Traditional oak framing has been a popular building system for centuries because of the many benefits associated with using green oak. The most prominent benefit is that green oak is often freshly cut, and still contains a high level of moisture. This makes it easier to work with and shape into the desired frame.
Here are more surprising benefits of using green oak for traditional framing work:
- Demonstrated durability and strength: Traditional oak framing using green oak has a proven track record of durability and strength. There are many examples of oak-framed buildings that have lasted for centuries, withstanding harsh weather conditions and natural disasters like earthquakes.
- A proven building system: The use of green oak in traditional framing is an age-old building system. The frame is designed to withstand the natural shrinking and settling that occurs as the wood dries out, making it an ideal choice for a long-lasting, sturdy construction.
- Tighter joints: Green oak frames are constructed with joints designed to tighten and become stronger over time as the wood dries out. This natural process ensures a tight and secure frame that is less prone to movement over time.
- Eco-friendly: Green oak is an eco-friendly choice, utilising a renewable resource that requires minimal processing.
Green Oak vs. Kiln and Air-Dried Oak
Air-dried or kiln-dried oak may be easier to work with initially, but neither of these offers the same benefits as green oak. Drying oak in a kiln speeds up the drying process and can result in a weaker and less durable frame. Air-dried oak, on the other hand, may take longer to dry but can still lack the benefits of green oak in terms of tight joints and proven durability.
So, traditional oak framing using green oak is a proven building system that offers durability, strength, and tighter joints. Its long history of demonstrated durability makes it an eminently reliable choice for a sustainable and long-lasting building.
Drying oak beams of structural size involves removing moisture from the wood to reduce its weight. This, in turn, prevents warping or cracking and increases overall strength. The correct length of time for drying oak beams depends on the cross-section size, initial moisture content, and drying conditions.
In general, air drying is the most common method for drying oak beams. The beams are stacked with spacers between them to allow air circulation and are left in a dry, well-ventilated area where they will be protected from direct sunlight and rain.
To give an example of this, oak beams with a cross-section size of 8×8 inches can take about 1 year per inch of thickness to air-dry properly. So, a 10-inch thick beam would take about 10 years to dry completely. However, if the initial moisture content is high, the drying time may increase.
Here are a few examples of different oak beam cross-sections and their estimated air-drying times in the right conditions:
- 6×6 inches: about 6-8 months per inch of thickness
- 10×10 inches: about 1-2 years per inch of thickness
- 12×12 inches: about 2-3 years per inch of thickness
It is important to note that these are only rough guidelines, and the actual drying time may vary depending on the specific conditions and characteristics of the wood. To ensure that the oak beams are properly dried, use a moisture meter to monitor the moisture content and adjust the drying time accordingly.
It is also important to note that not every oak frame manufacturer will be air drying their oak correctly, or for the right length of time. Some may not be allowing sufficient time for the timber to dry fully, or may even be using substandard timber that has not been properly prepared for air drying.
Oak Timber Grades
When considering purchasing an oak frame building, it’s important to understand the different grades of oak available. Structural engineers specify the oak grade based on factors like wind loadings, orientation, and elevation, to ensure that the oak frame meets the necessary strength requirements.
At English Heritage Buildings, our oak frames are made using a higher grade than the general industry standard, and we have fully-qualified timber graders who ensure that the oak we use meets the structural engineer’s specifications.
There are different grades of oak available, such as QPA and QP1. These grades belong to the appearance class EN957-1, which is used by structural engineers to specify the strength class of the oak. These strength classes are further defined in EN 338.
When ordering from Europe, QP1 constitutes sawn timber with:
- Practically sharp arrises
- Fully or partially intergrown sound knots, permitted if the diameter is less than half the face width
- Two dead knots, permitted per linear metre if less than one-quarter face width
QPA is sawn timber with:
- Sharp arrises
- Sound sapwood, permitted on two arrises if the total width is less than 15% of the face width
- Fully or partially intergrown sound knots, permitted if the diameter is less than one-third of the face width
- Dead knots, permitted where equivalent to two dead knots with a diameter less than 15mm per linear metre
English Heritage Buildings’ Requirements
We follow strict oak quality requirements when purchasing fresh green oak beams, including:
- Sawn timber with sharp edges
- Tolerance of small quantities of sound sapwood on two edges maximum
- Sound knots are accepted if the diameter is below 50% of the total width
- Grain angle not exceeding 1 in 4
Our regulated packing requirements include identifying packs by customer name and order number, and allocating an identifying colour to each supplier, which needs to be placed at the end of each beam.
In essence, we pride ourselves on employing a superior grade of oak that surpasses the prevailing industry standard. Our team of highly skilled timber graders only select oak that precisely adheres to the specifications set by structural engineers. It is crucial to comprehend the wide array of oak grades accessible and the various factors that dictate the imperative choice of grade required for your unique construction project.