It is a common misconception that all wood resting on concrete must be pressure treated.
PROTECTION AGAINST DECAY
R319.1 Location required. Protection from decay shall be
provided in the following locations by the use of naturally
durable wood or wood that is preservative treated in accordance
with AWPA U1 for the species, product, preservative
and end use. Preservatives shall be listed in Section 4 of
Wood joists or the bottom of a wood structural floor when closer than 18 inches (457 mm) or wood girders
when closer than 12 inches (305 mm) to the exposed
ground in crawl spaces or unexcavated area located
within the periphery of the building foundation.
All wood framing members that rest on concrete or
masonry exterior foundation walls and are less than 8
inches (203 mm) from the exposed ground.
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.
The ends of wood girders entering exterior masonry or concrete
walls having clearances of less than 0.5 inch (12.7
mm) on tops, sides and ends.
Wood siding, sheathing and wall framing on the exterior
of a building having a clearance of less than 6 inches (152
mm) from the ground.
Wood structural members supporting moisture-permeable
floors or roofs that are exposed to the weather, such
as concrete or masonry slabs, unless separated from such
floors or roofs by an impervious moisture barrier.
Wood furring strips or other wood framing members
attached directly to the interior of exterior masonry walls
or concrete walls below grade except where an approved
vapor retarder is applied between the wall and the furring
strips or framing members.
Not asking about PT. I’m only looking for a reference to a shim, barrier, material of some sort which is required to separate masonry and non-decay resistant wood beams or girders at their bearing point. I admit, I’m assuming it’s there but perhaps it’s not.
What I cited is the criteria for decay resistance. There is no reference to a requirement for shims at all.
There is also this:
“R319.1.2 Ground contact. All wood in contact with the
ground, embedded in concrete in direct contact with the
ground or embedded in concrete exposed to the weather that
supports permanent structures intended for human occupancy
shall be approved pressure-preservative-treated
wood suitable for ground contact use, except untreated
wood may be used where entirely below groundwater level
or continuously submerged in fresh water.”