How is building height measured?

According to ACT - Advisory Note 09 – Building Heights, Storeys and Basements, building height is measured as the vertical distance from the datum ground level to the highest point of the building.

The datum ground level is the surveyed ground level used as the reference for measuring height and is typically shown on the field survey submitted with a development application. The height measurement includes the highest part of the building, including rooftop elements such as lift overruns, fixed mechanical plant, and rooftop garden structures. It does not include features such as paving, driveways, roads, surface car parks, fences, courtyard walls, retaining walls, or transportable buildings not intended for long-term habitation.

Reference: ACT - Advisory Note 09 - Building Heights, Storeys and Basements - https://www.planning.act.gov.au/__data/assets/pdf_file/0012/2323002/an09-working-out-building-heights-storeys-basements.pdf