QUESTION:

When a surface is inside a building -- a partition or ceiling/floor -- which side is considered the internal or external such that the colour/reflectance value can be set correctly ?

ANSWER:

If you go to the Display Menu in ECOTECT and choose the Surface Normals option, this will help you to determine the "inside" vs. the "outside" of a surface.

The direction that an objects surface normal points is always considered the outside or external surface. It doesn't matter what the object is, or if it is actually "inside" a zone.