An as-built survey documents, by measurement, the real, constructed state of a structure, facility or infrastructure. What is drawn in the design and what is built on site often diverge; the as-built removes this gap by putting it into measured figures.
Why do the design and the site diverge?
No structure comes out exactly the same as its design. There are small but cumulative reasons:
- Site decisions — revisions made during construction are often not fed back into the design.
- Tolerances — every installation and fabrication is done with an acceptable margin of error.
- Later additions — lines, equipment and services change over time.
- Old structures — some facilities have no up-to-date drawings at all.
This divergence creates risk when a new investment or revision is planned: a line designed by trusting the old drawing can clash with the real situation on site.
How is an as-built measured?
An as-built survey is carried out with different methods depending on the scale of the work:
- Total station and digital level — point-based, precise position and height measurement.
- 3D laser scanning — recording the entire facility as a point cloud; the most efficient method in complex, dense environments.
- GNSS — positioning in wide, open areas.
The data collected is turned into 2D as-built drawings, sections or a BIM model. The resulting document is thus based on measured reality rather than assumption.
Where is it needed?
- Factory revision and investment projects — overlaying a new line onto the existing state.
- Structures with no drawings — digitising old facilities and buildings.
- Services and infrastructure — the real routing of mechanical, electrical and process lines.
- Handover documentation — an “as-constructed” record after construction.
Its value: removing guesswork
The return of an as-built survey is that it eliminates uncertainty before a decision. A correct as-built document prevents clashing designs, surprises that emerge on site and the delays that follow. The as-built output prepared within industrial surveying places investment decisions on solid ground.