Parameters in Revit, Part 2: Parameter Types
Parameters are a deep topic in Revit and understanding them is foundational to using the software effectively. While this is a longer blog post, it is still only a shallow dive into the subject matter.
For a basic refresher on what a parameter is, please refer to part 1 of this series.
In today’s blog post I will be discussing the different types of parameters in Revit: System, Family, Project, Shared and Global Parameters.
To understand these parameter types, it’s helpful to think about why we assign parameters to elements in our models.
Parameters can drive the characteristics of modeled geometry – size, shape, material, etc.
Parameters allow us to sort, quantify and itemize element data in the model through schedules.
Parameters allow us to visually identify elements or features of elements through annotative tags in our model.
Due to these common uses of parameters, the ability to schedule or tag a parameter is an important factor in why we choose one parameter type over another.
To understand which parameters can be scheduled or tagged, it’s important to know:
Where the parameter is defined
Which file or files are aware of and can utilize the parameter data
The following is a summary of each parameter type in Revit:
System Parameters
The system parameter is often overlooked when discussing parameters and it is not covered in the Autodesk Revit help documentation. The only resource I found when I was initially learning parameters was a blog post from Paul Aubin. I encourage everyone to read that post.
System parameters are built into Revit project and family files. The parameters themselves cannot be modified, renamed, or deleted - only the value of the parameter can be set.
When you choose a specific family category template to start a family in Revit, the system parameters are predefined.
System parameters can be scheduled and tagged.
An example of a system parameter is the “Thermal Resistance (R)” parameter in the door family category. If you start a new door family from the door template, that parameter is already predefined, and you can’t delete it or change it.
If you create a new door tag family, you can automatically use the Thermal Resistance (R) parameter in a label for tagging.
Similarly, you can add the Thermal Resistance (R) parameter to a schedule in a project file.
Revit is universally aware of system parameters throughout the project and family environment.
Family Parameters
Family parameters are created within the family editing environment and are used to drive a characteristic of the family.
Family parameters can’t be tagged or scheduled within the project environment. The Revit project is not aware of these parameters.
Because of this limitation, family parameters are best suited to defining aspects of the family that are only important to the internal functioning of the family.
For example, if you are building a base cabinet family, you might use a family parameter to define the width of the stile and rail of the cabinet door. This dimension might not be appropriate in a schedule, but you would want the geometry to be accurate in your model views.
Project Parameters
Project parameters are defined within the project environment and can be associated with one or more categories of families (including views and sheets).
When you associate a project parameter with a family category and select an example of that family, you will see the parameter in the properties palette for instance parameters or in the family types dialog for type parameters.
Project parameters can be scheduled. The Revit project is aware of these parameters because they are defined in the project. When you create your schedule, you can add the parameter as one of the fields.
Project parameters can’t be tagged because they do not exist in the family or the annotation tag for the family.
A common use of project parameters is in door schedules. While each office will have different standards, there is a common practice of listing typical detail references for the door head, jamb and sill.
The door family and door tag don’t need to know about the detail references to function. The only place that the information is important is in the schedule. So, project parameters can be created for the detail references and added to the door category in the project file.
Shared Parameters
Shared parameters can cause confusion and consternation for newer Revit users. This is because it can be unclear when to use them and because the management of shared parameters often falls to the office BIM Manager*.
*Always check with your office BIM Manager (or whoever manages them) when you encounter a potential shared parameter situation.
A shared parameter can be defined either from the family editor or from a project file. The shared parameter definition itself is saved to an external text file – the shared parameter file*.
*Autodesk introduced a new service where shared parameters can be stored in the cloud, but for the purposes of this post we will focus on the locally stored text file.
The shared parameter file is a simple .txt text file and you can open it to look at what information is stored in it however, please note that you should never edit the contents of the shared parameter file in the text editor.
When you define a shared parameter, it can be added as a shared family parameter and a shared project parameter. By adding the shared parameter to your family, family tag and project, you can tag and schedule the parameter in your project.
When you create a shared parameter, it must be assigned to a group in the shared parameter file, so be aware that you must first create a new group or select an existing group.
There are different conventions about shared parameter group organization. One convention is that you name shared parameter groups according to the associated family category like Rooms, Windows, Doors, etc…
Here are a few items to note about shared parameters:
The best practice is to have one shared parameter file per office (not per project).
Revit remembers and will load the last shared parameter file you opened - the path to a specific shared parameter file is not saved in the project file.
Shared parameter names must be unique, even if they are in different groups, so it’s a good idea to add enough descriptive words or characters to differentiate the parameter (don’t use “Finish”, use “Room Floor Finish” or “RoomFloorFinish” etc.)
Not everything needs to be a shared parameter. Typically, only items that need to be tagged or show up in a label between multiple files require a shared parameter.
In my experience, the biggest source of confusion in parameters is between system parameters and shared parameters. System parameters can be tagged and scheduled by default, but users will not find the system parameter definitions in the shared parameter file. Because system parameters behave like shared parameters and are not really explained anywhere in the Autodesk documentation, it muddies the waters of when you need a shared parameter.
Global Parameters
Global parameters are defined within the project environment and can be used to drive the value of one or more elements in Revit.
Global parameters are not assigned to specific family categories like project parameters.
Global parameters can be associated with instance or type parameters of certain family parameters. If you see a button next to the far right of a parameter, you can click the button and link it to a Global parameter.
Global parameters with a dimensional datatype can be used in dimension labels to drive a specific value for the dimension.
Global parameters are helpful because when they are used strategically on multiple elements, they can update all of the elements quickly.
In future posts, we will look at each parameter type in more detail.
That’s all for now.