Families, Parameters, and Content Creation

What Is a Revit Family?

In Autodesk Revit, almost every object you place in a model—a pump, a machinery base, a structural pad—comes from a family. A family is a reusable parametric definition that stores geometry and the rules that control it. When you change a parameter value, the geometry updates automatically. This is the core idea behind Building Information Modeling (BIM): intelligence lives inside the object, not just its shape.

Revit ships with thousands of pre-built families, but manufacturing and marine projects frequently require custom content. A machinery base on a vessel deck, an equipment isolation pad in a fabrication plant, or a custom pipe support may not exist in any library. Learning to build your own families is therefore an essential skill in this trade.

The Family Editor

The Family Editor is a separate Revit environment you enter whenever you open or create a family file (.rfa extension). It has its own ribbon, its own Project Browser (showing views like Front, Right, and Ref. Level), and its own rules.

You always start from a family template (.rft file). The template you choose sets the category—Generic Model, Mechanical Equipment, Structural Foundation, and so on—and provides the reference planes and default views you need. For a generic machinery base or marine equipment pad, the Generic Model Metric template is a practical starting point because it imposes no category-specific hosting rules.

Reference Planes and Sketching the Extrusion

Before drawing geometry, experienced drafters place reference planes to act as construction lines. In the Family Editor, reference planes are the anchors to which you lock dimensions and parameters. A well-built family has its geometry constrained to reference planes, not to other geometry—this prevents failures when values change dramatically.

To create a rectangular pad:

1. In the Family Editor, go to the Ref. Level floor plan view.

2. Draw four reference planes to define the four edges of the pad—two for length (left and right), two for width (front and back).

3. Use Create → Extrusion to sketch a rectangle snapped to those reference planes.

4. Set the extrusion height numerically for now; you will replace that with a parameter next.

Lock each sketch line to its reference plane using the small padlock icon that appears after you align and select the line. If lines are not locked, the family will flex incorrectly or produce constraint errors.

Parameters: Types vs. Instances

A parameter stores a value that drives geometry or data. Revit families support two scopes:

• Type parameters are shared by every family instance of the same type. Changing a type parameter changes all matching instances at once.
• Instance parameters are unique to each placed instance. You can give one pump pad a length of 1200 mm and a neighboring pad a length of 900 mm without creating separate family types.

For this exercise you will use instance parameters named `Pad_Length`, `Pad_Width`, and `Pad_Height`. Instance parameters appear in the Properties palette when you select a placed instance in a project, making them fast and intuitive to edit on the drawing sheet.

Creating and Assigning Parameters

To add a labeled dimension and link it to a parameter:

1. In the Family Editor, apply an Aligned Dimension between two reference planes (for example, the left and right planes for length).

2. Click the dimension label (the small gray tag that says "EQ" or shows a number).

3. In the dialog that appears, choose Add parameter, name it `Pad_Length`, set the discipline to Common, type to Length, and select Instance.

4. Click OK. The dimension label now shows `Pad_Length`.

5. Repeat for width (`Pad_Width`) between the front and back planes.

6. For height, go to an elevation view, dimension the extrusion top to the Ref. Level, and assign `Pad_Height` the same way.

After assigning all three parameters, use Family Types (on the Properties panel) to test: enter values for `Pad_Length`, `Pad_Width`, and `Pad_Height` and click Apply. The geometry should flex without error messages. If Revit shows a constraint error, check that all sketch lines are locked to their reference planes.

Loading Into the Project and Placing Instances

Once the family passes testing in the Family Editor, click Load into Project on the ribbon. Revit returns you to the open project and prompts you to place the family. Place two instances in the manufacturing building floor plan. Select each instance separately and change its parameter values in the Properties palette. Verify visually that the geometry on screen reflects the values you entered—different lengths, widths, or heights should be clearly visible.

Save both the family file (.rfa) and the project file (.rvt) before the instructor check.

Naming Conventions and File Hygiene

Use clear, consistent parameter names. Underscores instead of spaces (`Pad_Length` not `Pad Length`) prevent scripting errors if the family is later used with Dynamo or other automation tools. Save your family to the class shared folder with your initials and today's date in the filename—for example, `MachineryPad_JT_2025.rfa`.

Workstation Safety

CAD and BIM work involves extended time at a computer workstation. Follow ergonomic best practices: adjust chair height so your feet rest flat on the floor, position the monitor at or just below eye level, and take a short break every hour to prevent repetitive strain. Report any electrical concerns—frayed cables, sparking outlets—to the instructor immediately; do not attempt repairs yourself. Lockout/tagout procedures govern the live equipment you will eventually draft; always read the relevant safety data before visiting any shop floor to gather field measurements.