I am working on a project where we are converting an existing garage (recent construction of the garage) to an ADU. We will be framing in a raised floor system just above the slab to accommodate the plumbing waste lines.

This is in Climate Zone 3 near the California Central Coast (Seaside CA). Although we don’t have what would normally be considered a humid climate there is a fairly high level of humidity all year long due to the marine layer.
Heat will be supplied by a ductless mini-split system. There will be a Panasonic ERV. The whole space is about 550 s.f. (2 bedroom 1 bath with laundry)

I don’t want passive ventilation like a crawl space. For fire prevention reasons if the space is ventilated it would be done mechanically. For insulation, rather than batts I am thinking about running a 1-1.5″ layer of eps on top of the slab and along the stem walls. This could be glued and screwed through battens.

Am I overthinking this detail? I don’t want to create an inaccessible science experiment.

Thanks,
Alan