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Molding

Getting started

Open the app. The workspace has three columns:

  • Left — the family catalog (click one to open it) and a New button (creates a blank family instantly with the Metric Generic Model template).
  • Middle — the 3D viewport, showing your family live.
  • Right — the editor panel: a toolbar plus four tabs, Parameters, Types, Materials (the family's materials and subcategories), and Generators (where the geometry lives — its list is headed Elements).

Build a door panel, step by step

This walks the whole loop once. Every control named below is a real button in the panel.

  1. Start a new family. Click the file icon in the toolbar (tooltip New graph). In the New Graph dialog type a Name, pick a Template (Metric Generic Model is fine), then Create. Parameters and Generators start empty.
  2. Add the driving parameters. On the Parameters tab click + and choose Length. A row appears — click its key and rename it Width, then type 900 in the value cell next to it. That value belongs to the family type named in the dropdown at the top of the tab (a new family starts with one called Default) — in Revit a value always lives on a type, never on the parameter. Repeat for Height (2100) and Thickness (45). Leave the row's ⚙ → Instance box clear: these are type parameters, which is what lets the derived parameter in the next step read them (see Parameters & coordinates).
  3. Add a derived parameter. The panel sits centred, so we need half its height. Add another Length, rename it HalfHeight, and in its ⚙ popover type Height / 2 into Formula. Its value cell now shows the formula, greyed out — Revit computes it, so no type stores a value for it. (Math lives in formulas, not in geometry fields — and a formula is written in Revit's formula language, not JavaScript. See Parameters & coordinates.)
  4. Draw the profile. Switch to the Generators tab. Click +, and under SHAPE pick Rectangle. A rectangle element is added.
  5. Make it follow the parameters. Click the rectangle row to select it — its fields expand. Each coordinate field has two buttons, V (a fixed value) and P (follow a parameter). For width click P and choose Width; for height choose Height; for the center's Y choose HalfHeight. Leave center X on V = 0.
  6. Give it depth. Click + again and under FORM pick Extrusion. Select it; in the profile checkbox list tick your rectangle, and set depth to P → Thickness. You now have a 3D door panel.
  7. Tune it live. Back on Parameters, change Width to 1000 — the panel widens in the viewport instantly. That is the whole parametric loop, before Revit.
  8. Add size variants. On the Types tab add more named types like 900 × 2100, each with its own set of values — the user picks one when placing the family. Each card's radio button makes that type the one the editor (and the viewport) shows.
  9. Save / export. The disk icon (tooltip Save JSON) downloads the family as a .json file. To produce the real .rfa, open the family in the Molding Revit plugin and press the ▶ button (tooltip Generate .rfa (requires Revit)).

In the browser you design and preview. The actual .rfa is produced by the Molding Revit add-in — this same editor inside a Revit panel, where the Generate button is enabled.

Grab it from the Revit Plugin page. New to the V / P toggle? It is the core idea — read Parameters & coordinates next.

📖 3 min read