In OpenBuildings Designer Update 9 and later, the ‘Place Slab’ icon in the ‘Architectural’ and ‘Structural’ tabs only opens the ‘Place Compound Slab’ dialog. From there the legacy slabs cannot be placed.
To solve this issue there is a Key-in that can place legacy slabs in OpenBuildings Designer:
TFPLACE FORM 1SLABNEWDGEnter this key-in in the ‘Key-in’ dialog box.After that, you will see the ‘Place Slab’ dialog from where legacy slabs can be placed. Below is a video where the solution is demonstrated: