The merits of building in non-combustible materials such as masonry are self evident to most. The Department of Communities and Local Government has published data that shows that statistical analysis of fires in timber buildings demonstrates that timber buildings are more susceptible to fire spread. Few would be surprised at this finding. The same report cannot find a statistical relationship between construction type and injury or death. This may in part stem from the very low numbers of injuries and deaths due to fire, which of course is good news in itself, but should not breed complacency.
Designers, developers and clients obligations under CDM legislation
All parties in a project should consider their obligations under CDM legislation which requires them to mitigate risks to safety of occupants. This mitigation in respect of fire is best demonstrated by choosing non-combustible materials, particularly given that the obligation is for the life of the building, and choosing a non-combustible material is the most effective way of mitigating against future modifications and refurbishment works which may compromise fire compartmentation and fire-stopping. The HSE has also issued a public letter relating to construction stage fires.
The table below summarises the different aspects of fire resistance and how masonry performs:
|The ability to continue to carry the loads on the structure
|The ability to act as insulation against the heat from a fire
|The ability to prevent fire spread through the structure
Masonry is more forgiving over the whole lifetime compared with combustible materials because with masonry the requirements are less onerous ( see Fire Details) and the structure will not burn. This relative risk of using combustible materials lay behind the NHBC Foundation publishing “Fire in Cavities in residential buildings: The performance of cavity barriers in external walls with combustible materials”.
There are no special measures required for masonry buildings during construction regarding fire risk, whereas there are extensive measures for timber buildings. Furthermore the HSE is very concerned that these are not being followed and designers should consider mitigating the risk through design.
The HSE issued an open letter to all parties involved in the design, specification, procurement and construction of timber frame structures (29 October 2014). The letter is available on their website which states:
“Evidence from recent HSE inspections indicates that the risk of harm to occupants of neighbouring buildings from fire during the construction phase is not always effectively managed through either of the options above, [following STA’s publication ”Design guide to separating distances during construction” or a competent person] and that not all duty holders understand what is required of them.”
Therefore there is a greater risk from the use of timber construction. It also states:
“All those making design and procurement decisions that significantly affect fire risk should consider and reduce the risk and consequences of fire during the construction phase through DESIGN.” (HSE emphasis)
The masonry industry suggest that whilst proper design is required no matter what structural material is chosen and whilst workmanship is always important, a sensible starting point in risk mitigation is to choose non-combustible structural materials. Masonry is also sustainable: local, responsibly sourced, just as thermally efficient through airtightness and insulation, while providing additional benefits of thermal mass, acoustic resistance and low whole-life carbon. Furthermore masonry solutions are cost effective. There is no reason to take the risk of using a combustible structural material.