Abstract: A prefabricated modular building system includes any of a deck, wall panel, and roof panel, each of which can, but need not always, include an ultra-high-performance concrete portion bonded to a foam portion to form a composite. The deck includes connection points for attachment of a stabilization structure and for releasable attachment of transport components such as a hitch and axle assemblies. The deck is fabricated off-site, and transportable to a delivery site where the transport components can be detached and the deck is placed on a foundation or piers. The stabilization structure can, in some implementations, form a complete building.