Which area is the least likely entry point for sub termite infestation on a monolithic slab?

Hollow blocks are indeed the least likely entry point for subtermite infestations on a monolithic slab. This is primarily because subtermite activity is typically associated with soil and wood interactions. The structure of a hollow block, while it does contain voids, tends to be less accessible for termites compared to other entry points like cracks in the concrete, expansion joints, or utility entry points.

Cracks in concrete and expansion joints can create direct pathways for termites, allowing them easier access from the soil to the structural wood elements of a building. Utility entry points, particularly where pipes enter a building, can also provide openings through which termites can travel from the ground into the structure.

In contrast, hollow blocks do not provide a consistent and direct route into the interior of a building because the passageways are not as readily connected to the soil and are typically filled, limiting termite movement significantly. Hence, considering the nature of these entry points, hollow blocks present the least risk for subtermites gaining access to a monolithic slab structure.