Description

This is the final report of research into fire spread from lower roofs. This project is part of the larger BRANZ medium-density housing (MDH) research programme.

Increasing demand for New Zealand housing is driving a push towards higher-density housing in urban areas. Increased housing density with larger buildings closer together can potentially increase fire risk. Rezoning of existing residential areas is creating many situations where larger and taller multi-unit residential buildings are planned alongside existing housing stock.

Historically, the New Zealand Building Code (NZBC) Acceptable Solutions for protection from fire included specific requirements to prevent fire spread to external walls from an adjacent lower roof. Similar requirements were added explicitly in the July 2014 amendment of Verification Method C/VM2 Framework for fire safety. Subsequently, the Ministry for Business, Innovation and Employment (MBIE) has received numerous questions regarding clarification of these requirements.

Fires from roofs are not well understood but can be significant. A fire plume above a roof can be initiated either from a fire below penetrating the roof, ignition within the roof or ignition on the external surface of the roof. In the case of a fire below penetrating the roof, the buoyant plume from the fire below exits through an opening in the roof, which may be caused by failure of roof elements when exposed to the thermal conditions imposed by the fire.