If you can’t export the height of a layer to a DXF file, it’s probably because you’ve got the wrong Column label set.

To export the height of a layer, make the layer the active layer then click on the feature whose height you would like to export. Then look at the name of the field  (in the bottom left hand side) with the height attribute you’d like to export (for example contours height might say “Elevation”). It is this field name that you must enter as the Column label when you tick on “Export Height (Z)” (So in the earlier contour example, the column label would be “Elevation” – without the quote marks).