails holding the slates in place corrode and the slates start to slip. By applying the foam to the underside it 'sticks' all of the slates in place thus preventing further slip. In so doing it also provides a degree of insulation but this would be better positioned directly over the ceilings rather than under the slates. It probably means that the original roof is 'tired' and may be near to the end of its useful life but the foam has extended its life.