Conversion of roof space in existing two storey dwellinghouse

Where the roof space of an existing two storey dwellinghouse is to be converted to form a new storey the provisions of this Section are for the floors, both old and new, to have full 30 minutes fire resistance. However, the existing first floor construction need not be upgraded where it separates only rooms (and not circulation spaces) provided that – (a) only one storey is being added; (b) the new storey contains not more than two habitable rooms; (c) the total area of the new storey is not more than 50 m2; (d) it has at least modified 30 minutes fire resistance; and (e) the provisions of paragraphs 2.17 to 2.22 are met.