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DIN 4074-5 is being amended: Small tunnels made by wood-boring insects in hardwood intended for load-bearing components will henceforth be permitted up to a diameter of 2 mm. This will allow oak timber with such traces to be classified according to its load-bearing capacity in the future, provided it also meets all other requirements of the respective strength class.
The change therefore affects wood that, until now, could not be graded according to DIN 4074-5 solely due to small insect tunnels. This new regulation opens up additional opportunities for the use of oak in timber construction.
What changes with the new DIN 4074-5?
DIN 4074-5 governs the grading of sawn hardwood based on load-bearing capacity. The previous 2008 version did not permit insect damage in grading classes LS 7, LS 10, and LS 13. Consequently, even small boreholes meant that the affected timber could not be classified according to this standard.
The new version adjusts this criterion. Tunnels and boreholes from fresh-wood insects will be permitted up to a diameter of 2 mm in grading classes LS 7, LS 10, and LS 13. Larger tunnels remain excluded.
This change does not mean that every piece of wood with small traces of insect damage is automatically suitable for load-bearing purposes. Knots, cracks, grain slope, curvature, and all other grading characteristics must still be fully assessed. What is new is that small tunnels no longer fundamentally prevent grading based on load-bearing capacity.
Why is the assessment of insect tunnels being adjusted?
The oak pinhole borer occurs primarily in weakened oak trees and freshly felled wood. Drought periods and high temperatures are increasingly stressing oak stands, thereby facilitating infestation. Consequently, the typical black tunnels are found more frequently in sawn timber.
Under the previous DIN 4074-5, a single such trace was enough to exclude the timber from being graded for load-bearing capacity. Yet, a small tunnel alone does not indicate whether the entire piece of wood possesses the required load-bearing capacity. The upcoming change therefore allows for a more precise assessment: the deciding factor is no longer just whether tunnels are present, but also how large they are.
What does the change mean for oak wood?
Oak with small insect tunnels can still be strong and suitable for load-bearing applications despite this feature. Under the previous regulation, it could not be assigned to a DIN 4074-5 grading class. This meant it was excluded for such applications, even though its other characteristics might have met the requirements.
With the new regulation, such wood can be regularly inspected and graded in the future. If a piece of wood meets all the requirements of the intended grading class and the tunnels do not exceed the specified diameter, this individual feature will no longer prevent it from being classified.
The change to the standard does not mean a blanket expansion of permitted wood characteristics. Rather, it removes an exclusion criterion that previously treated small and large tunnels alike.
The black tunnels originate in fresh wood
The oak pinhole borer belongs to the category of "fresh-wood insects." It attacks weakened oaks as well as freshly felled or sufficiently moist wood. A fungus introduced by the beetle grows in the tunnels it creates, serving as its food source.
In dry wood, this fungus can no longer develop. The oak pinhole borer is thus deprived of the conditions it needs to survive. The black tunnels remain visible in the wood, but do not imply an ongoing infestation in technically dried timber.
Load-bearing capacity and visual grading remain separate issues
DIN 4074-5 evaluates sawn hardwood exclusively on the basis of its load-bearing capacity. The new admissibility of small tunnels therefore says nothing about the visual appearance of the wood.
In grading specifications, insect tunnels can still be a deciding factor. If a grade without visible boreholes has been agreed upon, wood with such features does not comply with this agreement, even if it can be assigned to a load-bearing grade according to the new DIN 4074-5.
The change therefore does not affect every form of wood grading, but exclusively the technical classification of sawn hardwood for load-bearing components.
When does the new regulation apply?
DIN 4074-5:2026-05 has already been published but is currently being corrected. Purchasers of documents already delivered will receive the correction automatically.
Until the correction is available, the specific requirements and the timing of their application must be checked against the current version of the standard. Information on this is provided by DIN Media.
An important step for oak in timber construction
The upcoming amendment to DIN 4074-5 enables a more nuanced assessment of oak wood with small insect tunnels. Instead of excluding every affected piece of wood based solely on this characteristic, its actual suitability can in future be evaluated as part of a comprehensive load-bearing assessment.
This allows more oak timber to be put to appropriate use without lowering the requirements for the respective grading class. Small traces of fresh-wood insects remain visible – but no longer fundamentally prevent technical classification.
If you have any questions about available wood species, dimensions, and grades, please feel free to contact us.
