Temporary benchmark (TBM)
A temporary benchmark (TBM) is a fixed reference point with a known elevation used to control all height measurements on a construction site throughout the build.
Ask Chalkline about this →A temporary benchmark (TBM) is a fixed point with a known elevation established by a registered surveyor at the start of a project, used as the reference for all height measurements on the site throughout the build. Common physical forms include a nail set in a kerb, a mark on an existing concrete structure, or a steel pin driven into stable ground outside the footprint.
The TBM elevation is tied to either AHD (Australian Height Datum) or an assumed local datum, as specified by the engineer. Every reduced level (RL) on site, including finished floor levels, footing depths, and drainage inverts, is measured relative to the TBM. If the TBM is disturbed by earthworks or plant, the surveyor must re-establish it before any level-dependent work continues. Pouring concrete referenced to a disturbed TBM is a serious error.
Also known as: site benchmark, construction benchmark.
Category: Surveying and levels.
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Last updated: 2026-05-10. Verified: 2026-05-10. Quarterly review for currency.