How do I differentiate two different wall constructions in the same wall plane

If you have two different wall constructions (e.g. brick and wood) in the same wall plane then you can define the secondary (less prevalent) construction using a sub-surface.

To do this you should navigate down to the surface level to draw the sub-surface (in the same way as drawing windows, holes and doors). You can set the sub-surface construction on the Construction tab at any level you wish (building, block, zone, surface) and the data will be inherited by levels below it.

An alternative method when the split is a vertical one (e.g. on the left side is one construction and on the right side another) is to draw a very small “stub” partition to split the surface into 2. Then the constructions can be defined separately on each of the 2 resultant surfaces.