Long-term durability of fire protection OF WOOD requires knowledge and regular maintenance

The fire protection of wooden facades must remain at the required level throughout the lifecycle of a building – at least 30–40 years. However, the actual performance of fire protection is not always properly verified and monitored. Nordtreat ensures the performance of its flame retardants by meeting the requirements of standards such as EN 16755 together with solution-specific maintenance programs.

In Europe, the long-term durability of fire protection in wood structures is typically verified by classifying products according to harmonized standard EN 16755 (Durability of Reaction to Fire Performance). However, the test results are not always sufficient to ensure real fire protection throughout the building's life. Responsible builders and building control authorities must understand the details of the fire protection treatment that has passed the test. 

There is simply no such thing as maintenance-free fire protection for wooden facades

Nordtreat's Vice President of Technology Mikko Tuominen says there are many misconceptions and, therefore, risks associated with the long-term durability of wood fire protection. The largest misconception is whether the fire protection of wood facades, once applied, will last the expected technical life of the facade or even the whole building. Additionally, the requirement and type of maintenance play a significant role in the equation.

"Regardless of the fire protection technology used, years of weathering will always affect both the performance of the fire protection and the appearance of the building. Therefore, promising complete freedom from maintenance is irresponsible."

Mikko Tuominen, Vice President, Technology of Nordtreat

"The requirements of standard EN 16755 must be met, but when it comes to testing based on accelerated weather exposure, it cannot fully reflect the actual performance of the fire protection in varying weather conditions over the years. Unfortunately, the actual performance of fire protection is far from always guaranteed," Mikko Tuominen continues.

Weather exposure will inevitably affect the appearance of a wooden facade over time. There is a risk that a wood cladding that has been fire-protected in the past will be painted with a product for appearance reasons, which will weaken the fire protection and at the same time increase the fire load of the wood structure.

Nordtreat's fire protection technology and maintenance programs ensure long-term durability

Nordtreat's bio-based NORFLAM fire protection technology allows the translucent flame retardants to be absorbed and fixed into the wood material. 

Nordtreat's NT DECO and other NORFLAM flame retardants for wood cladding have passed the EN 16755 standard tests and have been classified for exterior use in DRF class EXT. The respected French Technology Institute FCBA was one of the laboratories responsible for the classification tests.

Nordtreat performs continuous research and testing on the durability of flame retardant treatments and coatings. A Nordtreat research engineer handles an accelerated weathering apparatus in Nordtreat's research center in Vantaa, Finland.

Nordtreat's flame retardants also have clearly defined maintenance programmes. Maintenance treatments are carried out every 5–10 years, depending on the product and level of weather exposure. This ensures that the fire protection of the wood facade is maintained at the required level throughout the building's lifecycle.

Many fire protection technologies have long-term durability challenges 

Fire protection technologies used for wood include heat-swelling flame retardants and fire protection technologies based on impregnation chemistry. 

The challenge of heat-swelling flame retardants from a long-term durability perspective is that the product may need to be repainted immediately upon installation, or at the latest at the first maintenance treatment. Painting over the fire protection almost always increases the fire load, so the results of a passed EN 16755 test are no longer valid. In addition, the effectiveness of the flame retardant treatment is reduced over the years by the effects of sun and rain.

"The standard test should be subjected to the surface treatment that the building will actually receive. When the surface of the flame retardant paint starts to look worn over time, subsequent maintenance coatings often only further degrade the performance of the flame retardant."

Mikko Tuominen, Vice President, Technology of Nordtreat

Fire protection of wood based on impregnation chemistry may be a more durable solution than swelling flame retardant paints, but its performance will not last the lifetime of the building. 

"Over time, the surface concentration of the fire-protecting chemical in the wood decreases and the façade starts to look worn. The surface fire class of the impregnated façade no longer meets the fire safety requirements", Mikko Tuominen says.

Natural and accelerated weathering methods assess service intervals for flame-retardant materials.

Note on testing and compliance with the maintenance programme

The most important thing is to know what has been tested and how. Tests according to EN 16755 should be carried out both before and after the weather load. In addition, the product being tested should not be repainted during or shortly after installation. As Nordtreat flame retardants do not require a separate surface treatment, this problem does not exist.

"Our maintenance program guides you in choosing the right maintenance interval depending on the product to be used and the conditions under which the building product will be installed. As a rule, the maintenance treatment is always carried out with the same flame retardant as the original treatment."

Mikko Tuominen, Vice President, Technology of Nordtreat

The EN 16755 standard is being developed to improve the safety of fire protection

As long-term durability of fire protection is an essential issue for the safety of wood construction, Nordtreat is involved in the development of standards in this field and actively participates in the work of CEN (European Committee for Standardization) working groups.

"The requirements of the EU standard on fire protection of facades need to be reassessed. We are involved in the evaluation working group and will propose improvements during 2025", says Mikko Tuominen.