Information exchange in existing buildings differs significantly from that in new-build projects. It is therefore essential that all partners in the construction chain work according to the same methodology. The ILS Existing Buildings Working Group is developing new guidelines for information exchange in BIM. These guidelines are now being shared with the market for validation and feedback.

Designing for an existing building requires consideration of heritage values, structural possibilities and constraints, and the technical condition of the property. Because a BIM model functions not only as a design tool but also as a communication tool, it must be practical for all parties involved: consultants, surveyors, and contractors alike. The new ILS for Existing Buildings helps optimize the digital approach to projects involving existing buildings.

Together with SBB Ontwikkelen en Bouwen, a strategy was developed for the construction phase that responded to the tight schedule and the expectations of all parties involved. Before construction began, feedback was gathered from the contractor and co-makers on the architectural principles of the final design. These principles were then incorporated into the 2D detailing and construction sections, aligning the design dossier with the construction process to come.

The BIM strategy was subsequently coordinated in full. The digital information cards developed by SBB played a key role in this process. These cards specify both the architectural information to be included in each element and the geometric representation required for that element across the different phases. SBB coordinated this information with the co-makers, and it formed the basis for the construction process.

To ensure close coordination between all parties, Boltt developed digital mock-ups of various building components, with specific attention to model quality, architectural elements and BIM data. To support the construction process, the model was developed in line with the construction schedule. The longer the lead time for a component, the earlier it was incorporated into the BIM model. This approach was made possible through close consultation and collaboration with SBB.

From the preliminary design onwards, the project was developed as part of a construction team together with contractor Heijmans Woningbouw. In addition to the design work and technical development of the scheme, Boltt played a coordinating role and facilitated the BIM process throughout. The construction team met weekly in Rotterdam, allowing decisions to be taken quickly and the process to move forward with both speed and care.

The detailing was developed in close collaboration with Heijmans Woningbouw and its subcontractors. Because these subcontractors also contributed to the process as part of the construction team, the model and detailing took shape at a relatively early stage. As a result, fewer changes were required later in the process. This led to a key question: could the prefabricated structural elements already be produced during the design phase? In other words, how could the process be organized as efficiently as possible t?

The structural engineer’s archival drawings formed the starting point for the model, while contractor BAM was involved at an early stage in producing 3D as-built surveys and point clouds. This made it possible to verify whether the level data in the point clouds corresponded with the archival drawings. Cross-sections through the point clouds also revealed the extent of the building’s tilt and whether individual components were out of plumb.

To gain a more detailed understanding of the building’s condition, we used high-resolution drone photographs of the full exterior. By comparing these with historical images and archival drawings, we were able to distinguish between original and later elements. This made it possible, for example, to determine that part of the first floor could be demolished. The historical material also helped identify elements that were not shown in the drawings, as well as details that had been replaced over time. One example is the steel windows with opening sections, which were reintroduced in the new design.

BIM was actively used as a communication tool between the contractor, architect, structural engineer and subcontractors. Using the Archicad renovation filter, we were able to clearly distinguish in the 3D model between existing elements, demolition work and new interventions. The same applied to load-bearing and non-load-bearing components, material properties, interior and exterior elements, and NL/SfB codes. The steel supplier also used the model as the basis for sizing its components.