Foundation Width from the Ground Up: A Bearing Rule for Stone Strip Footings

A stone wall is heavy enough that its foundation is a calculation, not a detail, yet footing widths are still commonly chosen as the wall's thickness plus a hand's breadth, whatever the ground. This paper builds the width from the ground up. Service loads are accumulated openly, per metre run, for four stated buildings — a single-storey stone cottage at 35.16 kN/m, a two-storey stone house at 71.82 kN/m, a single-storey outbuilding at 19.15 kN/m, and a two-storey house with a heavy slate roof at 80.7 kN/m — and divided by five stated soil bearing classes from soft clay at 50 kPa to compact gravel and weak rock at 400 kPa, with the stone footing's own weight (a 0.45 m deep stepped strip) included in the load rather than ignored. A stepped stone footing is also bounded geometrically: at least the wall thickness plus 0.30 m, at most the wall thickness plus 0.90 m. The rule originated here is the larger of the bearing width and the geometric minimum, refused where it exceeds the geometric maximum. On firm ground the geometry, not the soil, sets the width — the two-storey house needs only 0.75 m on stiff clay and everything firmer. On soft clay the bearing width takes over: 0.873 m for the cottage, and 1.783 m for the two-storey house and 2.003 m for the slate-roofed house, both beyond their stepped maxima of 1.35 m and 1.40 m. Soft clay is therefore named as the soil class on which a stepped stone strip footing cannot spread the load of a two-storey stone building enough, however it is stepped within the stated geometry. This study is simulated, not measured, and no footing described here has been load-tested.