A good example of a durable long-term roof system is two-coat mastic asphalt, providing a waterproofing thickness of 20mm, which is then protected with thermal insulation and stone ballast. Recently, Stubbs Rich specified a mastic-asphalt inverted roof covering an area of 2,800m 2 for the new Begbroke Science Park in Oxford. Benefits of the system include the membrane being maintained at a constant temperature beneath the extruded polystyrene insulation, which also offers protection from mechanical damage by follow-on trades during the construction period. The anticipated life expectancy is in excess of 30 years.The roofing works were carried out by the Oxford Asphalt Company, which has provided roof coverings, tanking systems and asphalt paving for Oxford University for more than 65 years.
The asphalt itself was supplied by Permanite Asphalt and delivered to site in hot charged tankers, hoisted to roof level in heated asphalt luggers, then discharged and laid at roof level by mastic asphalt spreaders. Some 340m 2 of two-coat asphalt was laid on each day the hot charge unit was in attendance.
On completion, electronic roof-integrity tests confirmed that there was no leakage or damage through the waterproofing, which could then be overlaid with extruded polystyrene insulation, shingle and paving slabs.