04 Apr 2023

Understanding the Difference Between Green Oak and Air-dried Oak

There is something wonderfully rustic and evocative about the natural charm and character of oak, which, when expertly constructed, helps to exude English quality craftsmanship, says Karen Bell, Sales Director at David Salisbury.


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Popularised as a building material in Medieval England and well used in those times for shipbuilding, this immensely strong and durable timber is ideally suited to constructing homes. Indeed, many timber-framed homes built in those times still exist to this day.

In recent years, oak-framed orangeries and garden rooms have become increasingly popular, offering a natural charm and beauty you can only find with solid wood.

These properties are helping to accelerate the trend for replacing an old, run-down uPVC conservatory (typically built in the 1980s and ‘90s) with a new oak-framed orangery or garden room, packed full of the latest building and glazing technologies to provide luxurious all-year-round use.

Whilst the comfort and specifications of these oak extensions have significantly evolved over the years, choosing the right quality oak is essential for the success of any such building project.

Quality of materials is clearly just as important as ever, but not everyone is aware of the different types of oak available, or the implications of using each. In this article, we will take a look at some different examples and their suitability for use in different applications.

What is green oak or air-dried oak?

Both green oak and air-dried (or seasoned) oak are sourced from the species of an oak tree. The fundamental difference is the level of moisture held in each specific piece of timber, which is determined by how long the tree has been felled and subsequently stored.

Both types of oak have their advantages and disadvantages, which are vital for homeowners to understand if they are considering investing in a new oak-framed building.

Green oak

Green oak is newly felled and sawn and is sometimes referred to as wet oak. This term is used to describe unseasoned sawn timber, which has usually been cut within three to 18 months of being felled and has a moisture content of between 30 to 80%.

The use of the term green is, therefore, not to do with the colour of the oak, but actually its relative freshness and, critically, proportion of moisture.

Relatively easy to machine, this is an ideal timber for the frame construction of barns, garages and outbuildings where shrinkage and movement are not detrimental.

As it dries out over time, moisture loss can cause shrinkage, warping, twisting, fissures and shakes. Whilst all of these are entirely natural, any such significant movement within an oak frame housing windows or glazing can clearly be massively problematical.

Air-dried or seasoned oak

Air-dried oak is the preferred choice for a glazed frame structure such as an orangery, conservatory or garden room. This grade of oak is typically air dried for between seven and eight years before being machined. This gives a much more stable product, as oak dries at approximately 20mm per year.

Long-term air drying makes the timber not only more expensive but also harder and more difficult to machine.

Whilst the outcome will potentially increase the overall cost (in terms of materials and production), this uplift can be seen as a sensible investment to avoid some of the pitfalls that come from the widespread use of green oak by many oak frame suppliers.

Which should I choose?

It completely depends on the application. Green oak is entirely appropriate for an oak outbuilding, carport or garage, which is unlikely to contain many windows.

If, however, the design brief is to construct an orangery kitchen extension, for example, which will become the heart of the home (and used all year round), then the quality of materials and finish is essential to the end result.

When researching potential oak frame suppliers, it is important to ask manufacturers about the grade of oak they will use and, ideally, ask to see examples of their completed oak to see how it has performed and weathered over time.

Do your research

An oak-framed orangery or garden room is clearly a significant investment, so it’s important to start with a material that can withstand time and changing seasons.

Whilst oak is a wonderfully durable timber, not all oak is the same. As a natural material, clearly, no two pieces of wood are ever the same, but what is important to note is that the selection of the type of oak used for manufacturing is critical and can alter from one supplier to another.

Homeowners considering an oak-framed extension should conduct their research carefully, balancing the twin parameters of quality against cost.

Further information....

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