gbXML (Green Building XML)
The gbXML format for transferring building geometry and HVAC data from BIM models to energy analysis software.
Definition & Context
gbXML (Green Building XML) is an open schema for passing building geometry, zoning, and HVAC/energy attributes from BIM/CAD tools to building-performance and energy-analysis software (EnergyPlus-based engines, IES VE, Autodesk Insight/Green Building Studio, OpenStudio). It is the de-facto interchange for early-stage energy modeling.
A gbXML file describes spaces, bounding surfaces (walls, roofs, floors, openings), their adjacencies and constructions, and thermal zones — not detailed solid geometry. Authoring tools such as Revit and ARCHICAD export gbXML from a simplified energy/analytical model derived from the design model.
Why It Matters
gbXML lets architects run energy and daylighting analysis without re-modeling the building in the analysis tool, so sustainability feedback happens during design rather than after. Its accuracy depends entirely on a clean analytical model — correctly bounded rooms/spaces and valid surface adjacencies.
Because it is a neutral interchange, one export can feed multiple analysis engines, which is why it underpins comparative early-stage studies and green-building documentation.
Best Practices
- Build and validate the analytical/energy model (spaces that fully enclose each zone) before exporting
- Verify surface adjacencies and that every space is closed; gaps create unbounded zones and bad results
- Set realistic space types and constructions so exported loads are meaningful
- Validate the exported file in a gbXML viewer before handing it to the analysis team
Common Pitfalls
- Exporting from an unresolved model — missing or overlapping spaces give meaningless energy results
- Assuming detailed geometry transfers; gbXML is a simplified zone/surface model, not the full BIM
- Forgetting units, location, and weather data that the analysis engine needs alongside the geometry
Standard Engineering Workflow for gbXML (Green Building XML)
2. Geometric Alignment & Profile Design
Lay out horizontal tangents and spiral transitions following AASHTO / Eurocode minimum curve radii, coupled with vertical slope crest/sag parabolic curves.
Common Failure Scenarios & Troubleshooting
| Failure / Geometric Issue | Root Cause & Mitigation Strategy |
|---|---|
| Surface triangulation bridges across steep ravines incorrectly | Add linear Breaklines along tops/toes of slopes or specify 'Maximum Triangle Length' under Surface Build Properties. |
| Horizontal curve radius triggers AASHTO violation flags | Adjust minimum transition spiral length or increase curve radius to meet minimum design speed superelevation criteria. |
| Coordinates offset by several meters after CAD/GIS import | Verify projection datum and false easting/northing parameters in MAPCSASSIGN before importing geospatial shapefiles. |
Industry Standards & Compliance Codes
- Eurocode 7 (Geotechnical Design - EN 1997)
- ISO 19650 (BIM for Civil Infrastructure)
References & Further Reading
Related Concepts
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