Residue streams: what leaves the mill besides boards

Why residues matter

A sawmill sells boards, but a large part of every log leaves the mill as something else. A Finnish review (Finland, 2019) reports that side-streams make up about 15% of revenue for large and medium sawmills, and that 30-55% of roundwood ends up as side-streams depending on the final product. Treat 15% as an order of magnitude, not a benchmark for your own mill.

The five residue families

• Bark: removed at the debarker. Its quantity depends mostly on log diameter and species, not on the sawing pattern. Usually wet and variable.
• Sawdust: produced by the saw kerf. It depends on blade thickness, number of cuts and product mix.
• Chips: made from slabs and edgings, or directly by chipper-canter lines. Clean, bark-free chips have the highest value (pulp, some boards).
• Planer shavings: produced in planing and moulding, therefore dry. They go to pellets, briquettes, panels and bedding.
• Offcuts, slabs, trimmings, sanding dust: mixed streams; some are chipped, sanding dust is a fine dry fraction.

Published shares differ, and they are not additive

Shares are expressed on different bases (solid volume, bulk volume, dry mass), for different species and mill types. The table shows what the portal's article could verify.

Add the upper ends of the Finnish column: 54 + 32 + 15 + 12 = 113. A real log cannot give 113%, which shows that the ranges mix volume bases. Never add figures from different sources. The practical reading is simple: sawnwood is roughly half of the log, and the rest is a bundle of co-products dominated by chips.

A simulated Finnish case (one stand, a simulator, not mill measurements) gives about 53% sawn timber, 28% chips and 15% sawdust of log volume. These add to 96%; the source does not explain the remaining 4%.

Two more data points

• Slovakia, 2020 (survey of 57 of 177 contacted companies): by-products were 42.1% of sawmill production. National totals were 477,392 m3 of chips, 254,600 m3 of sawdust, 180,650 m3 of cut-offs, slabs and edge boards, 16,853 m3 of bark and 14,205 m3 of shavings. The very low bark volume is probably a reporting artefact, because many mills do not record bark separately (interpretation).
• New Brunswick, Canada, hardwood, 2022 (two mills, rough green lumber): cubic lumber recovery is low because 60% of the harvested logs were pulpwood grade. The volume conversion is 36.4%, which means about 2.75 m3 of logs per m3 of lumber. In oven-dry mass, 1,461 kg of logs gave 532 kg of lumber. The rest left as co-products, by mass roughly 47% chips, 8% sawdust and 9% bark, against 36% lumber. This is North American hardwood and must not be transferred directly to a European softwood mill.

Worked example: how many logs, how many chips?

A hardwood mill like the New Brunswick case wants to make 3,000 m3 of rough green lumber.

1. Log volume needed: 3,000 / 0.364 = 8,242 m3, or about 3,000 x 2.75 = 8,250 m3.
2. A mill receiving 2,000 t of oven-dry logs with the same mass pattern produces about 2,000 x 0.47 = 940 t of chips and 2,000 x 0.09 = 180 t of bark.

Always state the basis (volume or mass, wet or oven-dry) next to the number.

Checklist: before you quote a residue share

• Is it volume or mass? Solid or bulk? Wet or oven-dry?
• Are logs measured over or under bark?
• Is the lumber rough green, dried or planed?
• Which species, region and year? Is it a mill measurement or a simulation?
• Does the mill itself record bark, shavings and sanding dust separately?

Because the literature is not harmonised, the portal's article concludes that any benchmark should rest on the mill's own measured mass balance, not on literature averages.

Key points

• Residues are bark, sawdust, chips, planer shavings and mixed offcuts; side-streams were about 15% of revenue for large and medium Finnish sawmills (order of magnitude).
• Sawnwood is roughly half of the log in Finnish figures; chips are the largest co-product.
• Published shares use different bases and cannot be added across sources (the Finnish upper ends sum to 113%).
• Lumber recovery is species- and log-quality-dependent: 36.4% in the New Brunswick hardwood case, about 2.75 m3 of logs per m3 of lumber.
• Always record the basis: volume or mass, wet or dry, over or under bark.