As you say there are conflicting opinions on spray foam insulation and it is fair to say that the vast majority of loft converters will use foil backed insulation boards. However the manufacturers of spray foam products do claim that outstanding results can be achieved with the material.
It is true that with spray foam there is no need to leave a ventilation gap when the foam is applied directly to the slates or roofing felt and because the material is applied between the rafters there is usually no loss of headroom. Incidentally the rafters and foam insulation can be covered with plasterboard or plaster can be applied straight on to the foam.
It is important to check that any spray foam you consider using is compliant with the energy saving criteria laid down in the building regulations and has a British Class 1 fire rating. Generally spray foam does have good thermal insulation properties and in normal use and shouldn?t create any condensation problems though of course it is always wise to seek assurances from the installer.
