How do you distinguish between a trespasser who gets a footprint on your floor from a trespasser who burns down your house? You can't find it in physics and science. You find it in market value. A footprint on a floor doesn't make the house worthless. Burning it down does. But they're both just physical changes.
Market value is right, but I'd say it's not the value of the house that matters - it's the cost of restoring it to its original state. Cleaning up a footprint takes a few minutes; you could hire someone to do it for well under $100. Rebuilding a house takes months of effort and tons of material; it'll cost you tens of thousands of dollars to restore it, plus the cost of renting another home in the meantime. Those are the damages.