Ground screw sizes, spacing and foundation design

Size is more than length

Ground screws vary in length, shaft and helix geometry, head connection and intended application. Choosing by length alone ignores the ground, load and structure above.

The final depth that can be achieved also depends on the installation response and any obstructions encountered.

Spacing follows the structure

Screw positions should coordinate with the structural base, support points, spans, openings and load paths. A generic square grid may not suit the building above it.

Closer spacing is not automatically a substitute for the correct screw or an appropriate structural layout.

Information needed for design

• Structure type, dimensions and base or frame arrangement.
• Relevant design loads and concentrated support points.
• Ground information and any known fill, services or obstructions.
• Access, levels, trees, boundaries and sequencing constraints.
• Connection, tolerance and handover requirements.