Non-combustible insulation in roofs and balconies
Building Regulation Approved Document B Volume 1 Dwellings requires that balconies on buildings over 18m high are constructed using non-combustible materials as they are classed as part of the external wall. There are some exceptions to this requirement, most notably Regulation 7(3)(g) which exempt ‘membranes’ from the need to be non-combustible (Class A1 or A2-s1, d0 to BS EN 13501-1).
No part of Building Regulation Approved Document B Volume 1 Dwellings requires a roof or roof terrace to be constructed using non-combustible materials, instead it requires the roof assembly to achieve Broof(t4)* to BS EN 13501-5; but there are instances where an insurance company or client are requiring the use of non-combustible insulation in roof assemblies.
The range of flat roof insulation boards classed as non-combustible is limited, consisting of either Cellular Glass or Stone Wool. Both of these generic products have higher Lambda values than XPS, EPS, PIR or VIP combustible insulation boards and will therefore be thicker to achieve given U-value, something that specifiers and main contractors need to be made aware of as early as possible to avoid issues with threshold, upstand and balustrade heights.
All parties also need to be aware that just because the core of an insulation board is non-combustible, the finished product may not achieve that classification. For example, the addition of a facing to the insulation board can change the fire performance, with some products moving from an A1 rating to BS EN 13501-1 to an E rating – that’s the same as most XPS, PIR or VIP based insulants.
Upstand insulation boards are another area where paying attention to what products you use is key. On balconies the upstand insulation board must be non-combustible, but on roofs and roof terrace on dwellings over 18m there are nuances that sales people, estimators, buyers, contracts managers and installers need to be aware of. If your insulation is no more than 150mm above the roof finish it can be made from a combustible material (PIR/XPS/VIP), but any insulation that is against habitable space must be non-combustible (Class A1 or A2-s1,d0). Similarly, any vertical insulation over 150mm high must be non-combustible everywhere.
Whether you are a roofing materials supplier or a roofing contractor, QI are here to help guide you through complying with the Building Regulations on a project by project basis.
* Subject to distance from the boundary as stated in Table 12.1, page 93.
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