Will Wigfield from ROCKWOOL UK explains why above ground level amenities such as roofs, balconies and terraces need greater consideration to mitigate fire risk
Fire safety is critical in any home but has a particular significance and complexity when it comes to high rise residential structures.
With limited land to house our growing population, building up rather than out is a logical way to provide a suitable quantity and quality of affordable homes amidst the space constraints of urban life. Yet designing, building and maintaining high rise homes needs careful consideration; especially as outdoor living spaces become increasingly commonplace.
While balconies and roof upstands of ‘relevant’ buildings fall within the scope of the combustible ban, meaning they must be constructed of materials rated Euroclass A2-s1, d0 or better, neither mid-level flat roofs nor terraces count as “specified attachments” in Approved Document B (ADB), and therefore are not subject to the same heightened fire safety requirements.
Heightened risks
It is important to note however, that if a mid-level flat roof system with combustible insulation becomes engaged in a fully developed fire, there could be dangerous consequences. Not only could the combustible material act as a fuel source to potentially attack the facade above, it may also produce smoke and toxic gases that could enter the building through vents or open windows.
This potential is further exacerbated by the range of risks that come with flat roofs. Hot work, for example, is any process that generates flames, sparks or heat and is responsible for 20% of construction site fires and 15% of all fires in commercial and industrial properties.
Hot work can pose a fire hazard to flat roofs during construction, maintenance or refurbishment, with common processes identified by the Health and Safety Executive as posing a significant risk.
Flat roofs also often house mechanical and electrical equipment, the failure of which can result in fire. Equally, as more high rise developments are featuring rooftop terraces and communal gardens, there’s an increase in risk of fire from human activity, whether accidental or malicious.
Moreover, as with external walls, there is the risk of fire spreading to the roof from elsewhere inside the building. But unless it performs the role of a floor, or features an escape route, a flat roof does not count as an “element of structure” and ADB does not provide guidance on appropriate, minimum levels of fire resistance from the underside.
Going beyond
Beyond applications impacted by the combustible ban, ADB places a restriction on the combustibility of materials that can be carried over the roof deck in areas 1,500mm either side of a compartment wall. Where this restriction applies, insulation should be Euroclass A2-s3,d2 or better.
However, non-combustible insulation is increasingly used across the entire roof area of buildings, removing any need to design, specify and install individual zones of non-combustible insulation at compartment wall locations. The use of non-combustible rather than combustible insulation reduces the fuel load available to a fire, and avoids the complication of potentially having to use different insulation materials across multiple zones on the same roof.
As non-combustible materials do not contribute to the spread of fire or emit significant toxic smoke or gases, the installation of non-combustible insulation in a flat roof build-up can be considered best practice. Installing non-combustible insulation across a flat roof matches the established principle of using non-combustible materials in the most safety-critical elements of building construction – and brings the roof, which is in a sense the ‘fifth facade’ – in line with the approach mandated for external walls covered by the combustible cladding ban.
Long-term performance
As well as contributing to the fire safety and thermal performance of flat roof build-ups and facade elements, certain insulation solutions can also deliver acoustic performance which improves conditions for residents.
Third-party accreditations help simplify routes to compliance, clearly demonstrating a product’s suitability for applications such as flat roofs and amenities – and where fire safety is paramount, such as in high rise developments, these clear indicators of quality are extremely valuable.
To help develop industry knowledge on flat roofs and managing fire risk, ROCKWOOL has prepared a whitepaper, ‘Flat roofs: Managing fire risk in
the fifth facade’, and a complementary CPD module. To access, visit
rockwool.link/hmam
Will Wigfield is product manager of ROCKWOOL UK