BIM in existing buildings: opportunities through digital precision

Anyone designing for an existing building rarely starts with a fully reliable basis. Walls have been moved, services added, shafts altered or previous conversions incompletely documented. What looks clear in the as-built drawings may look very different on site. This is one of the greatest challenges in refurbishment and conversion projects: before design can begin, it is necessary to establish as accurately as possible what is actually there.

A key success factor is capturing existing buildings early using 3D laser scanning. The resulting point clouds create a digital representation accurate to the millimetre. This provides far more reliable information than often incomplete or outdated as-built drawings. Only then can construction tolerances, subsequent alterations or unclear service routes be reliably identified. In areas with dense service routing, wall and floor penetrations or facade connections, even the smallest deviations can require extensive redesign. If these problems are only discovered during construction, delays and additional costs are inevitable.

From point cloud to digital twin

The point cloud provides the basis for precise modelling and seamless integration into the BIM process. Investment in 3D scanning pays off twice: it creates design certainty and opens up new ways of using building data, from virtual walkthroughs and digital planned-versus-actual comparisons to predictive maintenance.

At apoprojekt, we go a step further: we involve MEP contractors early and enable them to transfer the clash-checked 3D detailed design directly into their fabrication and installation planning. If coordinated 3D design is subsequently reworked conventionally in 2D, significant efficiency losses arise - for example through time-consuming checks against the design's IFC model, verification of elevations and the resulting susceptibility to errors. Even small changes in one trade can have unforeseen consequences for others.

Sustainability through digital precision

The 3D model also serves as a 'Single Source of Truth' (SSOT): all relevant attributes, from building components to material information, are centrally linked and accessible to everyone involved. This creates transparency, minimises risks and supports sustainable construction.

Accurate records of specified and installed materials enable equally accurate quantity take-offs and robust life-cycle assessments based on product-specific EPDs. Future refurbishment or deconstruction can also be planned more efficiently. When the materials and components actually installed are documented, this information does not have to be collected again from scratch in later life-cycle phases. The digital twin thus becomes a tool for informed decisions.

Existing buildings in particular demonstrate that BIM goes far beyond a three-dimensional building model. Its real value emerges where precise surveys, coordinated design and building data usable over the long term come together.

Developing existing buildings for the future therefore requires, above all, a reliable digital foundation. Combining laser scans with integrated BIM design can make refurbishment, conversion and extension projects more precise, economical and sustainable.