How does the NHBC Chapter 7.1 update affect roof insulation?

As the largest insurer of new construction housing the NHBC plays an important role in the construction industry, producing its own guidance that follows regulations and standards and clarifies their requirements as an insurer. Chapter 7.1 of their guidance relates to roofing and can be accessed free online at:
https://nhbc-standards.co.uk/7-roofs/7-1-flat-roofs-and-balconies/.

Whilst the industry awaits a clarification on a grey area in Approved Document B related to the use of insulation on vertical upstands that abut habitable space and external walls such as parapet walls, the NHBC have provided guidance that may point to the likely direction of travel within MHCLG, who produce the Building Regulations on behalf of Government. 

NHBC have clarified their requirement for insulation used as a thermal break where a roof, balcony or terrace abuts an external wall.  They state that the insulation does not need to be non-combustible as long as the insulation
is not:

• against habited space

• higher than 150mm above the finished roof level/walking surface

• thicker than 60mm

• crossing a compartment line

It therefore would follow that if the vertical insulation is higher, thicker, against habited space or crossing a compartment line it must be non-combustible. It would also be safe to assume that it should run vertically
from the deck with the horizontal insulation butting up to it rather than
being below it as is traditional in a warm roof.

Technical Extra 26 further clarifies the effects of the ban on combustible materials in buildings over 18m in England. This includes clarifying Stepped Terraces, Access Terraces and Podiums are not specified attachments and are treated as roofs; requiring Broof(t4) fire performance. Therefore, it reinforces the point that balconies must be constructed using non-combustible insulation, reinforcing the adage ‘if it’s over heated space it’s a roof, if it’s over air it’s a balcony’.

Unfortunately, this still leaves a conflict between the Building Regulations and British Standards as BS 8579:2020 refers to non-combustible requirements being for balconies on buildings over 11m rather than 18m; perhaps another example of the direction of travel for the awaited outcome of the consultation on Regulation 7…

Next month: BBA Building Bulletin 4, what is it and what’s changed?