As-built survey

What an as-built survey is

An as-built survey shows the real position of the completed works: exactly where the building is, at what height, and where the pipes and cables run. It is compared with the approved design and forms part of the documents when construction is completed.

For underground utilities (water, sewers, cables) the survey must be done before the trench is backfilled; afterwards it is difficult or impossible.

When you need it

• When a building is commissioned.
• When water mains, sewers, gas pipes or cables are laid.
• For a adding the building to the cadastre after construction.
• When the investor wants an independent check of the works.

Documents required

• the approved design (to compare what was built with what was designed);
• a construction permit;
• for utilities: the design and route data.

What an as-built survey contains

• the outline and position of the building relative to the plot boundaries;
• the finished floor level and key heights;
• the routes, depths and diameters of the underground utilities laid;
• manholes, inspection chambers and connection points;
• a comparison with the approved design, if requested.

Common mistakes

The most common mistake is backfilling the trench before the utility line has been surveyed. The route can then only be estimated, and during future repairs nobody knows exactly where the pipe or cable runs. The second most common mistake is ordering the survey only when the documents are filed, when the works can no longer be checked.

What an as-built survey contains

• the outline and position of the building relative to the plot boundaries;
• the finished floor level and key heights;
• the routes, depths and diameters of the underground utilities laid;
• manholes, inspection chambers and connection points;
• a comparison with the approved design, if requested.

Common mistakes

The most common mistake is backfilling the trench before the utility line has been surveyed. The route can then only be estimated, and during future repairs nobody knows exactly where the pipe or cable runs. The second most common mistake is ordering the survey only when the documents are filed, when the works can no longer be checked.