There was a house behind us where the builder did a runner.

Styrofoam is always used in the slab, but never in structural areas such as foundational footings to structural areas of the slab.

Particle Board is actually used as a component in Engineered beams because it has better torsional strength than plain wooden beams. You can get timber beams that are stronger than an engineered beam, but only from old-growth forest like Mountain Ash and Huon Pine. Steel beams are another option, but then you have more thermal issues.