Nearly two and a half years ago, I warned of an earthquake in the timber industry. The European standard EN 16755 was expected to undergo substantial revisions, potentially with far-reaching consequences for manufacturers of fire-retardant-treated wood. Remarkably, there was little substantive response from the commercial sector. In fact, I noticed that some suppliers were making increasingly bold commercial claims about the long-term retention of reaction-to-fire performance. On 18 October 2026, the revised EN 16755 was officially ratified. The changes I predicted have now become reality. But what exactly is happening?

On 10 June 2024, I published the blog "Yet another earthquake in the wood world - Possible adjudstment of EN 16755" (Click here to read).

Shortly after modified wood was removed from the well-known CWFT (Classified Without Further Testing) provisions, the durability of fire-retardant treatments came under scrutiny.

In that earlier blog, I explained how EN 16755, the European standard for the retained reaction-to-fire performance of fire-retardant-treated wood, was likely to change.

What exactly is changing?
EN 16755 is the European standard used to assess the retention of reaction-to-fire performance in fire-retardant-treated wood products.

The standard distinguishes between three application classes: INT1, INT2 and EXT.
EXT is particularly relevant for timber cladding directly exposed to weather conditions.

The revised edition introduces several important changes:

- The Cone Calorimeter (ISO 5660-1) is removed as an assessment method.
- The SBI test (EN 13823) becomes the designated method for assessing reaction-to-fire performance after weathering.
- At least two SBI tests must be carried out after weathering.
- The previous links between classification and the service life of the wood product are removed.
I find that last point particularly interesting.

What does EN 16755 say about service life?
The previous edition, published in 2017, still established a connection, to some extent, between certain classifications and the service life of the wood product.

In 2026, this connection is deliberately abandoned.
The revised standard explicitly states: "Classification does not consider service life."

In other words, the classification does not take service life into account.
Furthermore, the standard clarifies that a classification does not indicate how long the reaction-to-fire performance will be maintained.
Feel free to read that last sentence again.

A manufacturer can therefore demonstrate that a product still meets certain reaction-to-fire performance requirements after a prescribed weathering procedure.
However, this does not demonstrate that these performances will be maintained over a claimed service life of several years.

These are two fundamentally different statements.

What about maintenance or retreatment?
This is where things become particularly interesting.

EN 16755 requires manufacturers of products intended for exterior applications (EXT) to provide maintenance instructions to preserve their performance. However, the standard does not establish how many years these performances will be maintained.

An EXT classification therefore does not automatically mean that a fire-retardant treatment will remain effective throughout the entire service life of a building without maintenance or retreatment.
Of course, this does not mean that every treatment necessarily requires periodic reapplication.

But anyone claiming that a treatment will not require retreatment for 30 or 50 years must be able to substantiate that claim independently.
An EXT classification is not a service-life guarantee, nor is it proof that retreatment will be unnecessary throughout the entire service life of a building.

So what exactly are such commercial claims based on?
I think that is a particularly interesting question.

What does this mean for existing projects?
The approval of EN 16755:2026 obviously does not mean that all existing timber façades have suddenly become unsafe or must be replaced.
Furthermore, the standard is not a directly applicable European law.

Meanwhile, I have noticed a significant increase in attention being paid to the fire safety of existing timber cladding.
Fire safety consultants are raising new questions, technical documentation is being reassessed, and several projects have already been identified where timber cladding has been rejected and is currently being replaced...

The issue is more prominent than ever and is being actively investigated.
What performance was originally demonstrated?
Which construction configuration was actually installed?
And what performance can reasonably be expected today?

These questions are becoming increasingly important.

And what about untreated wood?
Forestlines® achieves reaction-to-fire classification B-s1,d0 without any fire-retardant treatment.
EN 16755 therefore does not directly apply to our system.

Nevertheless, we have been investigating the influence of natural weathering on the reaction-to-fire performance of untreated wood for quite some time, and this research is beginning to produce particularly interesting results.

The most critical Forestlines® configuration (taking into account factors such as wood species, board width and construction build-up) has now undergone two SBI tests according to EN 13823 following natural weathering in accordance with EN 927-3.
Across these two SBI tests, the average values of the relevant assessment parameters remained within the limits applicable to reaction-to-fire classification B-s1,d0.

We have also investigated material recovered from existing façades that have been exposed to weather conditions for many years.
By comparing these results with our controlled weathering tests, we can develop a better understanding of how reaction-to-fire performance evolves over time.

What does the future hold?
Our research into the weathering of untreated wood will be significantly expanded in the coming period.
We are currently preparing an extensive scientific research programme to investigate the influence of natural weathering on the reaction-to-fire performance of wood as a base material in much greater detail.
The objective is not simply to investigate Forestlines®, but to develop fundamental knowledge that could benefit the entire timber industry.

We want to gain a better understanding of the relationships between wood species, material properties, exposure duration and reaction-to-fire performance, and to publish our scientific findings.

We do not want to be in a position where we are marking our own homework. That is why we have chosen to conduct our fire tests at PEUTZ and Warrington Fire Ghent, both independent fire testing laboratories.
Peutz also carries out the natural weathering exposure according to EN 927-3.
This ensures that our research is conducted and assessed with the involvement of an independent party.
Rather than conducting our own fire tests and subsequently approving our own results, we rely on independently performed testing, with results that must be verifiable and reproducible.

The earthquake is a reality
Almost two and a half years ago, I warned about this revision of the standard. The European revision has now been approved.

However, I want to make one distinction absolutely clear:
This earthquake is primarily taking place in the world of fire-retardant treatments, not in wood as a base material.
Wood naturally has certain reaction-to-fire properties, which can change as a result of weathering.

We are also investigating these changes extensively.
A fire-retardant treatment can improve these properties and enable treated wood to achieve a higher reaction-to-fire classification.
But what happens to that improvement, which may or may not be temporary?
How much of the original effectiveness remains after prolonged exposure to weather conditions?
Does the treatment gradually lose its effectiveness, and if so, how quickly?
And most importantly, what are the consequences for the reaction-to-fire performance of the complete façade assembly?

Partial leaching of a treatment does not automatically mean that the product will fall into a different reaction-to-fire class.
But neither should we simply assume that the original classification will be maintained.
Only when we understand how reaction-to-fire performance evolves over time can we properly assess the consequences for fire safety based on sound evidence.

Demonstrating a reaction-to-fire classification is one thing.
Demonstrating that this classification is maintained after a prescribed weathering procedure is another.
Demonstrating that these performances will be maintained throughout the entire service life of a building is something else entirely.

This critical approach applies to fire-retardant-treated wood, but naturally also to our own products.

And that brings me back to a phrase I used almost two and a half years ago: "Prove it to me."
That is exactly what we are trying to achieve through our research.

Knowledge is essential for innovation.