As-built surveys are essential to verify a building’s metric and geometric data during and after its construction. Let’s see in detail what it is!
If you deal with construction, you know that one of the essential tasks in the design process is the survey of the building (as-built survey). Basically, it is the measurement of the building after its construction, along with its and graphic rendering .
A survey has many important purposes and, depending on the objective, it is advisable to choose the relevant type of representation and the adequate tool.
In addition, it is essential to use a 3D architectural design software to process the collected data and automatically obtain the BIM model and the drawings (floor plans, elevation views, cross-sections) of the current state.
This article provides some useful information for your as-built surveying activity.
What is an as-built survey?
An as-built survey is the set of geometric surveys conducted on a building during and after its construction. Its aim is to produce drawings (with 2D and 3D models) that exhaustively describe the consistency of the building at that precise moment. The survey is also used to verify the conformity between the approved project and what has actually been constructed.
At the end of the verification survey, the as-built model is created. It is then completed and delivered to the client after the construction of the work (but updated as the work proceeds). The result is an information container that combines the 3D model with the data (geometric and not) related to the completed building (technical data sheets, manuals, photographic documentation, etc.).
In general, an as-built model shows the exact position of the structural, mechanical, hydraulic, electrical and architectural elements to reconstruct a complete picture of the building as is at the time of the survey.
The process of creating an as-built model starts with the geometric survey of the building and the collection of information to be included in the model and ends with the delivery of the BIM model to the client. Essentially, it is the reverse engineering of what usually happens in a traditional BIM workflow in which the 3D model is made to describe the project in detail and support the works to be carried out.
To obtain the 3D as-built model 2 paths can be followed:
- modify the project’s BIM model according to the works actually carried out on site;
- proceed with the acquisition of the geometry of the existing building with special survey tools and techniques (laser scanner, photogrammetry, etc.).
The survey can be carried out with different instruments, from traditional and manual tools, such as measuring tapes, to the most technologically advanced devices (total stations, laser scanners, drones, geoslam, etc.).
The most up-to-date tools certainly return more reliable results, allowing more data processing, time and resources optimization. Large-scale constructions, that are difficult to detect with direct methods, can also be scanned. The result of the survey is the export of a 3D model from which it is also possible to generate floor plans, sections and elevation views of the building. The advantage also lies in a representation that is much more faithful to reality and that also takes into account any inclinations of the walls, static anomalies of the floors, deformations, construction irregularities, etc.
Today, new technologies allow you to combine metric, photographic, thermographic, etc. information and to work directly on a 3D model that highlights shapes, dimensions, materials, critical situations (injuries, deformations, etc.).
All to the benefit of a design of the highest quality level.
Some particluar cases, such as the relief aimed at restoration interventions on the historic building, require a deeper measurement of the decorative elements and the graphics of finishes, materials, state of degradation and construction techniques. In this instance, the most innovative tools are of great help because they allow you to scan every detail of the building, even the most complex.
Nevertheless, as-built surveys are the starting point for all design interventions and the greater its degree of accuracy, the lower the risk of incurring errors and unforeseen events during the construction phase.
The survey phase is followed by the return of the data collected through the processing of 3D models and 2D drawings that represent the surveyed situation.
To know all about as-built survey, I also recommend that you read “Scan to BIM, from laser scanner surveys to the BIM model”.
Why carrying out as-built surveys for the construction project?
Carrying out as-built surveys is essential for the creation of the building’s 3D model.
These operations allow designers to:
- have a precise and reliable model of the work for future renovation, expansion, and maintenance projects;
- have a detailed model for future uses, including the asset’s management phase;
- draw up a maintenance plan;
- carry out accurate energy or structural analyses;
- estimate the costs of the interventions;
- draw up building practices;
- implement the documentation relating to the surveyed situation;
- provide detailed information on the site layout;
- have a template for viewing existing conditions;
- create a BIM model that is the digital twin of the existing building;
- verify the correspondence between the work carried out and that planned in the project.
To conclude, as-built surveys are essential they provide the basis for any future design development.