All work is guaranteed and the insulation is maintenance free for the life of the roof. Websters Insulation are an approved installer of Duratherm which holds BBA Accreditation No. 10/4771 in respect to the materials manufacturer Isothane Ltd. Duratherm is recommended for spraying under tiles / slates, under-felt and breather membranes. It meets building regulations and seals your roof from draughts and wind driven rain all in one application.