Wall schedule doubles area for exterior + interior face

[qingdom]

Hello,

I am trying to list the interior and exterior surface area of a simple wall.

In this example first column shows the interior area and the second column the exterior area of the surface.

The third column is exposed area.

I need only one row because that would be true one 5.0 is enough for interior a 

nd the same row for 6.8 is enough.

How can i get rid of one row because is duplicating the surfaces this way?

Thank you