A sectional elevation of a concrete roof is shown below (drawing is from the early 70s):
The roof slab is dimensioned as 6" thick with what appears to be 12" parapet wall with a 'Timber Insert'.
What is the purpose of this timber insert? Is it for fixing into?
My assumption is that it does not protrude beyond the face of the concrete i.e. it is not a sheet of timer forming a secondary roof.