lofting

In underground mining, lofting is the process of installing horizontal timber beams, called lofts or lagging, across the top of mine workings to support the roof. These timbers rest on vertical or angled wooden props, called caps or stulls, that are themselves anchored to the pillars and walls of the excavation. The lofts distribute the weight of overlying rock across a wider area, preventing sudden collapse and giving miners safe passage below.

Lofting typically uses round pit props or hewn timbers sized between 15 and 30 centimetres in diameter, depending on the span and load. The timber runs longitudinally across the working, perpendicular to the direction of travel, spaced close enough that the combined load does not exceed the yield of each piece. In narrow seams or pillar-and-stall mines, lofting may be continuous along the entire length of the working; in larger chambers, it may be concentrated over main haulage roads where traffic and vibration pose the greatest risk.

The weakness of timber lofting lies in its degradation over time. Moisture, fungal rot, and insect damage reduce strength unpredictably, making periodic inspection and replacement essential. In long-lived workings, timbers must be checked monthly or more often depending on air quality and water seepage. A failed loft may cause rockfall over a large area, so the timber must be replaced while still sound, not after visible failure begins.

Lofting is distinct from stacking or pack walls, which are built vertically to support pillars or fill voids, and from roof bolting, a modern method using steel anchors drilled into rock. Before mechanical roof support, lofting was the standard method in coal and metalliferous mines worldwide. It remains common in older workings, particularly in countries where modernisation has been gradual, and it is still used in combination with other supports in some hard-rock mines where bolting alone is insufficient.