When modelling Cable Ladder in Revit, the Width parameter refers to the external width of the ladder. Unlike pipework, there is no Internal Width parameter available.
However, in industry standards for cable containment systems—including ladder, tray, and basket—the internal width is the critical dimension, as it defines the cable carrying capacity. The external width is largely irrelevant for engineering and construction purposes.
This limitation in Revit causes significant issues in design, coordination, and construction workflows. Since the Width parameter is the only one available for tagging, scheduling, take offs etc, models built using out-of-the-box families often contain a consistent 50mm error (25mm per ladder wall). As a result, LOD 300 design models frequently require substantial rework and re-coordination at the construction stage to avoid clashes, leading to unnecessary effort and cost.
This is core functionality that already exists for ductwork and pipework, so there’s no technical reason it shouldn’t be extended to cable containment. The default Width parameter should represent internal width, or at minimum, Revit should expose both internal and external width parameters.
Note: I'm aware of the existing workarounds, plugins, and alternative approaches, but all introduce time costs and additional risk. Examples include:
- Creating a shared parameter for internal width - Only project based, cannot be family based, which must be manually or Dynamo-updated (risk of human error or outdated data)
- Using manual text parameters (high risk and not recommended).
- Relying solely on cable tray fittings (not feasible when receiving models from external design teams using default Revit families).
- Switching to Fabrication MEP containment (our current approach), which requires deleting and remodelling ladders, as Revit does not support conversion from standard to fabrication containment. If you're a design firm then all design teams use the same Fabrication MEP catalog, which is unrealistic.
This is a fundamental issue that affects many users and projects. A native solution within Revit would significantly improve accuracy, reduce risk, and streamline workflows across the industry.
