Benchmark (repère altimétrique): what the project manager needs to know about this surveyor’s reference point to avoid building misaligned floors and finding out only when the joinery goes in
“The surveyor has set the benchmark at the entrance to the plot. This benchmark lets the contractor precisely set the floor-level heights.” A poorly placed or damaged benchmark, and every level in the building is wrong.
Type | Phase | Actors | Impact | Stakes | Where |
|---|---|---|---|---|---|
Technical | Execution | géomètre, MOE (project manager), Architect, Contractor | High | contractual | Foundations or Setting-out section of the CR |
1. Operational definition + common mistake
The repère altimétrique (elevation benchmark) is a reference elevation physically marked on site by the surveyor, from which every vertical measurement (height) in the building is measured and set out. It’s usually tied to the French national leveling network (NGF) or a local elevation defined in the building permit. On this project, it was marked “at the high point of the access ramp at the entrance to the plot” and communicated to the architect, the MOE, and the contractor.
This benchmark directly determines: the levels of each floor slab, ceiling heights, opening heights, connections with external utility networks, and compliance with the building permit.
Many assume the benchmark is “the surveyor’s job” and that once it’s set, the matter is closed — in reality, the benchmark must be preserved throughout the project. If it’s destroyed, the contractor loses their reference point and can set incorrect levels. The MOE must ensure it’s protected and document its position in the CR.
2. Where it appears
In a site meeting report — in the Foundations, Setting-out, or Surveyor section, during the early phases before foundations and masonry. In this CR:
“The surveyor has set the elevation benchmark at the entrance to the plot, at the high point of the access ramp. This benchmark has been physically marked on site and the corresponding drawings have been sent to the architect, the project manager, and the contractor GDR.”
“These elements let GDR precisely set the floor-level heights for the house.”
3. How to read this entry in the CR
If you read “elevation benchmark marked” → ask the surveyor for the corresponding drawing or elevation note; archive it. Check at every visit that the benchmark is still visible and protected.
If you read “benchmark communicated to the contractor” with no confirmation → check that the contractor actually received the document and knows where the benchmark is on site.
If the benchmark is destroyed or can’t be found → stop all leveling work and call the surveyor back before resuming.
4. Who does what
Actor | What the benchmark means to them | Concrete action |
|---|---|---|
Surveyor | A reference point to create and document | Physically mark the benchmark on site; send the leveling drawing to the architect, the MOE, and the contractor |
General contractor | The reference for all their level measurements | Use this benchmark exclusively; physically protect it |
MOE / architect | A reference to check and preserve | Check the benchmark’s presence and condition at every visit; alert if damaged |
Client (MO) | Informational | Be aware of the reference elevation |
5. What this changes in practice
A project manager who documents the benchmark in the CR and checks its presence at every visit can guarantee the building’s vertical consistency. A project manager who never mentions the benchmark in their CRs risks discovering, when joinery or tiling is installed, that the levels are off.
Failure scenario: the elevation benchmark is destroyed during excavation for the drainage system. Nobody notices. The contractor re-establishes their levels by eye. At the end of the shell-and-structure phase, it’s discovered the upper floor slab is 12 cm too low. Replacing every lintel to recover the ceiling height costs €18,000.
6. Example of real wording
“The surveyor has set the elevation benchmark at the entrance to the plot, at the high point of the access ramp. This benchmark has been physically marked on site and the corresponding drawings have been sent to the architect, the project manager, and the contractor.”
7. Points of caution
A destroyed elevation benchmark can only be re-established by the surveyor: never let the contractor “work it out” on their own.
The benchmark must be physically protected on site: flag this to the contractor in the site instructions.
The benchmark’s elevation must be checked against the building permit and the national leveling network (NGF) where applicable.
A single benchmark may not be enough on a large plot: check with the surveyor whether secondary benchmarks are needed.
The surveyor’s leveling drawing must be included in the as-built file (DOE): it’s part of the “as built” documents.
8. Not to be confused with
Related term | Key difference |
|---|---|
Setting-out drawing | A surveyor’s document locating the building horizontally — the elevation benchmark gives the vertical reference |
NGF | The national elevation reference network — the site benchmark may be tied to it |
Finished floor level | The resulting construction elevation — the benchmark is the reference from which this elevation is measured |
Boundary survey (bornage) | Legal delineation of the property — a distinct surveying operation from leveling |
9. Related terms
Same phase (foundations/setting-out): Setting-out · Surveyor · Ground beams · Foundations · NGF
Same actor (surveyor/MOE): Site plan · DOE · Building permit · Leveling
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