Fire Safety Considerations for Modular Timber Construction 

 

In recent years, an increased global drive for sustainable development, along with housing availability challenges in many regions, has led to increased interest in the use of structural timber elements. This has been accompanied by an increased appetite for the aesthetic benefits of exposed timber.

The combustibility of timber presents challenges for its use in these structural applications and requires greater understanding of the effects of exposed timber on fire behaviour. Fire safety concerns are a major contributor to regulatory limitations upon the use of timber and other combustible building products. Despite the current uncertainties, the increased attention on timber use represents an opportunity to expand the existing fundamental fire science to ensure that future structures can be designed to be sustainable and safe.

Several decades of research has been conducted regarding the fire behaviour and flammability parameters of natural timber. However, efforts to understand the burning behaviour and fire performance of engineered timber products began relatively recently. As a result, several important knowledge gaps remain and there is a lack of consensus regarding the fire performance of buildings constructed from engineered timber products.

This is particularly true where timber structural elements and/or exposed timber elements are included within a buildings design, and for tall timber buildings in which evacuation requirements are intensified.

The combustible nature of timber presents challenges to guidance cited by existing building regulations and their suggested routes to compliance – which are built upon the assumption that the building’s structure does not contribute to the fire.

The full report summarises these continuing knowledge gaps and discusses the implications for timber modular construction (of various heights) with a particular focus on the challenges and issues raised within the existing regulatory framework.


Conclusion

The current demand for timber based construction looks set to continue, with greater use in tall timber buildings and modular construction likely. Fire safety concerns will continue to exert an influence on the regulatory environment and pose challenges for more complex building projects. Approaches to these constraints will vary, with many practitioners content to satisfy the existing building regulations through standard approaches outlined in supporting technical guidance, despite the very different context in which these approaches were developed.

The inclusion of combustible structural elements and/or exposed combustible compartment  boundaries challenges our existing concepts of fire resistance developed for non- combustible elements. This framework explicitly incorporates the notion of a ‘design for burnout’ which, for non-combustible elements, ensures required functionality remains until the fuel load within a building has ceased burning. Where combustible elements are used, such as engineered wood products, these elements can themselves (unless adequately protected e.g. via encapsulation) contribute to the fuel load, and hence designing for burnout becomes meaningless unless auto-extinction occurs.

By acknowledging the limitations, for combustible timber elements, of a fire resistance framework based upon ‘survival until burnout’, existing and ongoing research efforts can be harnessed to define a design philosophy which from its conception considers the inclusion of combustible elements.

Limitations of the current system are well-documented, and a number of clear research needs are apparent, in order to allow the adequate design of encapsulation systems or compartment layouts that promote auto-extinction and burnout.


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