Recently I was asked to do a roof survey of a roof in Camden that had spray foam added to the underside of the pitched roof the property was on the market and a Royal institution of chartered surveyors (RICS) property surveyor had just given the customer a survey report, that stated that the spray foam between the joists should be removed because it is blocki
ng the ventilation of the roof and may make the roof unstable. I was asked to go and inspect the roof before the insulation was removed and to make sure that this was the case.
My findings
Looking around the roof, you could definitely see that the phone had been installed between all of the rafters and it was definitely stopping movement of air into the loft space.
I was also able to determine that the foam had been sprayed directly onto the back of the tiles, leaving no gap for movement of air.
Conclusion.
The foam has stopped movement of air to the back of the tiles. This could possibly cause the battens that the tiles are fixed to and the fixings of the tiles to the battens to the rafters to rot prematurely if left for a long time. Structural timbers could also rot.
Findings after the spray foam was removed.
My second inspection of the roof took place approximately two weeks later after all the spray phone had been removed from between the rafters. This revealed that the spray foam had been stored tight up against the tiles without leaving a gap for ventilation.
Deterioration of the battens and some of the structural timbers was observed.
It was also observed that the removal of the foam had damaged the back of some of the tiles. As the roof was already quite old, some of this damage could have already been happening before the installation of the foam. Whatever way you look at this the roof needs to be replaced and the insulation needs to be installed correctly. Probably at ceiling level leaving the loft space as what's known as a cold space.
Generally speaking spray foam pitched roofs is not a good idea and will be condemned by most surveyors.