It’s not what you do, it’s how you do it what makes the difference!
Kiln-drying boxed heart timber in large sizes to 15% moisture content in the core? It’s possible when you use the right technique.
Large timber sizes usually only come in boxed heart. Here at Daizen we use a “stress-relief-cut” on a non-exposed side of the timber to release the tension, that can get created during the drying process, trough this cut. This clean cut that goes all the way to the heart of the beam will eventually open up during drying and prevents the exposed beam sides from large checking.
An important benefit of the technique is that the change in the timber dimension happens already during the drying process. After the finish planing the timber size stays unchanged.
The picture below shows a 16” x 16” boxed heart post. The originally 1/4 inch cut opened up to nearly 1”, released all the tension here. The other sides ended up with no or only minor checking. The cut is getting covered by a joining stick-frame wall member.
The second picture shows a 9” x 20” beam with an 10” relief cut into the heart before it goes into the kiln. The cut will be later on top of the plate, non visible.