Fire Safety of Wooden Façades in Residential Suburb Multi-Storey Buildings

The fire classes and numerical criteria given in the regulations and guidelines of part E1 of the National Building Code of Finland (NBCF) specify limitations to the use of wood in the façades of buildings belonging to the fire class P1, but they do not, however, prevent the use of wood. The issue is the way how the essential requirement of safety in case of fire is shown to be satisfied. There are two alternative ways to show this: the other, more common way, is to design and execute the building by applying the fire classes and numerical criteria provided by the regulations and guidelines. The other way is to design and execute the building on the basis of design fire scenarios, which shall cover conditions likely to occur in the relevant building (the performance-based way). In this case, one can employ solutions that differ from the fire classes and numerical criteria given in part E1 of the National NBCF provided that they are proven to be safe. A prerequisite for the use of the alternative fire safety design approach is that there is solid, validated material to base the design on. The objective of this study is to produce such material concerning use of wooden façades in residential multi-storey buildings built according to the requirements of the P1 fire class with non-combustible load-bearing structures. The work that has been carried out as a fire risk analysis concerning the impact on fire safety of an installation of a wooden façade. The risk analysis and associated calculations are made using state-of-the-art techniques in the fire safety sciences and technology. The results obtained show that with respect to the overall fire safety of a P1-class residential multi-storey building, the role of the combustible façade material is insignificant: the minute increment in the probabilities of fire spread from the room-of-fire-origin to the apartments above is small as compared to the influence of several other factors which are not regulated by the Fire Regulations. For example, the small amount of wood on the façade that is likely to contribute the external flaming would cause a much higher risk if it was installed - as allowed by the Fire Regulations - as a lining inside the apartments. It is shown that the results obtained for the selected example building can be generalised to other buildings with reasonably similar characteristics.