Creating a Parallel Chord Roof Truss

Reference Number: KB-03165

Last Modified: June 22, 2022

The information in this article applies to:

QUESTION

How do I create a parallel chord roof truss?

ANSWER

In a parallel chord truss, the top and bottom chords of the truss follow the same slope. In Chief Architect, roof trusses generate between roof and ceiling planes, so to create these types of roof trusses, a vaulted ceiling must be created with the same slope as the roof directly above it.

To build the structure and roof

Open the plan that you would like to create parallel chord roof trusses within.

In this example, a simple 20' x 30' rectangular plan is used.
If you haven't established a gable roof yet, use the Select Objects tool to select the walls that you would like to make gable walls, then click the Open Object edit button.

In this example, the left and right walls were selected and opened to specification.
On the Roof panel of the Wall Specification dialog, select the Full Gable Wall option, then click OK.

Note: You can also use the Change to Gable Wall(s) edit tool to convert hip walls to gable walls without having to open the Wall Specification dialog.
Select Build> Roof> Build Roof and on the Roof panel of the Build Roof dialog that displays:
- Check Auto Rebuild Roofs.
- Set the desired Pitch (in 12).
  
  In this example, a 6" in 12 pitch is used.
- Check the Trusses (no Birdsmouth) box.
- Set the desired Raise/Lower From Ceiling Height.
  
  In this example, 18" is used. This will raise the roof 18" from the vaulted ceiling, allowing space for the parallel chord trusses.
- Click OK to build the roof.

To build the ceiling

Using the Select Objects tool, click in the room that will have a vaulted ceiling to select it, then click the Open Object edit button.
On the Structure panel of the Room Specification dialog, uncheck Flat Ceiling Over This Room, then click OK.
To make it easier to draw ceiling planes, select Tools> Layer Settings> Display Options and in the Layer Display Options dialog for the active layer set:
- Scroll down to the "Roof Planes" layer and remove the check in the Disp column or from the Display checkbox.
- Click OK to close the dialog and turn off the display of the roof planes in the plan.
Select Build> Roof> Ceiling Plane from the menu.
- Click and drag a baseline along the outside of a wall defining the room that will have a vaulted ceiling.
- For best results, the baseline should be along the outside edge of the framing layer.
- When the baseline is complete, click once in the room to set the ceiling planes ridge.
Click on the ceiling plane to select it, then use the edit handles that display to stretch it across the room to the inside surfaces of the gable walls.
With the ceiling plane still selected, click the Open Object edit button and on the General panel of the Ceiling Plane Specification dialog:
- Specify the Pitch to match the roof that was generated in the section above. If the Pitch field is grayed out, select the Lock radio button next to Height Inside Wall.
  
  In this example, 6" in 12 is used.
- Now lock the Pitch and set the Height Inside Wall value to your preference.
  
  In this example, a value of 109 1/8" is specified, which matches the room's height.
- Click OK to close the dialog and apply the change.
Repeat steps 4 through 6 to create a second ceiling plane opposite the first.
Click on the ridge edge of one of the ceiling planes.
Click the Join Roof Planes edit button then click the ridge edge of the other ceiling plane.
The two ceiling planes will join along the selected edges.

If you wish, you can toggle the display of the "Roof Planes" layer back on using the Layer Display Options dialog or the Active Layer Display Options (ALDO) side window.

To create parallel chord roof trusses

With both the ceiling and roof planes in place, you can now create roof trusses.

Select Build> Framing> Roof Truss from the menu.
Click and drag to draw a roof truss perpendicular to the ridge line of the roof and ceiling planes.
Click and drag to draw a roof truss perpendicular to the ridge line of the roof and ceiling planes.
With the truss in place, select it, then click the Open Object edit tool.
On the General panel of the Roof Truss Specification dialog that displays, change the Maximum Horizontal Span for both the Top and Bottom Chords, then click OK.

In this example, 40" is specified for both.
With the truss still selected, click the Multiple Copy edit button, then click the Multiple Copy Interval button to open the Multiple Copy dialog. Verify that Offset Between Copies When Dragging is selected and that the Primary Offset specified for All Trusses equals the desired O.C. truss spacing, then click OK.

In this example, the default Primary Offset value of 24" is used.

Note: Multiple Copy is not available in Home Designer Pro. Instead, use the Transform/Replicate edit tool. As an example, if you wanted to create 6 copies all separated a certain distance from each other, you would check the Copy box, set the Number of Copies to 6, then check the option for Move and set the X Delta to be 24". Negative values can also be set for each of the deltas if needed.
Hover over the main Move edit handle on the truss until you see the Multiple Copy cursor display, then click and drag across the structure to create copies 24" apart.

The trusses located on each end of the structure will be a full size trusses. If you wish to have end trusses instead, group select the trusses on each end, open them up to specification, check the "End Truss" and "Force Truss Rebuild" boxes, then click OK.
Create a Framing Overview to see the results.