How is building height measured on a sloping block?

Building height on a sloping block is measured from Datum Ground Level (DGL) to the highest point of the building.

ACT Planning’s Advisory Note 09 specifically explains that DGL is the base used for calculating building height. It is determined from an authorised field survey from the time of subdivision or grant of the lease. If that information is unavailable, a registered surveyor determines the best estimate having regard to surrounding ground levels. For a DA, the DGL is normally shown on the field survey submitted with the application.

This means the building height on a sloping site is assessed against the surveyed DGL, rather than simply measuring from the lowest or highest point of the current ground.

Reference: ACT Advisory Note 09 - Building Heights, Storeys and Basements - Building heights, storeys and basements