This page describes DesignBuilder pitched roof geometry generation with reference an example roof created by drawing a rectangular perimeter with an offset of 0.3m and an external wall thickness of 0.25m:
Roof perimeter blocks are created behind the scenes by first generating a conventional plan extrusion using the current external wall thickness and then generating the roof inner profile topology from the resulting block outer perimeter:
The roof geometry is created as if a stub wall existed from the original extrusion, cut to fit within the roof space and on top of which the roof assembly sits:
The resulting roof block is composed of a polyhedron representing the inner zone, which is created from the original inner block perimeter and is cut to fit within the roof space and a number of slabs that represent the actual roof construction. The roof slabs are generated from the inner roof profile and an outer profile created using the roof construction thickness.
DesignBuilder automatically generates overhangs for Pitched roof block types using EnergyPlus shading devices. The diagram below shows EnergyPlus DXF output of the building model generated using the above data. It shows the overhangs in grey.
