Parameters in Revit, Part 1

Parameters in Revit can be confusing for new users. Even users with a lot of experience can find it confusing.

I’ve used Revit for over 8 years and here’s my explanation of what parameters are and how they work.

What is a Parameter?

A parameter is a named container for a piece of information (or “data”). You first assign a name to the container and then you store a value in the container.

In computer science, it’s known as a variable.

For example, you are working on project with a door that has a 36” wide door panel. You also have another door that has a 30” wide door panel.

Hypothetically, you could create two different door families with two different door panel widths (but please don’t because it’s bad practice).

Or

You can create a parameter called “Width” and assign it to the dimensional width of the door panel geometry.

Now you can create different types of doors from the same door family that have different width door panels.

This is what’s meant when we say a family is “parametric”: it has parameters assigned to certain geometric and informational characteristics that can be used to create a range of objects with varying values.

Data Type

A parameter is configured to hold a specific type of information. The type of information that’s stored is called the Data Type.

In the door panel example above, the width parameter has a data type of “Length” because we need to store a dimensional length for the door panels: 3’-0” or 2’-6”.

If you entered a value that was not a length, it wouldn’t make sense to Revit and you would get an error.

              You can’t enter “sorta big”, 100 s.f. or 15 degrees.

Revit has a number of data types, so think about the type of information you need to store when creating a parameter: text, length, angle, area, number, integer, yes/no…

Type vs Instance

As we go down the parameter rabbit hole, the next potentially confusing choice you need to make is: should it be a type parameter or an instance parameter?

Every element in a Revit model has type parameters and instance parameters.

Type Parameters

If you need to create multiple copies of something that all have the same characteristics, you will choose type parameters to control these characteristics.

For example, if you need to create multiple 16” x 24” concrete columns in a garage, the length, width and material of the column will be Type parameters.

Instance Parameters

If you need each individual copy (or instance) of an element to have a unique characteristic or value, you should create an instance parameter for this value.

For example, if you need to number each column sequentially, the column number should be an Instance parameter.

There are gray areas and additional complexity about how and when to use type vs instance parameters, but we will cover it in another post.

In Part 2, we will go deeper into parameter types like System, Project, Shared and Family so stay tuned.