Advanced tab on Model Options dialog.
For flat component blocks DesignBuilder uses the selection made here to decide which of the 2 largest surfaces of the component block is used in the simulation as a shading surface. Choose from:
1-Highest - the upper of the 2 largest surfaces is used.
2-Lowest - the lower of the 2 largest surfaces is used.
Definition of a flat component block
A component block is considered 'flat' when the 2 largest surfaces have the same area and constitute at least 95% of the total surface area of the component block.