Editing a Joist Family to Avoid the "Can't make type" Error

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My first blog post here on the Revit Clinic was in reference to the "Can't make type..." error you may receive when attempting to place a joist: http://revitclinic.typepad.com/my_weblog/2009/03/cant-make-type-error-when-placing-joists-1.html

If you need to create a joist with a smaller span, you can edit the family. Let's use that same 24LH05 as an example again.

First, open the family.

Go to the Types dialog, and enter your desired Length. I'll use 13'-6" as an example.

Click OK. You should see two errors:

Cancel out of the warning dialog. The first error is the key in this scenario - changing the length is making the IntPanelArrayNum parameter invalid. From here you need to understand what the parameters in the family are doing so you know how to change them.

Scroll down to the Other section in the Family Types dialog. When you decrease the length, where do you want the length to be taken from? From the image in the first blog post,you'll see you have control over 3 parts of the joist: the End Panels, the Internal Panels, and the Variable Panels. The Variable Panels are driven by the End and Internal Panels, so the best way to approach it is by working with the End and Internal ones.

If you want the length taken out of the End Panels, you'll need to adjust the End Panel formula. Right now the width of the End Panels are 1.5x the Depth of the joist. If you let them be 1x the Depth, you'll be able to make the joist shorter.

If you want the length taken out of the Internal Panels, you'll need to adjust the IntPanelWidth parameter. Right now it says that the minimum width they can be is 2x the Depth. If you change it to 1.5x or 1x the Depth, they will be able to be shorter.