Sawmill Byproducts and the Chip Flow

The streams at a glance

Chips are a product, not a residue

The most important thing to understand about sawmill chips is that they are specified, graded and sold like any other raw material. Pulp mills buy them by species, size distribution and cleanliness, and a chip that carries bark or grit is worth less because it damages pulp quality. Fuel chip quality is specified in the ISO 17225 series; pulpwood chips are traded under separate commercial specifications.

Two consequences follow.

First, the sawmill sits upstream of the pulp mill, not parallel to it. In regions with a large sawmilling sector, a pulp mill may take a substantial share of its fibre as purchased chips rather than as roundwood. Where that is the case, its wood supply becomes partly dependent on sawn timber demand, which is driven by construction rather than by pulp markets. When housing starts fall, sawmills cut shifts, chip supply tightens, and chip dependent mills must buy more roundwood at exactly the moment their own fibre cost rises. Fibre is the largest single cost item in pulp production, so the effect is material. This dependence is a regional characteristic, not a universal one: mills that run predominantly on roundwood or on recovered fibre are not exposed to it in the same way.

Second, chips are bulky to move. Loose chips are considerably less dense than stacked roundwood, so a chip trailer carries less wood per unit of load volume than a timber truck. Whether a chip load runs out of space or out of weight before it is full depends on moisture and equipment: fresh sawmill chips are wet and heavy enough that loads often reach the legal weight limit, while dry fuel chips typically fill the volume first. Either way, the haulage cost per tonne of fibre is higher for chips than for roundwood over the same distance, which is why chip flows by road tend to stay regional. It is not an absolute limit: large volumes of chips also cross oceans by ship, notably to pulp mills in East Asia.

Sawdust, shavings and bark

Sawdust volume is a direct function of blade thickness and the number of cuts. The saw removes wood as short particles rather than intact fibre bundles, so sawdust yields a short-fibred pulp with little reinforcing strength. Dedicated sawdust kraft lines were built from the 1960s onward, mainly in western Canada, and sawdust pulp was sold as a distinct grade, but the economics never matched chip-based lines and nearly all of that capacity has closed.

Shavings come from planing and are clean, dry and low density.

Bark is the lowest value stream, and in practice it is what dries the timber: a sawmill's kilns typically run on its own bark and sawdust. Where a district heating network is available, surplus heat is often sold into it, which turns a residue into a second revenue line. The same logic appears at pulp mills, see pulping byproducts.

Why we never add sawmill and pulp mill consumption together

The question arises because the sawmill sits upstream of the pulp mill: a large share of the chips a pulp mill consumes began as sawlogs at a sawmill, so the same wood shows up in the intake of both. WoodComp therefore reports consumption separated by assortment, with roundwood, chips and recovered wood in distinct columns, and never sums those columns into a single figure. The rule in full, with a worked example, is on the methodology page.