Empirically tested
As soon as there is a fundamental intervention in the old building fabric, it becomes virtually impossible to obtain and “exemption” from the planners for the old timber ceiling structure. This applies especially to timber beamed ceilings with a fore resistance class F90B which is the level stipulated for multi-storey buildings. The requirement for timber beams to be in category F90B means that, when exposed to the full force of a fire (1200°C) from above, from below and from the side, a remaining time window for escape of 90 minutes must be guaranteed, before a supporting structure that conforms to the standard may fail. Such a standard level of fire protection therefore faces solution providers with major technical and legal challenges.