A Proportionate Reaction to Fire Risk: Refurbishment & New Build Flat Roofing Specification Design

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Cameron Payne - Flat Roof Technical Manager

Fire is a risk that must be considered in every roof design and specification. But our reaction to dealing with the level of risk should be both measured and proportionate.

The minimum requirements set out in Approved Document B must be met, that much is clear. But there is compelling expert opinion that there has been a disproportionate reaction in some areas of the construction market, creating unnecessary anxiety, adding costs, and increasing complexity where there is no need.

The Independent Review of Building Regulations and Fire Safety, Chaired by Dame Judith Hackitt, led to the following statement: “there has been an overreaction and excessive risk aversion in some parts of the market, which is leading to interventions that create excessive financial burdens disproportionate to the level of risk”. The statement was featured in the ‘Independent expert statement in building safety in medium and lower-rise blocks of flats’ published 21 July 2021.

Although the focus of the independent review and statement may have appeared to be on the external walls and façade, the review addressed the entire building envelope, including flat roofs. Considering this, combined with the expert statement quoted above, the roof design must be carefully considered to encompass mitigation of fire risk as well as accommodating other design requirements.

Insulation materials such as mineral wool have obvious benefits in relation to their fire performance, being non-combustible. But it’s not that straightforward. There are several considerations that specifiers need to be aware of when proposing its use. These can include higher weight loadings, increased costs, limited availability, and inferior thermal performance than other types of insulation. The inferior thermal performance of mineral wool insulation can lead to deeper thicknesses, compounding the factors already mentioned and potentially compromising the roof design.

Combustible materials such as PIR insulation can be used when specified as part of a Broof(t4) rated system (tested to TS 1187 and Classification to BSEN 13501-5:2004) if the building’s use is included in the ‘Special Application Group’ as set out in Approved Document B and the building is not more than 15m high.

To learn more about the requirements of Approved Document B and the considerations to be aware of when specifying your flat roof systems, contact us at to book a CPD.