Sawn timber in the yard: stacking, air drying and weight

Once logs are sawn, the cheapest logistics operation is often to let the yard remove water. The portal's air-drying and kiln articles supply the rules, almost all from North American sources, so read the numbers as examples. The economics article adds the cost side. Together they show how stacking, roofing and waiting decide the condition and the weight of what you eventually ship.

Why remove water before shipping

The USDA Dry Kiln Operator's Manual states that removing water reduces weight and therefore shipping and handling cost, and that protecting dried wood from re-wetting limits decay. It also says fungi cannot grow at a moisture content of 20% or lower and that temperatures above about 66 degrees C are lethal to them. Moisture content (MC) here is on the dry basis: water mass over oven-dry mass.

Worked example (own calculation). The New Brunswick hardwood study reports an average green MC of 67% and a green specific gravity of 0.532. If specific gravity is oven-dry mass per green volume, one m3 of green wood holds 532 kg of dry wood and 0.67 x 532 = 356 kg of water, a green mass of about 888 kg. Dried to 20% MC (and ignoring shrinkage) it weighs 1.20 x 532 = 638 kg. The water lost is 250 kg, about 28% of the green weight. This is one hardwood study; softwoods and other species differ.

Invented payload example. Assume a vehicle with a 26 tonne cargo limit (an invented figure, not a regulation). On weight alone it could carry 26 / 0.888 = 29.3 m3 of the green wood or 26 / 0.638 = 40.7 m3 of the dried wood, if volume space allows. Real trucks are often limited by volume or axle load, so this shows the direction of the effect, not a legal payload.

Air-drying yard rules (US sources)

• Foundation: FPL-GTR-117 says the foundation should be reasonably high, 460 to 610 mm. Stacks must stay off the ground because drying is slower there.
• Stickers: sources give thicknesses of about 19 to 25 mm and spacing of 12 to 24 inches (roughly 0.3 to 0.6 m), with 24 inches safe only if vertical alignment is perfect (Wengert, 2013). Stickers shorter than the pile width increase cupping and warp; they should be flush at the ends. No European sticker norm was opened.
• Pile size: widths of about 1 to 2.4 m and heights of about 1.2 to 4.6 m, up to 9 m with bolsters. Hand-stacked piles should not exceed about 1.8 m in width without flues.
• Top weight: 60 pounds per square foot or more for air drying, and Wisconsin DNR asks for at least 50. Own conversion: 50 and 60 pounds per square foot are about 244 and 293 kg/m2.
• Time to stack: stack within 2 to 3 days of sawing (Wisconsin DNR), and leave 6 inches between roof and stack.
• Alleys: at least 24 inches (about 0.6 m) between stacks, and stacks parallel to prevailing winds.

Roofs, end coating and sheds

FPL-GTR-117 says roofs should project about 0.3 m at both ends of a level pile, and warns that rain penetrating a pile can cause sticker stain. It recommends moisture-resistant coatings on freshly trimmed green end grain before checking starts; thin coats are insufficient, and a gallon covers roughly 100 square feet (about 9 m2 per 3.8 litres). In a Polish beech trial, 12% of items showed warping, twisting or end checks deeper than 15 mm after summer drying, attributed to maxima around 30 degrees C and strong sunlight.

Oklahoma State (2017) lists 1-inch maple, cherry and oak at 130, 150 and 200 days in a roofed outdoor pile, against 100, 110 and 120 days in an unheated shed and 30, 70 and 60 days in a heated shed. Own calculation: the unheated shed saves 23% of the maple days (100 against 130), and the heated shed 77% (30 against 130). Each step of control cuts days, which cuts inventory.

Controls that follow

Record the stacking date for each pile, set a cut-off date after which piles go to a pre-dryer or kiln instead of waiting out the winter, roof every pile, and keep stickers dry. A pre-dryer beats a yard where winters or wet seasons dominate, where stain-prone species or warm wet springs threaten, where land is scarce or where the kiln is the bottleneck.

Key points

• Drying cuts weight: in one hardwood study about 250 kg per m3 (28% of green weight) between 67% and 20% MC, own calculation.
• Weight gain from dryness helps only if the truck is weight-limited; check volume and axle limits.
• Yard rules (foundation, stickers, top weight, roofs, end coating) are mostly US figures; verify locally.
• Sheds and heat cut drying days: unheated shed 100 against 130 days for maple (Oklahoma).
• Record stacking dates and set a cut-off for pre-dryer or kiln.