What Grade Oak Are You Buying for Your Oak-Framed Building?

When specifying oak-framed buildings, it’s common to hear suppliers say they all use the same oak. In one sense, that’s true. Most structural oak frames in the UK are produced from Quercus robur, a species widely recognised for its durability and strength. However, the real question you should be asking is not what type of oak is being used, but what grade of oak it is.

If you’re working with oak-framed garages, garden rooms, or other structures, understanding timber grading is essential. The structural engineer will determine the strength class required for the frame based on the specific project conditions. These calculations take into account important factors such as the building’s location, elevation, orientation, and expected wind loadings.

Ensuring that the oak supplied meets this specification is critical for structural performance, long-term durability, and accurate installation.

IMG 9520

Oak Grades and Structural Strength Classes

When working with structural oak, there are two classifications you will often encounter: appearance classes and strength classes. Appearance classes describe the visual quality of the timber, while strength classes relate directly to the structural performance required by the engineer.

Two common appearance classes used within structural oak framing are QPA and QP1. Both are appearance classes EN957-1. These then relate to Strength Classes EN 338, which the structural engineer uses to specify the strength class the oak needs to be.

QPA

QPA is generally associated with the D30 strength class, which is widely used as a standard structural grade for oak frames. This grade provides the strength required for most structural applications without requiring oversized timber sections.

QP1

QP1, by comparison, relates to the D24 strength class. While still suitable in certain circumstances, this grade typically requires larger timber sections to meet the same engineering calculations. For projects involving oak-framed structures such as garages, carports, or garden rooms, this can influence both the design and material requirements.

For professionals specifying bespoke structures, understanding this distinction helps ensure the timber supplied aligns with the structural design.

Ordering Oak Timber from Europe

When ordering from Europe, you will find that they classify their grades as follows: 

QP1 

  • This is sawn timber with particularly sharp arrises and a permitting wane of less than 10% of the face, and width across no more than 30% of the length. 
  • This width tolerance is increased to 15% for sections above 250 x 250mm. 
  • Sound sapwood is permitted on two arrises if the total width is less than 15% of the face width.
  • Fully or partially intergrown sound knots are permitted if the diameter is less than half the face width. 
  • Two dead knots are permitted per linear metre if the diameter is less than one-quarter face width. 
  • Boxed heart is permitted, as well as traces of heartwood on both faces. 
  • A slope of grain less than 12% is permitted and should not exceed 20% locally. 
  • Brown streak, black holes, and brown pith are all permitted on a certain number of pieces. 
  • Unsound knots, frost crack, ring shake, star shake, curly grain, bark pocket, unsound sapwood, rot, and white holes are all excluded. 

QPA 

  • This is sawn timber with sharp arrises; in case of pieces longer than 3m, a wane less than 10% of the face width is permitted across no more than 25% of the length. 
  • Sound sapwood is permitted on two arrises if the total width is less than 15% of the face width. 
  • Fully or partially intergrown sound knots are permitted if the diameter is less than one-third of the face width. 
  • Dead knots are permitted where equivalent to two dead knots with a diameter less than 15mm per linear metre. 
  • Boxed heart is permitted, as well as slight traces of heartwood, on two faces. 
  • A slope of grain less than 7% is permitted and should not exceed 12% locally. 
  • Unsound knots, end shake, frost crack, ring shake, star shake, curly grain, bark pocket, unsound sapwood, brown pith, brown streak, rot, and holes are all excluded.

Why Timber Grading Matters

Structural oak is a natural material, and each beam will contain its own characteristics. This is why professional timber grading is essential. Qualified graders assess each beam to ensure it meets the required structural standards and that it doesn’t contain defects that could compromise performance.

Examples of defects that make timber unsuitable for structural use include:

  • Woodworm or insect damage
  • Bug holes
  • Ring shake or heart shake
  • Rot or internal decay
  • Soft or unsound knots
  • Bark inclusions or black veins

Using improperly graded timber introduces unnecessary risk. A structural defect within a beam can lead to weakness within the frame, which is why professional grading plays such an important role in the manufacture of oak-framed buildings.

This approach provides reassurance that the oak timber used in our frames is suitable for structural use and aligns with the engineer’s specification.

The Oak Frames Direct Grading Process

At Oak Frames Direct, quality control begins long before the timber reaches the workshop. Across Europe, there are roughly 55 to 60 oak mills capable of producing structural oak beams at a commercial scale. However, only a small number consistently produce the quality required for structural frame manufacturing. Through experience and ongoing assessment, we work with that select group of mills capable of maintaining the standards required for structural oak framing.

Even with carefully selected suppliers, timber still undergoes multiple stages of inspection and grading. This is performed by our in-house graders. These timber graders are fully qualified, trained, tested, and recertified annually by BM TRADA, helping to ensure that all structural timber meets the required standards. During the grading process, beams that do not meet our quality standards are rejected. In many cases, this can result in rejection rates of up to 35–40% of incoming timber.

This approach provides reassurance that the oak timber used in our frames is suitable for structural use and aligns with the engineer’s specification.

Packing Requirements

1. Packs will need to be identified by customer name and order number. The size needs to be identified at one end of each beam.

2. An identifying colour will be allocated to each supplier, which needs to be placed at the end of each beam. A clear and concise packing list/delivery note.

3. The maximum weight of an oak bundle is 3000kg.

4. Timbers must be stacked separating each layer with sticks every 750mm to prevent bowing.

5. Stacks must be in descending order.

6. Banding straps must be used every 1.5m.

7. If metal straps are used, a protector must be used to prevent timber staining.

8. When ordering “stock”, the same-sized beams need to pack together. Customer order requirements (random lengths) need to be kept together.

Oak Frame Full Height Porch

Why This Matters for You

If you’re installing an oak-framed building or structure, the reliability of the timber specification is critical.

Correct grading ensures that:

  • The structural calculations are accurate
  • The timber sections meet the engineer’s requirements
  • The frame performs reliably over time
  • You can confidently explain the material specification to your client

It also removes uncertainty during installation. Knowing the timber has already been carefully graded and verified allows you to focus on the build itself rather than worrying about the suitability of the materials supplied.

A Reliable Standard for Oak-Framed Structures

While many suppliers may say they use the same oak, the difference lies in how that oak is sourced, graded, and verified before it becomes part of a structural frame. In our work, every frame is manufactured to BM TRADA Q-Mark equivalent standards, using precision machining and a tightly controlled grading process to ensure structural consistency.

Whether you’re specifying oak-framed structures, designing oak-framed buildings, or supplying a bespoke oak frame kit, the grading of the timber is one of the most important factors in ensuring the finished structure performs exactly as expected.

Speak to the Team or Configure Your Frame Online

If you’re specifying oak-framed garages, garden rooms, porches, or even a series of oak-framed structures, our team is here to help. Use our Online Builder to configure your frame and receive a clear, reliable quote, or contact our team directly to discuss the requirements for your next project.