Built-In Parameters

These are hard-baked into the Revit software - we can't define or delete them

Introduction

Built-in parameters (written BuiltInParameter) are a special kind of parameter and the only kind of Revit parameter which cannot be modified in any way (even by us programmers).

These are used to refer to many hard-coded parts of the application that we can't change. For instance, family instances will have a few parameters we can't remove, no matter how we try. This could be a 'Mark' or an 'Offset from Level' value.

The BuiltInParameter Enumeration

Since the list of BuiltInParameters is hard-coded, it makes sense to store these in an enumeration. The names of each parameter may differ slightly from how they appear in the user-interface, so each BuiltInParameter is stated alongside its UI-name. Each parameter has an underscore-separated name written in all-capitals.

For instance, say we wanted to read the sill height from a window we've placed (as in this example from the excellent spiderinnet blog), we could use:

#Boilerplate Code
my_window = UnwrapElement(IN[0])
sill_height = my_window.get_Parameter(BuiltInParameter.INSTANCE_SILL_HEIGHT_PARAM).AsDouble()
OUT = sill_height

While there is no foolproof, easy way to identify the BuiltInParameter you're looking for, the following steps may help:

• Find the name the parameter is referred to in the UI and use a CTRL+F search in the BuiltInParameter Enumeration page of APIDocs.co.

• Run a quick Google search to see if others have already asked the same question.

• Use the excellent RevitLookup add-in for Revit. Harry Mattison of BoostYourBIM has created installers for each version, making installation quick and easy.