The project I am working on is an existing office building, that will undergo renovation works and will have its entrance hall extended (the extension will be a little more than 1,000 sf).
The renovation works will include (amongst other things) the addition of renewable energy sources, replacement of lighting fixtures, enhancement of the ventilation network, and partial replacement of thermal insulation and roof watertightness.
Internal finishes will not be replaced, and the building will be occupied during the works.

Would BD+C Major Renovation or O+M Existing Buildings be more appropriate in this case?

Thanks in advance for your help.