My experience has been that it is often easier to place an item close to where I want it, and then adjust its position afterwards, to get it exactly where I want it, than it is to try to place the object precisely initially. The temporary dimensions that Revit displays when selecting an object are very useful in making that final adjustment efficiently.
Those temporary dimensions will measure to a Wall's centerline, regardless of the justification used to place the Wall. But you can use the round blue grips that appear on the witness lines of the temporary dimension to reposition the witness line(s), if desired. The witness line that is on the selected object can only be moved to other positions (if any) on the selected object. The other witness line can be moved to have the dimension measure to a different object that the initial one Revit chooses. When moving a witness line with the grip, if the target object is a Wall, Revit will again favor the centerline. To select another position on the Wall, such as the face of the Wall, hover the cursor near the desired face and then tap the TAB key. The highlight will shift from the Wall centerline to the Wall face, and if you then release the left mouse button, the witness line will reference that face.
NOTE: If you have multi-component Walls, and the View displays the common edges between components, you can also tab to those edges. You may want to activate Thin Lines and be zoomed in when doing the tabbing so that you are certain you are getting the desired location for the witness line.
This brief Screencast shows how a Wall can be placed at a desired clear face-to-face distance from another Wall using the techniques noted above. If the image is too small to see when viewing it embedded in this post, you can expand it to full screen by selecting the double diagonal arrow icon at the right side of the black bar below the Revit window in the Screencast.
David Koch
AutoCAD Architecture and Revit User
Blog | LinkedIn
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