Thickened edge (turndown)
A deepened section at the perimeter or under a load-bearing line of a slab on grade, giving extra support without a separate footing pour.
What does thickened edge (turndown) mean?
Thickened edges carry concentrated loads from walls, columns, or vehicle wheels at slab edges where support is otherwise weakest. They usually contain additional longitudinal reinforcement and are formed by simply digging a deeper trench along the line before the pour. Where frost protection is required, a thickened edge alone may not extend deep enough.
In practice
Garage slabs, shed pads, and patio edges commonly get a turndown at the perimeter to keep the edge from breaking under wheel loads.