On the Section tab of the Wall: definition dialog, you can define parameters of a wall cross-section.
Specify parameters for each type of wall cross-section:
- Thickness
- Material
- Axis of wall definition
center line 
upper line 
lower line The methods of axis definition are illustrated schematically in the drawing below.
Center line selected
Upper line selected
Lower line selected
When defining a wall by means of the outer or inner line, you can specify an offset from the definition line. If the offset equals 0, the definition line coincides with the upper or lower line.
See also: How to define a wall if the distance differs from zero