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Saturday, 30 August 2014

Top Rails in Revit Railings


Revit 2013 introduced a whole new way of building stairs.  At the same time some subtle changes were made to railings in Revit - in particular the new concept of a "Top Rail" as a separate sub-component of the railing definition.  This can cause confusion as the old rail structure still remains in Revit, and the two methods can sometimes perform the same function - but with different behaviour. . . . . .

The railings type properties dialog boxes have always been complex (particularly balusters, but that is another matter).
  • Old style horizontal rails in a railing family:

  • Horizontal Rail Structure in old style railings:
  • From Revit 2013 new properties were added:  "Top Rail", "Handrail 1" and "Handrail 2".  For the moment we are only interested in the Top Rail, which can do the same job as the highest rail (old style), including controlling baluster heights.  Even if you upgrade an old project (or template) you may not see the new properties on old railings - you have to swap them over for new railing types that are supplied in the new project templates (and then match all the other settings you want).

  • Top Rail properties in a Railing only have two settings - a height and a Type.  By default the type is set to "None", which means you won't get anything.

  • You have to select from a drop down menu to get a predefined top rail type.  You cannot change the properties of the top rail here.
  • It is the same old three-step trick in Revit:  close the dialog box, go to the Project Browser, find the new "Top Rail Type" system family (subset of Railings category) - modify, duplicate, rename etc.  It will have some interesting new properties - the most important being "Profile" where you can select a 2d profile family (another 3 steps to change that if you need to!);  other interesting properties include Extensions and Terminations, but that is for another time.
  • One other important property is "Transitions", which controls how the top rail behaves at changes of angle in the rail.  What this does will be demonstrated in the next blog post.

The new Top Rail and old Rail structure can coexist, or you can have one or the other;  you cannot have neither though, as the railing must have at least one horizontal component.  Depending on which combination you have, Revit will give quite different results, and can display some weird behaviour - to be described in following blog posts: