since the bottom furring board touched the slab , must you use pressure treated wood?
You are correct. The International Residential Code (2012) postulates in Section R 317.1 that
R317.1 Location required.
Protection of wood and wood based products from decay shall be provided
in the following locations by the use of naturally durable wood or wood that is
preservative-treatedÂ Â ...
3. Sills and sleepers on a concrete or masonry slab that is in direct contact with
the ground unless separated from such slab by an impervious moisture barrier.
This obviously assumes you were asking about residential construction and a slab on the ground (basement or ground floor). That said, some municipalities don't allow furring strips on masonry floor at all. You should call the township / municipality Code Enforcement - they have the definitive authority here. Also would not hurt to specify that details conspicuously in the construction plans submitted with the permit application.
Â Excellent, knowledgeable response, much appreciated!