What is air dried oak?

Let’s Start From The Beginning

As an oak tree grows, it naturally draws water and nutrients from the ground.

At the point at which a tree is felled, this water stops entering the tree and will over time, become seasoned or air dried oak.

This period of time is usually amounts to years and in most cases, the oak tree is cut into manageable sections within weeks. This oak is known as ‘green’ oak.

Moisture Content

The key in determining the definition of air dried oak, is the amount of time the oak is given after been felled; normally more than one year. The moisture content (MC) could be as high as 70% in the early weeks and months.

During this time, the MC of the oak reduces slowly as the oak naturally dries out. This is a slow process and as a guide, a section of oak will dry at approximately 25mm (one inch) per year.

Another common phrase for air dried oak is seasoned oak; i.e. seasoned for a length of time. The longer the oak is left to naturally dry, the lower the MC will be. Depending on the size of oak beam produced, it could be over 5 years before the oak has an acceptable MC for oak framing; especially when glazing is involved.

The Air Drying Process

The drying process is relatively simple.

The oak beams are normally ‘sticked’ and ‘stacked’. This means a small spacer is placed between the oak beams allowing air to pass between them.

Not always, but air-dried oak can be found sheltered from the weather in covered but open sided barn-like structures.

During this drying process the oak ages, slightly discolours, shrinks and produces natural characterful cracks.

For more information on air dried oak, please click this Trada link about European oak.

Air Dried Oak Products

The way to consider if a product uses kiln dried or air dried oak is to look at oaks dimensions.

Most thin and medium boards are kiln dried and are used in products such as oak doors, engineered oak flooring and windows.

Larger timbers that create buildings, porches and structures use air dried oak.

Note, not all companies use seasoned oak; they use green oak.