Renowned researchers Birgit Östman and Lazaros Tsantaridis wrote in 2016: “It’s relatively easy to obtain improved fire performance of wood products.” Anyone can treat wood with fire retardant. The real challenge is maintaining the effect outdoors, in all weather conditions. A growing body of research shows that this is virtually impossible without periodic maintenance. On this topic, too, science is pitted against industry. Time to let science speak...

The scientific consternation:

The sustainability of fire-retardant treatments has been a scientific concern for many years.
Just as with ecological issues like microplastics, this is a highly technical and barely visible problem, and is therefore often ignored by the industry.

Here, the interests of the industry are often diametrically opposed to those of science: while scientists warn of rapid degradation, the market continues to sell based on laboratory tests, unusual white papers, impossible claims, and so on.
In fact, the industry sells itself as a knowledge provider, which only exacerbates the problem.

If we want to successfully continue the ecological revolution in construction, we urgently need to break this pattern.
We cannot wait for standards to retrospectively reveal major problems and for lawsuits to ensue.
We must act now.

What the science says:

Engström & Psajd (Lund University, 2024)

Engström and Psajd investigated the durability and effectiveness of fire retardant treatments in accelerated and natural aging.
They did this through literature studies, interviews, and practical tests.

The scientific research showed that natural aging already has a significant effect on the ignition time and the Total Heat Release Rate (THRR) after just a few weeks.
Using infrared spectroscopy, they demonstrated that the concentration of fire retardant substances decreased noticeably after just a few weeks.
The research shows that the material's properties changed after just a few weeks.

Carolina Arvidsson (Lund University, 2025)

The most recent step came from Carolina Arvidsson, supervised by Konrad Wilkens F. Brown (postdoctoral fellow), at the Department of Fire Safety Engineering, Lund University.

Ms. Arvidsson wrote her impressive thesis based on realistic tests. She conducted a field study in which facade components were dismantled and tested after one to two years of exposure in southern Sweden.

The samples came from the north and east facades, orientations that normally offer the best chance of success due to lower UV exposure.
However, here too, the fire reaction was significantly degraded.

Arvidsson concludes clearly:

- There is a lack of clear documentation and understanding of fire-retardant products.
- There are no conclusive maintenance instructions to guarantee a lasting fire reaction class.
- There is a significant difference between a successful fire test and actual performance on a building scale.
- Artificial aging produces very different results than natural aging.

In fact, Carolina discovered that there is a possible correlation between the color of the wood and the condition of the facade.
The color of the wood could hypothetically serve as a first indicator for estimating the quality of the fire retardant.
If the wood turns gray, its fire-retardant properties will significantly degrade.
A particularly interesting hypothesis worthy of further investigation.

Here you will find the link to this scientific document: CLICK HERE.

Time as a missing factor:

The core is clear:
A fire test is a snapshot, and time, or aging, must be systematically incorporated into the fire safety analysis.

A facade can easily meet fire class B upon completion, but within a few months, it can drop to class D or lower.
This transforms a fire-retardant facade from a protective shell into a potential fire spreader.

Periodic post-treatment is therefore unavoidable and must be carefully considered and demonstrably correct.
A superficial coat of paint or added resin is merely a temporary extension and is insufficient.

Situation in Europe:

EN 16755 has been in place since October 2017, and it allows for various methods of assessing durability in Europe. Although there are several options, the natural aging test (EN 927-3) with an SBI test (EN13823) is the only definitive method in the event of a dispute.

Only this test method provides legal certainty in the event of problems.

Almost eight years have passed, and yet not a single fire-retardant treatment has successfully completed this test.
This means that the market today relies heavily on test methods that science has clearly shown to be flawed for years.

Yet, we see that:

- Some suppliers cannot demonstrate anything at all.
- Others rely on invalid standards.
- Many refer to the combination of accelerated aging (EN 927-6) and Cone Calorimeter (ISO 5660-1), which science frequently deems unrepresentative.

Meanwhile, the first practical problems are becoming apparent:

A scientist familiar with wood and fire reaction classes will immediately recognize the (very) problematic buildings that have been or are being built. Facades that no longer meet requirements due to rapid degradation of fire-retardant treatments.

The first project in Flanders requiring the dismantling of a facade, with all the attendant financial consequences, has now been completed.
Fire reaction class B was demonstrated via the SBI test (EN13823), but quickly plummeted...

Composites are not an alternative:

(Ecological) composites are increasingly being promoted as the solution.
Fortunately, the answer isn't so simple.

Due to the presence of thermosets, they are almost always a source of microplastics and will never match wood.
At the same time, many composites now also use fire-retardant treatments, and here too, the time effect is ignored.

It's comparable to applying a coating to a car tire and then claiming the tire will never wear out.
In practice, everyone knows that coating disappears as soon as the tire is used.
The same happens with fire retardants in or on composite materials.

A call to the construction sector

Science is unanimous:

- Fire-retardant treatments degrade outdoors.
- Only natural weathering is representative.
- Periodic maintenance is necessary.

Will this have a negative impact on the cost of facade cladding?
Probably, but this will level the playing field and prevent an avalanche of problems in the future.

Therefore, an appeal to architects, contractors, and clients:

- Always request independent test results after natural weathering.
If these are lacking: have them performed. This is your right.

- Ensure that the durability can be demonstrated with a notifying body.
Are you adding a fire-retardant treatment to the facade?
Have an independent third party confirm that the tested products are representative and that the exposure period has been correctly recorded.

- Always check whether the claimed standard is applicable to your project.
Incorrect standards are often used when determining the durability of (modified) wood. This also frequently occurs with fire reaction classes.

Ask for clear maintenance instructions. Carolina Arvidsson's research (Lund University, 2023) emphasizes this once again.

In short: ask the right questions and demand substantiated answers.

We can't wait for a new fire inferno to confront us with the facts.
The ecological revolution in construction is accelerating, and wood will be an absolute leader.
As we approach technical perfection, this revolution will only accelerate further.