Paul Bayliss MRICS, C.Build E MCABE, FISVA
Chartered Building Surveyor and Chartered Building Engineer.
Dear David
I have followed the developments of this legislation via the various journals published by CABE, whom as Building Engineers and fire risk assessors, ( you might already know) have been influential in this area. My understanding of the culture of the legislation is to adopt a sense of pragmatism, so for me the dimension is taken from the lowest external ground level. That seems eminently practical and logical to me, given the similar approach taken when applying the guidance under Approved Document Part B. Risk is accepted, but guidance presumes a practical application to mitigate.
Not withstanding Pauls very helpful and incisive contribution, I can see a barrister arguing that a roof light / roof well is in fact a “ceiling” where as to most Surveyors, I would argue that it is or only ever would be a part of the “roof” construction to that element. So the light well is subterranean and thus discounted. I may not have explained that point particularly clearly? apologies.
Ultimately you go with what you are most comfortable with of course. Like all new legislation its interpretations will be challenged in years to come, so we can only wait and see.
In good faith I hope that might assist? Just a view nothing more.
Kind Regards
Paul.