Articles: Structural Oak Beams

Are Oak beams structural?

Fresh Sawn Oak and Air-dried Oak are indeed structural, infact, the construction industry has been utilizing oak for centuries to erect all manner of structures. As I write this article, thousands of structural oak beams are being used in France to restore the Notre Dame to its former glory and if that doesn’t represent oak’s structural strength I’m not sure what will.

Striking a perfect balance between cost and strength, European Oak is widely used from vast supporting superstructures to solid oak garden gazebos and in terms of strength to weight ratio its actually tougher than steel.

Structural Green Oak beams

Fresh Sawn Green Oak refers to beams cut fresh from the log, you can buy structural oak beams online. Green Oak is ideal for structural use because of its impressive strength and excellent durability, while its green and fresh sawn it is also much easier to work with and cut through.

Overtime the Oak will air dry and start to undergo shrinkage which is the process that produces the typical characteristics of aged oak such as splits, cracks and surface checking. Not to worry though this doesn’t affect the structural integrity and will actually bolster the oak and make it harder and more difficult to mark/damage.

Structural Grade Oak Beams

Our Fresh Sawn Green oak is available in two grades, QPA and QP1 which is the European visual grade assigned to the oak before its imported into the UK.

QPA is the top grade of European Oak and is structurally equivalent to the UK strength class D30. QP1 is the standard structural grade of European Oak and equates to UK strength class D24.

We supply bespoke oak structures in kit form that have all the carpentry and joinery complete ready for you to assemble. We produce these structures out of a combination of our QP1 and QPA graded European oak.

If you’re interested an buying an oak structure, head over to our Gazebo and Pergola 3D designer pages.

What strength grade is Oak?

Oak can be strength graded from D18 up to D40 using the BS EN 338 classification system. More information in a previous article here .

For a brief overview, European Oak beams imported from the continent are visually graded to a maximum of QPA which is officially documented to equate to D30 grade.

QP1 is the second best grade assigned to European Oak imported from the continent and is often used when a project specifies 'standard structural grade' or similar. Whilst QP1 Oak performs twice as well as softwoods the price doesn't reflect it and as you'll see from many different suppliers at the moment the drop in features such as durability is far more than the cost saving.

The highest grade Oak can achieve is D40 grade, to achieve D40 grade, it must be assigned a TH code. Specifically, THA.

TH codes are assigned by the UK grading system, there are four codes. THA and THB are both classifications of Large Section Oak intended for use in a service class 3 environment. TH1 and TH2 are for smaller section oak and dried oak for use in class 1 and 2 environments.

Service class environments is, put simply, where the oak will be used. To assign THA grade classification (D40 strength grade) the Oak must:

  • Exceed a cross sectional area (width x thickness) of 20,000mm2
  • Have sections no less than 100mm
  • Meet service class 3 (installed at a high moisture content with climate expected to remain wet, such as outdoor Gazebo’s and Pergola’s)

Generally speaking, the biggest impact on structural strength is determined by easily identifiable features such as knot size and proximity, and the size of splits/fissures across the face of the beam. The higher the grade, the more strict the conditions surrounding these features.

We only supply our beams to a maximum of QPA appearance grade which regardless of section, will always be equivalent to D30 grade. For D40 Oak the highest available visual grade of whichever grading technique is used must be achieved in addition to the section criteria as mentioned above.

iWood’s Structural grade Green and Air Dried Oak beams

At iWood we pride ourselves on transparency and upfront pricing. As such our European oak is graded on the continent prior to import by certified European Graders. Ensuring you can be certain that you are getting the correct grade of oak straight from the source.

We also offer structural oak beams air-dried. Air-dried oak is initially felled and graded to QP1 visual grade (D24), it is then stored and air-dried for between 1 and 5 years.

Air dried Oak is quintessential to any traditional aesthetic and is a very popular option for structural oak indoors due to its lower moisture content and rustic appearance.

You can expect air-dried oak to exhibit all the natural changes of weathered and aged oak such as splits, cracks, surface checking and even UV bleaching. It’s due to the physical changes through the air-drying process that the beams are not strength graded when supplied.

Its important to note that air dried oak cut from non standard section sizes may have both weathered faces and fresh sawn faces unless Planed All Round.

Oak is in our DNA and over the years we've developed strong relationships with numerous sawmills on the continent allowing us to consistently and reliably supply high quality European Oak at competitive prices. When it comes to Oak you’re in good hands with iWood.

iWood has supplied some impressive structural beams and with Oak you can get some rather staggering sections, from 10m lengths in a single piece to 400mm sections. If structural timber is required, oak is quite often the best species for the job. If you cant price up your requirements on our European Oak page, please send in your enquiry to or give us a call and we’ll produce a quote for you.