Revit API: How to change associated Level in Walls?

Check out this snippet with explanation to change top and base constraints of a Wall.

Get Parameters

First of all we need to have an element that we are going to modify. I am going to get a wall with an ElementId
Then we need to look inside and find parameters that we want to modify. You can do it easily with RevitLookup plugin that let's us Snoop Current Selection

Then if you click on Definition you can see BuiltInName of this Parameter. Which is - WALL_BASE_CONSTRAINT

Then do the same to find names of Top Constraint parameter and Unconnected Height

Revit Lookup - Wall Base Parameter - BuiltInParmater.png

Since these are BuiltInParamteres we can get them with .get_Parameter() method

# Get Wall
wall = doc.GetElement(ElementId(346574))

# Get Wall Parameters
wall_base   = wall.get_Parameter(BuiltInParameter.WALL_BASE_CONSTRAINT)
wall_top    = wall.get_Parameter(BuiltInParameter.WALL_HEIGHT_TYPE)
wall_height = wall.get_Parameter(BuiltInParameter.WALL_USER_HEIGHT_PARAM)

Set New Levels

To set new levels we just going to take parameter variables we have written already and use .Set() method and provide ElementId of new levels.

# Choose New Levels
    new_base_level = lvls[2] # I am taking random level
    new_top_level  = lvls[3] # I am taking random level

    # Set New Associated Levels
    wall_base.Set(new_base_level.Id) # Set Base
    wall_top.Set(new_top_level.Id)   # Set Top

Set Wall Top Constraint to None

If you want to change Top Constraint to None we need to provide ElementId(-1) instead of Level.Id This is equivalent to None in Revit API.

# SET TOP: Unconnected Height
wall_top.Set(ElementId(-1))      # Set Top: None
wall_height.Set(20)              # Set Unconnected Height (20 feet)

Final Code:

# -*- coding: utf-8 -*-
# Author: Erik Frits

from Autodesk.Revit.DB import *

# ╦  ╦╔═╗╦═╗╦╔═╗╔╗ ╦  ╔═╗╔═╗
# ╚╗╔╝╠═╣╠╦╝║╠═╣╠╩╗║  ║╣ ╚═╗
#  ╚╝ ╩ ╩╩╚═╩╩ ╩╚═╝╩═╝╚═╝╚═╝
#====================================================================================================
doc   = __revit__.ActiveUIDocument.Document
uidoc = __revit__.ActiveUIDocument
app   = __revit__.Application

# ╔╦╗╔═╗╦╔╗╔
# ║║║╠═╣║║║║
# ╩ ╩╩ ╩╩╝╚╝ MAIN
#====================================================================================================
# Get Levels
lvls = FilteredElementCollector(doc).OfCategory(BuiltInCategory.OST_Levels)\
                                       .WhereElementIsNotElementType().ToElements()

# Create Transaction to make changes in the project.
with Transaction(doc,__title__) as t:
    t.Start()

    # Get Wall
    wall = doc.GetElement(ElementId(346574))

    # Get Wall Parameters
    wall_base   = wall.get_Parameter(BuiltInParameter.WALL_BASE_CONSTRAINT)
    wall_top    = wall.get_Parameter(BuiltInParameter.WALL_HEIGHT_TYPE)
    wall_height = wall.get_Parameter(BuiltInParameter.WALL_USER_HEIGHT_PARAM)

    # Choose New Levels
    new_base_level = lvls[2] # I am taking random level
    new_top_level  = lvls[3] # I am taking random level

    # Set New Associated Levels
    wall_base.Set(new_base_level.Id) # Set Base
    wall_top.Set(new_top_level.Id)   # Set Top

    # SET TOP: Unconnected Height
    wall_top.Set(ElementId(-1))      # Set Top: None
    wall_height.Set(20)              # Set Unconnected Height (20 feet)

    t.Commit()


# Author: Erik Frits

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