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560 | ChapTeR 13 Modeling Floors, Ceilings, and rooFs

be able to do that while editing the roof slope. Setting it here means specifying the way you
measure slopes for the entire project.

Figure 13.30
Format dialog box
for slopes

applying a Roof by extrusion
The roof by extrusion method is best applied for roof shapes that are generated by extrusion of
a profile, such as sawtooth roofs, barrel vaults, and waveform roofs. Like the roof-by-footprint
method, it is based on a sketch; however, the sketch that defines the shape of the roof is drawn in
elevation or section view (not in plan view) and is then extruded along the plan of the building
(see Figure 13.31).

Figure 13.31
an extruded
spline-shaped roof

Roofs by extrusion do not have an option to follow the building footprint, but that is often
needed to accommodate the requirements of the design. To accomplish this, you can use the
Vertical Opening tool to trim the edges of an extruded roof relative to the building outline.
Let’s briefly review the concept behind the Vertical Opening tool: You create a roof by
extrusion by defining a profile in elevation or 3D that is then extruded above the building.

c13.indd 560 05-05-2014 16:57:17