If you select number are your result type, you get sorting only by the numeric values in the combined field. If you select text as the result type, the system sorts by text sorting rules (alphabetical order).
It would appear that neither option works for you. I would suggest that you not sort on either field, but sort on the separate building and room fields used in your calculation so that you can get both alphabetical and numeric sorting for your report.
Thanks for the reply. I had to add those two fields (building and room) to the layout and then sort, but that worked. I like View as List better than View as Table. Is there a way to now hide these two fields in List View? I know how to do it in Table View, but not List View.
You do not need to add a field to a layout in order to use it in a sort order.
How right you are. Duh.