The Honest Load of a Green-Timber Lintel: Strength Loss and Creep in Unseasoned Wood

Builders frequently install a lintel green — freshly sawn, still wet — and then load it with the wall it was meant to carry, while the only capacity figures at hand come from tables for seasoned timber. This paper computes how much of the seasoned value must honestly be given up. The study is simulated, not measured, and no lintel described here has been load-tested. Using stated green-to-dry ratios for bending strength and stiffness, a stated factor of 3.0 on bending strength, a sag limit of span/250, and a stated creep model in which seasoned timber in dry service creeps by a factor of 0.60 while green timber drying under load creeps by a factor of 2.00, the governing allowable uniform load is computed for four sections, five openings, and three species classes, green and seasoned. Strength alone would require giving up 40.0% for the oak class, 34.0% for the pine class, and 30.0% for the light softwood class. Once lower green stiffness and the larger green creep are included, the loss grows substantially: a pine-class lintel of 100 mm by 200 mm over a 1.8 m opening retains only 42.6% of its seasoned governing load, falling from 21.95 kN/m seasoned to 9.36 kN/m green, a give-up of 57.4%; the corresponding oak-class lintel retains 40.5%, from 27.43 kN/m to 11.12 kN/m, a give-up of 59.5%. Under a fixed load of 4 kN/m the same pine lintel sags 1.03 mm at once when green and 3.08 mm in the long term, three times its initial sag, against 0.82 mm rising to 1.31 mm when seasoned. The derating schedule originated here is therefore simple to state and uncomfortable to ignore: for ordinary openings, plan a green lintel at roughly two-fifths of the seasoned table value, or enlarge the section, prop the wall until the timber has dried, or wait.