Tuesday, February 19, 2013

Mullion Halves

In the prior post, Wall Joins, John enquired about my work procedures and using "half the mullion" on adjacent walls. Here's his actual question:

How does half a mullion work? I assume you would still have to dis-join the walls still. Plus half a mullion on each wall creates (in my mind) an "L" shaped mullion and not a square shaped mullion. Personally I use one curtain wall without a mullion and the other with the "square" end mullion. Then I just align the curtain wall mullions together (outside faces). Everything from that point on looks perfect in 2D views... and even in 3D.  John"

 We accomplish this by creating the profile for the male mullion half and assigning it to one wall and assign the female half to the adjacent wall.  The end points of the walls need to be separated when the mullions are assigned but are moved together after.  The figure below shows half of one mullion at an outside corner.

The figure below shows the adjacent curtain wall with the other mullion half assigned as the mullion profile.  Remember, the endpoints should no be co-located  when assigning the millions.

When finished, and the endpoints share a common location, the corner looks like the figure below.

Why is this preferable to assigning a single mullion to one curtain wall and leaving the adjacent curtain wall without a mullion?  That would require that the edge handle of the CW without the mullion to be manually aligned to the edge of the mullion where it crosses the panel's path; a feature that should be automatic in Revit.  Changes to the mullion profile won't necessarily be reflected in the open-ended CW and is an opening for errors.  The figure below shows a similar scene with a single, full mullion at the edge of one of the curtain walls.


  1. John, Your blog is surely very good, but the title is seriously misleading. It should be clearly stated taht you are talking about Revit issues, not BIM.

    1. Anonymous,
      Revit is what we do best, but we'll cover more than just Revit in our blog. If there is something you would like covered, or would like to contribute, please let us know.

  2. John,

    It is great to see a Revit Blog directly addressing Curtain Wall in Revit. I look forward to reading and sharing experience on this matter as the blog continues.


    Gregg Haeberle
    VD&C Manager
    Juba Aluminum Products

    1. Thanks Gregg,
      If you have an issue or solution that you would like to share, please feel free to send it to me. We'll try to make this community as strong as possible.
      Thanks again,

  3. Jon
    2 Things I found "not great":
    1. Are the fact that there is an overlap of "frame detail". I've found over the years that if there's an opportunity to screw up something like "overlapping" details (or that it isn't simple) the less experienced draftsperson will not pay the attention that is due to this kind of solution.
    2. You've shown a 45 degree corner mullion, that's not always the case, most times I've used corner mullions that had a rectangular "box frame", and sometimes they are not evenly (glass) set back. This was the situation I was interested in how you solve as half mullions.


  4. Hi John,
    Thanks for the comments.
    1. We try to represent the mullions as accurately as possible while balancing the modeling restrictions of Revit and the file size/system resource requirements of a highly detailed model. The portion that overlaps is one element of the male vertical that is clipped to the female vertical. The portion that overlaps is a detail line and not part of the mullion profile. No parts of the adjacent profiles actually cross each other.
    2. Send a file of the situation (preferably Revit or AutoCAD) and I'll take a look at it. The email link is near the bottom right corner of the header graphic above.

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  6. Hi Jon,

    I am very pleased to see a blog dedicated to curtain walls in Revit, an often overlooked but tricky aspect of the software. I will be adding you to my reading list and look forward to future posts.

    Thanks for the comment on my blog and also taking time to share your knowledge.

    Ben - BIMopedia.com

    1. Ben,

      We're trying to fill a need out there for Revit CW information and techniques. If there is a topic that you would like covered on the blog, please let me know.


  7. Jon,
    Although this works great with an inside corner, an outside corner with the same 45 degree mullion will fail due to the curtain wall always wanting to justify at the outside edge of the mullion. In this instance, I had to build the corner mullion as one piece, apply it to one curtain wall corner, then delete the border mullion off of the adjoining one, disallow it's join, then stretch it until the glass touched the corner mullion. The issue with disallowing the join at the corner is the horizontal mullions will no longer clean up. Any solutions for a custom outside corner that will still allow both curtain walls to clean up?


  8. Hi Jon, have you been able to successfully utilize this method when you have a Captured and SSG in the same wall type?

  9. Could you send me an image/drawing of the condition that you're referring to?