Revit plugin
Molding uses a two-step flow: you design the family in the browser editor, then a Revit add-in reads the design and generates the .rfa.
Install
- Close Revit.
- Download Molding for Revit (Windows installer,
.msi) and run it. It installs for your Windows user only — no administrator rights needed. - Start Revit. The first time, Revit asks whether to load the add-in (the installer is not code-signed yet): choose Always Load.
- A Molding tab appears on the ribbon. Pressing F1 on its button opens this page.
Supported versions: Revit 2022 – 2027. Revit LT cannot run add-ins; families you download from the library still open in it.
Uninstall: Windows Settings → Apps → Installed apps → Molding for Revit → Uninstall.
From source (developers): .\revit\install.ps1 <RevitVersion> registers a local build; .\revit\install.ps1 -Uninstall removes it.
Opening the editor inside Revit
Click Molding on the ribbon. The same editor you use in the browser opens as a panel inside Revit — same interface, same files, same JSON. You can load any family you designed online by copying its JSON file into the panel.
In panel mode the interface switches to a tabbed layout:
| Tab | Contents |
|---|---|
| Design | The 3D viewport + the Parameters / Types / Generators editor panel |
| Catalog | Browse and place pre-built shared families. Export All… batch-generates every catalog family as .rfa files to a local folder. |
Toolbar buttons
The toolbar buttons are icon-only; the names below are their tooltips.
| Button | Tooltip | When it is enabled | What it does |
|---|---|---|---|
| ▶ | Generate .rfa (requires Revit) | Running inside Revit and a family is open | Creates or re-creates the .rfa via the Revit Family API |
| ↻ | Update .rfa (dirty changes) | Inside Revit and the design has changed since the last Generate | Re-runs the same generation; a run with nothing dirty returns immediately without touching the file |
| 📄 | New graph | Always | Opens the New Graph dialog (Name, Template, Create) |
| 💾 | Save JSON | Always | Downloads the family design as a .json file |
End-to-end workflow
- Design — open or build a family in the browser or in the Revit panel.
- Generate — click ▶. Molding opens the
.rfttemplate, builds the graph, saves the.rfato the output path and closes the document again. Nothing is left open in the Family Editor. The family is saved only when every part of the graph made it into Revit as declared: if a node, a constraint, a formula or a property could not be built, generation stops with an error naming it and no.rfais written — you never get a family that silently differs from the design. - Load into a project — in Revit, open the generated
.rfaand use Load into Project. Place it like any Revit family. - Edit — change parameters or geometry in Molding, then click ↻. The
.rfais regenerated from scratch and overwrites the previous file at the same path.
The generated family is fully parametric: Revit's own solver handles recomputation when parameters change. No Molding plugin is needed at runtime — only at generation time.
The generated .rfa
Molding generates the full constraint apparatus for you:
- Reference planes — one per unique parametric coordinate axis. These construction planes are set to Not a Reference, so they never show up when you dimension or align to the family in a project. The reference planes you add yourself (Reference Plane node) keep the name and Is Reference strength you give them, and follow their offset parameter.
- Dimensions — labelled and associated to their parameters.
- Family parameters — fully wired so Revit's solver flexes the geometry.
- Voids — a form with Solid switched off cuts every solid form it overlaps, exactly as in the preview.
- Thumbnail — the family's preview image (Load Family dialog, Windows Explorer) is rendered from its 3D view, shaded with edges.
Family Category and Parameters
The Types tab's FAMILY section holds Revit's own family switches — Work Plane-Based, Always Vertical, Cut with Voids When Loaded, Shared and Room Calculation Point. Each is a three-way dropdown:
- Template — leave the
.rft's own setting alone. This is the default. - Yes / No — set the switch explicitly on the generated family.
These are plain on/off switches on the family, not parameters: Revit offers no way to associate one to a family parameter, so they cannot flex per type or per instance. If the template's category does not offer a switch you set, generation stops with an error naming it rather than ignoring you.
The Family Editor file will be dense (many planes and dimensions), but nobody reads it. The Molding node graph is the design surface; the .rfa is a generated artifact.
Saving and loading JSON
Save JSON(💾) exports the family as a.jsonfile you can share or check into version control.- To reload: open the family from the Catalog (or My models in the browser).
- Families in the browser catalog can be forked (click the fork icon on a catalog card in the left sidebar) and customised as your own. The Revit-side Catalog panel has no fork button — its cards only offer Place.
Troubleshooting
Generate button is greyed out — the panel is open in the browser, not inside Revit. The Generate button is only active when Molding is running as a Revit panel.
"Cannot generate: … references unknown parameter …" — a node field references a parameter key that does not exist. The graph is validated before anything is sent to Revit, and the failure appears as a notification naming the offending node, field and key. Check the Parameters tab for typos.
Geometry looks wrong in the preview but correct in the .rfa (or vice versa) — the web preview and Revit each evaluate the same JSON, but the preview is approximate for some forms (revolution, sweep). The .rfa is authoritative.
Flexing fails after load — check that the family parameters in Revit's Manage → Family Types panel match the parameter keys in Molding. If you renamed a parameter, re-generate rather than update.