When I started milling lumber, Internet searches repeatedly said that you could air dry your boards using a rule of one year of drying time for each inch in the thickness of the lumber.
The one year per inch rule was everywhere on the Internet, and I followed the rule for my first year. Guess what? After a year, my lumber was nowhere near to being dry enough to use for building projects.
It wasn’t until I started researching a solar kiln and read the information from Virginia Tech that it all started making sense to me. In a single line on their website they made clear why my air drying wasn’t working like I had hoped. The line read…
While lumber can be air-dried, the humidity in most localities prevents the lumber from reaching the moisture content required for the stability needed for interior use.
Virginia Tech
In my part of Ohio the average daily relative humidity at 7 am is 80.3%. By 4 pm in the afternoon the average daily relative humidity drops to 57.3%. The wood is less inclined to release moisture when the surrounding air is already saturated.
I did a quick experiment by bringing some freshly milled walnut into the house. It was summer and it was hot and humid outside. The air conditioning inside the house kept the humidity low. The lumber when from around 40% moisture down to around 7% in about six weeks time.
I now have a selection of walnut, cherry, ad oak that is dry enough to use in some projects!