Strip footings

How it works

The strip footing runs beneath the walls and spreads the line load of the wall onto the ground. Its width follows from the pressure permissible on the ground; its depth is generally set by the frost depth.

What is particular to light gauge steel

Bearing capacity is rarely the bottleneck

Because the line load is small, the width needed is small. So the size of the strip is often a question of buildability rather than structure: too narrow a footing is hard to form and shutter.

Uplift, though, is a question

Tension arises at the ends of the shear walls and from wind suction. The weight of the strip offsets it in part, but the anchorage still has to be designed. Hold-down anchorage.

The floor is a separate structure

With strip footings the floor is generally an independent, ground-bearing structure. That determines the build-up and the insulation too.

What has to be solved at the junction

Damp-proofing beneath the bottom track. Damp-proofing at the base.
Breaking the thermal bridge where the foundation meets the wall. Slab edge.
A flat surface and accurate setting out to receive the panels.
The position of the hold-downs — cast in or post-installed.

When it is a good choice

known ground of good bearing capacity,
a level site,
where the floor is ground-bearing anyway,
where the contractor’s routine suits it.

When it is less so

on weak or uneven ground, where a raft is more even,
where the volume of earthworks would be unjustified,
where the water table is high,
if the building is to go up fast without wet trades — there ground screws are competitive.

The point
Section titled “The point”

The strip footing is simple and well known. For a light structure its size does not follow from the load — but the junction details need the same care.