As we’ve attempted to demonstrate in our first two articles (see Part 1 & 2), not all kiln dried lumber has the same moisture content. The numbers can vary significantly based on where the wood originates from and what the typical moisture content standards happen to be for at the location where the lumber was milled. European-run mills tend to dry their lumber to a moisture content level of 12-15% while many other mills would follow the North American standard of 6-8% moisture content for their kiln dried lumber.
Air Dry Each Pack of Lumber
Once the lumber is moisture tested, it should all end up getting air dried at the lumber yard no matter what its moisture content level turns out to be. The shipping containers that hold the lumber while it makes its way from the foreign mills to domestic lumber yards aren’t an ideal environment for wood by any means. Being in these undesirable conditions for weeks on end can cause changes to the lumber’s moisture content levels.
In the lumber yard, the lumber can sit in stacks that are up on blocks with proper spacing between boards to allow air flow. That way, any moisture that’s accumulated during the trip overseas will have time to dissipate. The lumber will also start to naturally lower in moisture content as it air dries and acclimates to a North American climate, which is typically much drier than the nation of origin of the exotic imported tropical hardwoods.
Each species of wood will take a different amount of time air drying at the lumber yard to reach satisfactory moisture content levels. The lumber should definitely not go straight from the shipping container to a kiln, as such a drastic and artificial drying process at this phase could be detrimental to the wood in the long run.
Drying can Offer Stability
Just as toasted bread is stiffer than bread that hasn’t been toasted, kiln dried lumber tends to have hardened cell walls that increase its level of stability. As moisture content levels lower below that 8% level, the wood will become significantly more stable for use in various applications. If you want wood that’s going to remain moisture resistant long after it comes out of the kiln, drying it to at least a level of 8% is a wise choice. Even in a coastal region, where the wood starts to gain moisture right after being kiln dried, it’s best to get that moisture level down to below 8% so it can gain that critical stabilization.
In our final article in this series, we’ll get into more detail about the advantages of wood that’s been kiln dried to reach North American standards for moisture content. When using lumber for construction, it’s always a good idea to take into account the amount of moisture the lumber is likely to encounter once it reaches its final destination. That consideration will play a big part in helping you to determine how low the moisture content ought to get in the first place before construction ever begins.