On the close order of 11 feet/3.6 meters. But it depends on what you count as the root - at the fairing skin, the fuselage skin, or at the centerline joining (the internal wing box is slightly trapezoidal and thus a bit deeper at the join).
Coincidentally, just about exactly the same as the root thickness of the wing on the Hughes H-4 Hercules (Spruce Goose), although the H-4's airfoil was thicker, proportionally, and thus only had a root chord of 15.5 m.
Re: A380 chord vs A320 half span - quite correct, unless the A320 has sharklets.
Then its half-span is 0.2 meters longer than the 17.7m root chord of the A380.