A sawmill is a wet, dusty building full of moving wood
A sawmill receives logs, cuts them into lumber, and dries and grades the result. A plywood plant peels logs into veneer, dries it, glues it and presses it into panels.
Both are timber buildings in the sense that the product is wood, and both share the same two problems: water and sawdust.
Green timber is mostly water
Freshly felled logs contain a large proportion of water by weight, and that water leaves the log on the saw floor. It runs onto the slab, it evaporates into the air, and it condenses on the underside of a cold roof.
A sawmill hall is therefore humid at the top and wet at the bottom, which is the same corrosion profile as a wet food process. The difference is that the material being processed is itself combustible, so the usual protection strategy has to be chosen carefully.
Sawdust is fuel, and it is generated continuously
Cutting produces sawdust and chips at a high rate. Most mills sell or burn the residue, which means it is stored in quantity, often under the same roof as the saws.
That storage is a fire load next to an ignition source. A wall between the production hall and the residue store is the cheapest fire engineering available, and it also stops dust migrating into a space nobody cleans.
Sawdust also settles in roof profiles where it holds moisture against the steel. The roof over a saw floor is the part of the building that ages fastest, and it ages from the inside.
A plywood press is a heavy, hot machine
Hot presses are large, heavy and they operate at temperature. The press frame carries its own load, but the floor beneath it has to be flat and stable, and the press house has to handle the heat it releases.
Veneer dryers are the other heat source: they are large, they run continuously, and they discharge moisture and hot air. The dryer house is effectively a drying building with a roof over it, and its ventilation is a process requirement rather than a comfort one.
Log handling is the site's biggest structure
Log yards, debarking, and the infeed to the saw line involve heavy mobile equipment and large stockpiles. The building starts after the log handling, and the interface between the yard and the infeed is where the layout is won or lost.
A log yard that is not drained turns into a mud site within a season, and the mud is carried into the mill on tracks and tyres.
What I want before drawings
- The process flow and where green timber, dry timber and residue are stored.
- Whether the residue is stored under cover, and where.
- The press and dryer sizes, masses and heat release.
- The log handling method and the yard layout.
- Whether a dust hazard assessment exists for the sanding and trimming areas.
- The wind speed for the site in km/h from the applicable local code, not a round number.
Timber plants are usually built where the resource is, which means remote sites and local contractors. Simple, buildable details matter more here than an optimised frame.
Written by Johnny Joe, who advises owners and project managers in Africa and South America on steel buildings. If this decision is live on a project, send the layout and the constraint that worries you and I will tell you what it changes.
Related: a plant that generates its own fuel · a dry product with a fire load · separating a fire load · crane rails in a production hall
