Belfast·SPG006 Tall Buildings·Page 8·3.1.4
Height threshold application to extensions and roof-level elements
The 35m AOD threshold includes extensions to existing buildings and additional massing at roof level for plant and lift/stair overruns. Height is measured in metres rather than storeys to account for varying floor-to-ceiling heights across different building uses.
The upper height threshold of 35m AOD will include extensions to existing buildings as well as any additional massing required at roof level to accommodate plant, such as air handling units and lift/stair overruns. This threshold has purposefully been set out in metres as opposed to storey heights given that the latter can vary according to different uses, such as the taller floor to ceiling height requirements normally associated with office development when compared to lower floor to ceiling heights associated with residential uses.
Source — /Users/richardhill/Documents/planning-arch-project/data/documents/belfast/SPG006 Tall Buildings.pdf