Truss Base

A Truss Base defines the boundary separating the tops of normal roof trusses and valley fill roof trusses that lie across and above them.

To define a truss base, select Build> Roof> Truss Base .

. Create the truss base as you would a roof plane or ceiling plane. No overhang is produced.

The truss base is similar to a roof plane in its creation and definition. If you select it and click the Open Object

edit button, the Truss Base Specification dialog will open. See "Truss Base Specification Dialog".

Truss bases are used to create valley fill trusses. The best way to understand valley fill trusses is the example of an "L" shaped house with a gable roof. The wider wing of this house is trussed through from end to end with normal trusses. Starting at its outside end, the narrow wing is trussed with normal trusses until the wider wing is reached.

Where the valley begins, valley fill trusses are placed over the top of the main roof until the peak of the narrow wing's roof is reached.

Only three valley fill trusses, TR-2, TR-3, and TR-4, are used in the following example.

The truss base defines the footprint of the valley fill trusses on the main roof. In order to model the trusses correctly, you must draw the truss base.

If drawn correctly, a truss base should be in the same plane with, and its baseline should be collinear with its surrounding roof plane.

The purpose of a truss base is to form a boundary separating normal trusses below from the valley fill trusses above. You already know that trusses are built between roof planes and ceiling planes. A truss passing through a truss base is placed below the plane of the base if it is more perpendicular to the baseline of the truss base. It is built above the plane of the base if it is more parallel to the baseline.

To create a truss base

Create an L-shaped house with the roof plan shown below.

The triangular area of overlap between the main roof and the gable must be defined as a Truss Base.

Choose Build> Roof> Truss Base

, then draw a baseline along the outside edge of the wall from valley to valley.

Move the pointer and click on the point where the gable intersects the main roof.

The program creates a rectangular truss base. Use its edit handles to change its shape as needed.

Draw the first truss.

Select the truss and click the Multiple Copy tool.

Drag from the Move handle to create copies at the defined intervals.

The trusses placed for the main roof generate right through the truss base, stopping on top of the wall, eliminating the overhang in that area.

When the main trusses are in place, draw the first truss on the gable in a position where it will be full length.

Select the truss and click the Multiple Copy edit button on the Edit toolbar.

Drag the normal truss up into the truss base. Copies of the truss appear as you drag the pointer.


Note: Trusses that run perpendicular to the baseline of a Truss Base go under the Truss Base. Trusses that run parallel to the baseline of the Truss Base climb the Truss Base.

Release the mouse button, the copies are clipped by the truss base. Note the three valley trusses that are darker in the diagram below.