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Thread: Instance Parameters in Family Formulas.

  1. #1
    AUGI Addict Scott Hopkins's Avatar
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    Have you ever gotten this error message?

    "Can't define or use Instance Parameters in formulas."

    Why would you want to use an instance parameter in a formula you may ask? I am doing a custom home with all custom windows. Because the windows are custom they can be designed to any size I want. I created a window family with instance based height and width parameters so I can quickly adjust them in the model.

    Now my problem arises because I also want to create an area parameter so that I can include areas on the window schedule to show compliance with the Energy code. When I try to use the instance based parameters in the area formula I get the above error message.

    Am I missing something? Is there a reason why using instance parameters in formulas would cause the whole programming house of cards to fall down? Can anyone think of a work-around besides changing the window family back from an instance to a type based family?

  2. #2
    Autodesk Revit CSE
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    Default Re: Instance Parameters in Family Formulas.


    The way that I would approach getting the areas for the windows in your schedule is by using shared parameters.

    I created a shared parameter called area. (I am using a shared parameter because I want the area parameter to appear in my schedule)

    If you’re not familiar with shared parameters I would look at the tutorial in revit: select help / tutorials / project documents / Shared parameters and Multi-category Schedules.

    Open the family window.rvt within the family types, I have added the shared parameter area and then added formula to area (Width*Height). So for every fixed window type I will now have the area value for all window types.

    Load the family (window.rvt) into a project, create a window schedule.

    See attached zip file with family file Fixed_area.rfa shared parameter file window.txt and sample project window.rvt.

    Any other opinions / solutions?
    Attached Files Attached Files

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