Construction Survey
Level transfer — one datum, carried through the whole building
Every floor levelled from the same ground-level reference, not from the slab below. It is what keeps floor levels, thresholds, drainage falls and lift openings agreeing with the drawing all the way up.
On site this work is usually called floor level marking or datum shifting. It is the same job.
What you get
Agreed in the quotation before we mobilise. Level transfer normally delivers:
- A permanent datum mark on every floor, labelled with its level
- Marks positioned to survive the build, not placed where it was convenient on the day
- Closed transfer — measured twice by independent routes, with the agreement recorded
- Slab level survey showing the actual cast level against design, where included
- Level schedule for each floor in CSV or Excel
- Report stating the method used, the closure achieved and any slab outside tolerance
- The original site benchmark maintained and re-checked through the project
Why not measure up from the floor below?
Because errors add up, and they only add up in one direction.
Measuring floor-to-floor means every slab inherits every error beneath it. A few millimetres per floor sounds harmless. Six floors later it is a threshold that does not meet a corridor, a lift opening that has to be cut, or a wet area that drains the wrong way.
It also assumes the slab you are measuring from is itself flat and at its designed level. After a pour, it rarely is exactly. So you are measuring a correct distance from an incorrect starting point, and repeating that all the way up.
Transferring from one ground-level datum each time means no floor depends on the accuracy of any other. It costs a little more per floor and it is the difference between a building that works at finishing stage and one that needs adjusting.
Every transfer is closed before it is used
Depending on the building, the level goes up by steel tape through a shaft or opening — corrected for tension and temperature, because a long tape under its own weight does not read true — or by total station where the geometry allows a direct measurement.
Whichever method suits, the transfer is closed: measured twice by independent routes, and the two results compared before the new level is marked and released for use.
An unchecked transfer is worth very little. It might be right. Nobody can tell, and the whole floor is then built on it.
What depends on getting this right
Level transfer is invisible until it is wrong, and then it is expensive in places that seem unrelated to survey work:
- Finished floor levels — thresholds meeting corridors and landings
- Drainage falls — wet areas, balconies and terraces that actually run to the outlet
- Lift shafts — opening levels a lift installer will not accept if they are out
- Services — invert levels and clearances through the building
- Facade and cladding — floor-to-floor heights fabricated off site
- Staircases — riser heights, which have to divide evenly into the real floor-to-floor distance
Staircases are the one that catches people out. If the actual floor-to-floor height is 30 mm off, the risers no longer divide evenly, and either every step is slightly wrong or one is noticeably so.
Accuracy you can expect
| Measurement | Accuracy | Notes |
|---|---|---|
| Auto level, closed run | ±5–10 mm | Benchmark transfer and levels across a floor |
| Vertical transfer between floors | Closed and reported | Measured twice by independent routes |
| Total station trigonometric level | ±15–20 mm | Where a shaft or opening is not available |
| Slab level survey | ±5–10 mm | Actual cast level against design, across the floor |
Figures are typical achievable tolerances for survey-grade equipment under reasonable field conditions, not a contractual guarantee. The tolerance your structure requires is set by your engineer and the relevant code — tell us the figure you work to and we will confirm our method meets it before you appoint us.
When you need this
- At the start of the project, to establish the site datum
- On every new slab, before floor levels are set
- Before screeding, so falls and finished levels are set from a checked reference
- Before a lift installation, which will not tolerate an approximate shaft
- Before facade or cladding fabrication, which is made to measured heights
- When something at finishing stage does not fit and you need to know which level is wrong
Typical applications
- Multi-storey framesDatum carried to every slab as the structure rises
- Lift shafts and coresOpening levels set to a tolerance the installer will accept
- Wet areas and terracesFalls confirmed before screeding, so they drain as designed
- Basements and podiumsDatum carried down as well as up, from the same reference
- Facade and claddingReal floor-to-floor heights measured before elements are fabricated
- Investigating a mismatchActual slab levels measured to find which floor is out and by how much
Related reading
Levels are taken by auto level or total station, never from satellites — and it is worth knowing why a satellite height is not a level at all until it has been converted.
- Why satellite levels are not sea levels
- Total station or DGPS — how we choose the method
- GPS vs DGPS — the differential principle
Related services
- Grid Setting Out — the horizontal counterpart of this work
- Column Marking — columns set out on each levelled floor
- Foundation Marking — founding levels from the same datum
- As-Built Survey — recording the levels actually achieved
- Construction Monitoring — settlement and movement over time
- All construction survey services
How we work
How we transfer a level
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Establish the site datum
A benchmark brought onto site by closed level run and marked permanently, positioned where construction will not disturb it.
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Re-check the benchmark
The site datum verified again at each visit, because everything in the building is measured from it and a disturbed benchmark quietly corrupts everything after it.
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Carry the level up
By taped transfer through a shaft or opening with tension and temperature correction, or by total station where the geometry allows.
-
Close the transfer
The same level measured twice by independent routes and the two compared. A transfer that does not agree is repeated, not averaged.
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Mark and label
A permanent datum mark set on the slab or a column, labelled with its level, placed where it will still be there in six months.
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Survey the slab
Where included, actual cast levels measured across the floor and reported against design, before the next floor is set out on top.
Questions
Level transfer FAQs
Yes. Level transfer, floor level marking and datum shifting all describe the same work — carrying an agreed level from one place to another so everyone on site is working from the same reference. Site teams use different names for it. Ask for whichever term you are used to; we will know what you mean.
Because errors add up. Measuring floor-to-floor means each slab inherits every error beneath it, and a few millimetres per floor becomes a visible problem by the sixth. It also assumes the slab you are measuring from is itself flat and at its designed level, which after a pour it rarely is exactly. Transferring from one ground-level datum each time means no floor depends on the accuracy of another.
By steel tape through a shaft or opening where one is available, corrected for tension and temperature, or by total station where the geometry allows a direct measurement. Whichever method suits the building, the transfer is closed — measured twice by independent routes so the two agree — before the new level is marked and used. An unchecked transfer is worth very little.
A permanent datum mark on the slab or a column, clearly labelled with its level, positioned where it will survive the build rather than somewhere convenient on the day. Your site engineer works from that mark for finished floor levels, thresholds, drainage falls and openings, without needing us back for every routine check.
We measure the actual level across the slab and report the difference from design, including how much it varies from one end to the other. Whether that is absorbed in the screed, corrected, or accepted is a decision for your engineer. What matters is knowing the real number before the next floor is set out on top of it, rather than discovering it at finishing stage.
Yes. A level survey across a finished slab shows whether it is within tolerance, where the high and low points are, and whether wet-area falls actually run to the outlet. It is worth doing before screeding and tiling, because a floor that does not drain is far cheaper to fix at that stage than after the tiles are down.