TL;DR
A Yes/No parameter is a boolean switch, and any comparison is already a Yes/No formula: Show_Rail = Height > 2100mm needs no IF around it. Assign Yes/No parameters to geometry's Visible property to make parts appear and disappear automatically, chain them with AND/OR/NOT for compound rules, and use paired opposite toggles to switch between alternative geometry sets — the pattern behind every configurable family.
Key Takeaways
- ✓A comparison is already a Yes/No value — Show_X = Width > 900mm needs no IF wrapper.
- ✓Assign a Yes/No parameter to the Visible property and geometry manages its own appearance.
- ✓Visibility formulas hide geometry but Revit still calculates it — flexing stays safe.
- ✓Paired opposite toggles (Show_A / Show_B = NOT(Show_A)) switch between alternative geometry cleanly.
- ✓Yes/No formulas toggle nested family instances on and off for configurable components.
- ✓Grey out user toggles by giving them formulas — a formula-driven parameter becomes read-only.
Yes/No parameters look like the humblest data type in Revit — a checkbox. But wire formulas into them and they become the family's nervous system: parts that know when to appear, options that exclude each other correctly, and nested components that switch themselves on exactly when conditions demand.
The Key Insight: Comparisons Are Already Yes/No
The most common beginner formula wraps a comparison in a redundant IF:
Height > 2100mm evaluates to yes or no directly. Every comparison operator works: >, <, =, >=, <= — on lengths, numbers, integers, and even text.
Automating Visibility
In the Family Editor, select geometry and find the Visible property. Click the small associate button and link it to a Yes/No parameter. Now the parameter's formula decides whether that geometry appears in the project:
Good to know: hidden geometry is still computed by Revit — its dimensions must remain valid even while invisible. A hidden part with a broken constraint still breaks the family.
Switching Between Alternatives
Configurable families often need either A or B, never both — a flat top or a sloped top, a painted or a raw finish. The clean pattern is one driving toggle and one derived opposite:
Because Show_Flat_Top is formula-driven, users can't accidentally check both boxes — Revit greys out any parameter that has a formula. That greying-out is a feature: giving a parameter a formula is how you take it away from the user.
Compound Rules With AND, OR, NOT
These are the same logical operators from the IF statements chapter — but without the IF, because the yes/no result is the goal itself.
Toggling Nested Families
The real configurator pattern: load alternative components as nested families, place them in the same location, and drive each instance's Visible property with a Yes/No formula. One integer or length parameter then switches the whole assembly:
The user sets Handle_Code once; exactly one nested handle family appears. When the option list grows beyond a handful, the codes and their associated dimensions usually migrate into a CSV lookup table — Chapter 9's territory.
Reporting the State in Words
A Yes/No state often needs to appear in schedules as language, not a checkbox. Pipe the toggle through a text formula — IF(Is_Fire_Rated, "FD30", "STANDARD") — as covered in the text parameters chapter.
Chapter 7 of 10
Families that configure themselves
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