Wednesday, May 1, 2013

Creating Parametric T and F Clips

Several curtain wall systems, particularly in storefront  and strip window applications, use T and F clips to anchor the system.  The clips are fastened to the building structure along horizontal run of the curtain wall with the vertical members placed as a sleeve over the vertical protrusions of the clips.  This allows for vertical movement of the CW, as the building cycles through its normal changes throughout the year, but holds the CW in-place laterally.

This exercise follows the procedure to create a parametric F clip and a similar procedure can be used to create a parametric T clip as well.  By making the elements parametric, one family can be used for several different sized elements and fewer families are used in your models.  The basic procedure is: Create a profile, add dimensions, convert the dimensions to parameters, load the family into a model.  Here's how we'll do it:

1.  In Revit, click the Application Button (the R button) > New > Family to open the New Family-Select Template File dialog box.

2.  Select the Generic Model Face Based template then click Open.  This opens the design environment for a generic model that is oriented to a selected face in the Revit file.  This is chosen over the basic Generic Model template so that the clips can be used at either the top or bottom of the curtain wall.

3.  Make the Front view active.

4.  From the Home tab's Forms panel, click the Extrusion button.

5.  Draw the F clip in the view using the Line tool from the Draw panel of the Modify | Create Extrusion tab.  It isn't important that the lines are the correct length.  It is important though, that the lines are horizontal and vertical (except for the chamfers) and that the shape is closed without any overlapping lines.

6.  The chamfers need to stay consistent and this is handled better in sketch mode better than with the final, extruded element.  Zoom into the one of the chamfered ends.  Add a dimension starting from one vertical line near a chamfer then place your cursor over the opposite end of the chamfer and tap the Tab key until the blue, circular grip appears and select that point as the other point for the dimension.

7.  Click the lock icon, you may need to zoom out quite a bit to see this, to lock the dimension.  Repeat the process for the remaining seven dimensions that define the chamfers.

8.  Click the Finish Edit Mode button in the Mode panel to finish the sketch.  The dimensions near the chamfers will disappear; they are only visible and editable when editing the sketch.  If an error dialog appears, indicating that there are open ended lines or overlapping lines, click Continue and then address these issues before continuing.  Profiles must consist only of closed loops to create extrusions.

9.  In the Properties panel, set the Extrusion Start parameter to -0'  1 1/2" and the Extrusion End to 0'  1 1/2".  This will produce an extrusion that is 3" wide.

10.  To ensure that the model is stable when adjusting the parameters, we'll lock the vertical and horizontal perimeter lines to the horizontal reference face and vertical reference plane in the template file.  Select the extrusion then click on the lower horizontal line, not the blue triangle that appears, and drag it to the horizontal reference face, and then release it.  You don't want to drag the shape handle because that will change the shape of the profile. 

11.  To lock the profile in place, with the profile selected, click the Align tool in the Modify tab of the Modify | Extrusion panel, click the horizontal reference face then click the lowest horizontal line in the clip.  The lock icon appears allowing you to lock the profile line/shape handle to the reference plane.  Because the plane is pinned in place by default, it, and the shape handle will remain in place.  Click the lock icon.

12.  Repeat the step with the far left vertical line, locking it to the vertical reference plane.  If necessary, with the Move tool active, click the Constrain option on the Options Bar to prevent the extrusion from moving vertically.

13.  Dimension your extrusion but omit the dimension from the right perpendicular leg to the far right end of the clip.  You cannot have a parameter that defines the overall length and also one for every element that contributes to define that length - this would result in an error stating that the model would be over constrained.  By omitting that one parameter, the distance from the leg to the end of the clip is determined by the overall length minus the sum of the other elements' length parameters.

14.  In the Plan view, add a chain dimension from one edge to the reference plan to the other edge.  Select the dimension then click the EQ icon that appears to force the dimensions to maintain an equal value.  Add another dimension for the width of the extrusion.

15.  Now it's time to substitute dimensions with parameters.  Select the dimension that defines the overall length of the clip.  On the Options Bar, click the Label button, currently displaying <None> and choose <Add Parameter...>.

16.  This opens the Parameter Properties dialog box where the parameters are defined.  Make sure Family Parameter is selected as the parameter type, give the parameter a descriptive name and choose Instance as the type of data.  We prefer not to use spaces or hyphens in the Name field as they can result in errors when computing values in tables. 

17.  Click OK to create the parameter.  The parameter replaces the dimension in the view and has a default value the same as the dimension.

18.  Repeat steps 15-17 for the remaining dimensions, including the dimension in the Plan view.   Be sure to select Instance every time; each time the Parameter Properties dialog box is opened, the Type option is selected by default.  In this case, both legs are to maintain an equal length so a dimension is added to the other leg, then, with the dimension selected, the same parameter is selected from the drop-down list.  When that parameter is modified, the length of both legs will  change.

19.  Save your file then click the Load Into Project button to load it into a new or existing Revit file.

20.  In the Project Browser, select the clip type and drag it onto an existing face in the Revit file.  Move your cursor over another face to create a second clip; the base of the clip aligns automatically with the face that your cursor is over.

21.  Select each clip then adjust its parameter values, for each clip independently, in the Properties dialog box.

As you can see, with a little forethought and planning, you can easily make an adjustable, parametric clip that can meet many of your modeling needs.


  1. Hi, I would nest the Clip family in a Curtain Wall Panel family with all the necessary parameters for better workflow.

    1. Hi Kat,

      Thanks for the comment.
      In ideal situations, that would be a good solution, but we've found that the flexibility of leaving the clips outside of the panel or curtain wall families allows us to address design issues that arise. For example, a current project that we're working on has steps at the sill requiring that an F clip is used between the jambs where a T clip would normally be found. The curtain wall also has short segments that pivot 4 - 6 degrees at the verticals, making the verticals technically jambs in Revit while they're split verticals in the real world. This causes the orientation of the clip to split the difference between the orientation of the panels on either side.
      These, and many other, issues could be addressed with parameters within the clip families, but we try to avoid creating "super families" if a quicker, and often more efficient, method can suffice. If you have a situation where you've used clips nested in panel families, please send it to us and we'll cover it in a future post.



    2. Hello Jon, Could you please explain why you used a faced based family instead of the generic family in step #2?

  2. Hi Max,
    Thanks for the comment.

    The Generic Model Face Based family template gives us the ability to apply the clips to any surface in the models regardless of the orientation in the family.
    Using the Generic Model family template, you're presented with three reference planes that are used to orient the objects. Let's say that you orient the clip as you did in the exercise above, using the Generic Family template; the horizontal reference plane, as seen in the Front view is oriented relative to the horizotal reference planes in any of the elevation views in a model. You can rotate the clips (or use Flip Controls), in the Plan views, to change their orientations, while they would still sit on the same plane that they are currently located. You can not flip or rotate them in an elevation view so they could be used at the top of the curtain wall. A second family of clips would have to be created, oriented downward, be used at the top of the walls.
    Using the Generic Model Face Based family, you select the face that the model is to be applied to and its orientation changes relative to its orientation in the family. Using this method allows you to use the same family at both the top and botom of the curtain walls.