Are they recognised by the National House Building Council?

Provided they have been constructed in accordance with the NHBC Standards (Chapter 7.1) then yes, green roofs are recognised by NHBC. In practice they are
looking for the Green Roof system to be designed and supplied by the roof membrane manufacturer to ensure that one company takes responsibility for the green roof and waterproofing element. They also require that the system (including the waterproofing layer) is installed by the manufacturer’s approved installers.