About the misleading year per inch drying rule

There and rules and then there are rules.

Jesse Cloud

I always thought of the "an inch a year to dry" rule as a rule of thumb. Wikipedia defines them as

"... a principle with broad application that is not intended to be strictly accurate or reliable for every situation. It refers to an easily learned and easily applied procedure or standard, based on practical experience rather than theory. "

For instance, a rule of thumb suggests that the gas cap and the exhaust pipe on a car are on different sides. Often not true, but true enough to inform a search for the gas cap on a rental car.

By the same token, there is no overwhelming need for a tenon to be one third the width of the workpiece, but its a reasonable starting assumption.

my point was that it is not

Bill Tindall, E.Tn.

I always thought of the "an inch a year to dry" rule as a rule of thumb.

"... a principle with broad application that is not intended to be strictly accurate or reliable for every situation.

The point I wanted to relay with data, supported by the Forest Products Lab data referenced, is that this folklore is not a good guide in any situation . The range is: under best conditions easily dried species can be dried to a usable 7% MC in 4 days while under poor drying conditions lumber will never reach a useable moisture content for complex furniture construction. Even the target has a range that makes this folklore useless. Is the lumber being dried to a point where it can be safely put in an accelerated drying environment for finishing the drying process? Is it being dried to use for furniture, or building a gate?

Bottom line: there is no substitute for understanding the drying process, what affects it, the ultimate target MC for an intended use and some way to know what the MC is to ensure the lumber is suitable for the intended use.

Anyone that thinks drying is trivial consider the following. When we sold lumber I was approached numerous times and offered a stack of lumber, usually walnut, "stored in the barn for XX years". Only once did I ever encounter lumber that was fit for us to sell. It was a stack of cedar, which is nearly impossible to screw up drying.

Under good drying conditions I dried lumber ready to experience accelerated drying conditions after 30-60 days. In a hot loft or makeshift kiln I could complete the drying process for poplar in a week. Left outside lumber never reaches useable MC around here.