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Family reference planes and dimensions?

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    Family reference planes and dimensions?

    Is there anyone who can explain in detail (or knows of a good blogpost) how the reference planes in a family behave in a project?

    I have the bones of a window family created that I was testing and noticed when changing type (even just duplicating the window type) causes my dimensions to go crazy, for the most part they disassociate and in some case they jump around or are removed altogether.

    I've had a bit of a headache with dims and windows when we started a precast concrete setting out drawing (only showing the internal leaf of the wall), I learned that turning of the window category and placing dimensions the wall opening works fine until you move/edit/change the window which creating the opening. I put this down to the dim being to a point on a wall that happens to be snapable because theres an edge, I changed the view template and turned windows on and all subcategories off so that I could dimension to the windows reference planes instead of a random point on a wall.

    I'm now changing a few windows and the problem of dimensions disassociating is happening again but unsure why this is happening in views where I used the reference plane to snap the dims. All the windows were created based on the same family and in this instance all I'm doing is changing the height of the window and plan/elevation dims are not moving with it - I get errors simply duplicating the family without and change in geometry.

    In the family I have the ref planes defining the opeing in the all set to strong or left/right/top/bottom. I'm using 2x voids associated with their respective ref planes to create different internal and external opening sizes, which is probably where the issue is coming from?

    When you apply the dimensions in the Project you do need to notice whether Revit is indicating a reference or other part of the family (Status Bar and Tool Tip). If you apply the dimension to the edge of a form (shape handle) instead of a Reference then when you swap family types you may run into the problem you describe.


      A couple of other things to note:
      * If the Type you are swapping to has a parameter with an inappropriate value (such as a 0 or negative length) then you may get errors. Change the value to a sensible one and this may help.
      * When editing your family it is always best to lock you elements to reference planes and to dimension to those reference planes. Don't dimension straight to the elements. For a good list of family creation tips see the Best Practices table, section R2 in Australian & New Zealand Revit Standards | ANZRS


        I don't have any geometry in this window family, still working on that part, it's only got a nested family with model lines in it so elevations appear to have windows. Could the dimension be snapping onto ref planes in the nested family? The other thing I'm wondering is that I have 2x overlapping reference planes on each jamb/head/cill as I wanted the flexibility of controlling the internal and external opening independent of each other.

        Anthony: I only noticed this issue when I duplicated an existing window, I didn't change any of it's parameters when dims started to disassociate or delete. The only 0 value I have is for an offset which positions internal/external in the window in the wall. All geometry is locked to reference planes and those in turn are to dimensions with appropriate parameters

        Steve: on your blog, you have a couple dozen reference plane related families, have there been significant changes to how revit handles them since some were posted or are they all still as relevant as they were as far back as 2008?


          Ah...if a nested family is involved then the problem may be there instead. If you swap types and it involves changing the nested family too then there could be a break in the logic involved. For example, the nested family could be designed to flex from center out but in the host family it is constrained from a side toward the center. Flexing the width of the family will break the nested family's constraint logic because it expects to keep its center reference intact and move the left and right. All nested families must be built with same flexing logic and parameters that will be involved in different iterations.

          Re blog: Yes, most still relevant. The weak and strong behavior has changed a bit more recently but I believe I've written about that too.
          Last edited by Steve_Stafford; February 28, 2017, 08:00 PM.


            Hi Jozi: I understand that you may not have changed the parameters to zero values, but if they are set that way in the family then the errors can occur. Can be a good idea to check the values in the Family Editor and then reload Overwriting the existing values.

            And I agree with Steve, nesting adds to complexity.

            Steve: Good tip about the nested flexing logic. I was not aware of that one. Thanks. (BTW: I find it difficult to get past your anti-Robot when trying to comment on your blog posts.)


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