From IFC to Lesosai in Minutes: BIM-Based SIA 380/1 and Minergie Workflows

Lesosai is the standard tool for building energy balance and certification calculations in Switzerland — SIA 380/1, Minergie, CECB-related workflows. Yet in most offices, the geometry input still happens the pre-BIM way: someone sits with the plans and measures envelope surfaces, window areas, and orientations by hand, then types them into the software.

This is slow, error-prone, and it gets worse over the project's life. Every façade revision, every changed window, every updated floor plan means re-measuring and re-typing. And when the certification result is challenged, the manual takeoff is the first place errors hide — with no traceable link back to the architect's model.

The irony: the architect already has all of this geometry in their BIM model. The problem is that a raw architectural IFC is not structured for energy calculation — spaces are missing or leaky, envelope surfaces are not cleanly bounded, and the thermal zoning logic does not exist. That gap is exactly what automated normalization closes.

Technical Step-by-Step: The IFC-to-Lesosai Normalization Protocol

This workflow works with IFC files from ArchiCAD, Revit, Vectorworks, or SketchUp. The only prerequisite is that the model contains IfcSpaces (room volumes).

1. Request the Right Input (Phase 1): Ask the architect for an IFC that contains IfcSpaces, ideally modeled from top of finished floor to bottom of structural ceiling, plus windows and doors. That is the entire requirement — no modeling guideline, no 300-page BIM manual, no back-and-forth about layer structures.
2. Verify the Spaces Exist (Phase 2): Open the file in a free IFC viewer and confirm room volumes, windows, and doors are present. If spaces are missing, one sentence solves it: "Please export with IfcSpaces enabled." Every major authoring tool supports this natively.
3. Upload to abstractBIM (Phase 3): Upload the IFC at abstractbim.com. The engine rebuilds the geometry from the IfcSpaces: it seals the envelope, resolves overlaps and gaps, computes consistent space boundaries, and knows for every wall which spaces — or which space and the exterior — it separates. Exactly the information an energy balance needs.
4. Download the gbXML Export (Phase 4): Download the normalized model as gbXML. The export carries clean zone volumes, envelope surfaces with orientations, and window openings — the geometric backbone of a SIA 380/1 calculation.
5. Import into Lesosai and Assign Physics (Phase 5): Import the gbXML into Lesosai. The geometry arrives structured, so your work starts where your expertise actually matters: assigning constructions and U-values, defining thermal zones and usage profiles, and running the SIA 380/1 or Minergie calculation.
6. Repeat on Every Design Iteration (Phase 6): When the design changes, upload the new IFC and re-import. The geometry stays consistent and traceable to the architect's model — which also makes the certification calculation defensible when questioned.

Comparison of Geometry Input Strategies