A Lesson in Lumber

What do a violin, a floor and a greenhouse have in common? They’re all made of lumber milled from trees, but apart from that, little else.  But just as the uses for these wooden projects vary widely, so do the boards used to make them, which were milled from various parts of a range of tree species, using several different sawing methods.

Heartwood, as the name suggests, is cut from the center of the tree. It’s the most dense and therefore strongest part, and also most resistant to decay.

Sapwood comes from the outer portion of the tree, closest to the bark. Sapwood is younger, less dense and not as durable and resistant to decay than heartwood.

The Annual Growth Rings in a log can also tell a lot about how fast the tree has grown and how durable the boards will be. Widely spaced sapwood rings, for example, indicate a tree that has grown quickly and less durable, while closely spaced growth rings indicate slow growth and a denser, more durable lumber.

Knots develop where branches grow out from the trunk of a tree. As the tree grows, the branch remains attached to the pith in the middle of the tree, and a knot forms where the sapwood grows around the branch. While not a huge factor in simple projects like raised beds, knots should be avoided where the lumber will be used for load bearing structures like a greenhouse or even a chicken coop. Because knots shrink at a different rate than the surrounding wood, they often fall out, leaving a hole and weakening the lumber.

The method that lumber is cut from a log can also have a big impact on it’s durability and performance.

Plainsawn, also called flatsawn or "through-and-through." Is the most efficient way to yield boards from a log. The boards are cut in parallel, one right after another, from top to bottom, right through the pith of the log. Plainsawn is the fastest, easiest and most cost effective way to mill a log, can be used for the widest variety of trees, and is consequently the cut most commonly used in sawmills. By some estimates, over 90% of all logs are cut into boards using the plainsawn method.  

Unlike plainsawn boards, Quartersawn boards are cut at a 90 degree angle from the center of the tree. Quartersawn boards are easy to spot because the growth rings run at a right angle to the face of the board. This is referred in the industry as ‘radial grain’.  Why cut boards using the less efficient, more expensive  quartersawn method?

Quartersawn lumber has a much more uniform grain pattern making it ideal for high visibility projects like cabinets, floors, table legs, etc, and while plainsawn boards  have a tendency to shrink, swell, warp, twist, cup, or bend with changes in humidity, quartersawn lumber shows very little movement over time and is the first choice for fine furniture and instrument makers.

A board is referred to as quartersawn when it is cut radially from the center of a log, and as the angle of the cut becomes less perpendicular to the face of the board, the classification of the board goes from quartersawn to Riftsawn. Riftsawn boards are basically a byproduct of the quartersawing process, and  fall somewhere in between plainsawn and quartersawn in terms of durability, cost ; sort of the lumber equivalent of mid-grade gasoline. Riftsawing process produces a more durable board than plainsawn the plainsawn method, and a more affordable alternative to pricey quartersawn lumber.