Weird Stuff with Revit Shared Parameters

When you create a suite of similar parametric families (say windows), you will define a series of parameters that control the families in the project - it may be dimensions, visibility switches etc.  If those are instance parameter, there is a really important choice you have to make:

• Should they be "Shared Parameters" or just regular "Family Parameters"?

Conventional wisdom says that you only need to make them shared if you want to tag or schedule them in the project.  However, there are some other critical differences in behaviour that may affect your decision:

Did you know that when you make them 'Family Parameters', then start using the families in the project and swap them over for similar families with identical parameters - Revit loses the  data held in the instance parameters - even if the instance parameters are identically named in the families?  Aargh!!  That is not good news.  This even happens if the families were cloned from one source that already had the parameters set up.

However, if you used 'Shared Parameters' that instance property data is maintained when you swap family/types (provided that the same shared parameters are defined in each of the families).

Here is another reason for using shared parameters even when you don't need to tag or schedule them.