Instance Parameters in Family Formulas.

[Scott Hopkins]

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?

[jkendsersky]

Scott,

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?