Roof trusses can only be built after roof and ceiling planes are modeled. Select Build> Framing> Roof Truss, then click and drag in floor plan view within one or more roof planes to manually draw a roof truss.
Draw a truss as you would a CAD line, by dragging from the start of the truss to the end. The first truss can be drawn over a gable end wall or at the ridge end of a hip roof. The program shapes the truss so that it fits properly between the roof and ceiling planes.
One or both ends of the truss may be truncated if they come against existing roof trusses. If a truss is drawn across another truss, it terminates exactly on the surface of the existing truss, producing a girder truss.
If the roof or ceiling planes vary, so do the trusses. The ends of a truss expand or contract based on the roof and ceiling planes that define it.
Trusses can end on interior walls. You can draw a truss that partially crosses the building by starting and/or ending it within two feet (600mm) of the interior wall. The truss extends over the wall's main layer. Its end lines up with the main layer surface on the far side of the wall.
A roof truss can exist only between roof and ceiling planes. You cannot draw a roof truss above an area where you have unchecked Ceiling over this room in the Room Specification dialog. If this check box is cleared, you must manually draw a ceiling plane before a roof truss can be drawn over that area. See "Structure Tab".
The placement of webbing in a newly drawn truss is controlled by the Top Chord and Bottom Chord settings under Maximum Span on the Trusses tab of the Framing dialog. See "Trusses Tab".
If you intend to use roof trusses, select the Trusses (no birdsmouth) check box in the Build Roof dialog. When this is selected, the rafter depth that determines the roof plane thickness is taken from the Top Chord depth on the Trusses tab of the Framing dialog. If it is not checked, the roof plane thickness is determined by the rafter Depth setting on the Roof tab.
When Trusses (no birdsmouth) is selected and Raise Off Plate is zero, the bottom edge of the top chord bears on the top of the exterior supporting wall at the outside edge of the main layer. No birdsmouth is provided.
The truss top chord can be raised by entering the distance from the top plate to the bottom of the chord in Raise Off Plate in the Build Roof dialog.
If the program does not have enough information to model the trusses, a warning message displays. For example, a truss that is under the roof overhang but not over a ceiling produces this message:
"Roof and ceiling surfaces too close together or cannot be found, so cannot make truss."
The incorrect truss may still display in floor plan view with a label of the form "TR-*". If it does, it should be deleted or moved. See "Using the Edit Toolbar".
Attic trusses, a useful variation of roof trusses, can be drawn if a plan contains an attic area to either side and above an upstairs room, such as in a cape cod style home. The following is a typical cross section view of a building with attic trusses:
Certain conditions should be met before an attic truss can be built.
Once these conditions are met, a roof truss is ready to be designated as an attic truss.
edit button to display the Roof Truss Specification dialog. The final product can be scrutinized in a framing overview or as a CAD detail, see "Truss Details".
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