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Innovation blog open timber cladding reaction-to-fire class B

19/06/2026
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For the first time, vertical timber cladding with an open joint is possible in reaction-to-fire class B – a groundbreaking development that the timber construction sector has long been waiting for.

Since the change to the regulations on the reaction-to-fire class of timber cladding last summer, we already hold reaction-to-fire classification reports for our fire-retardant closed cladding with traditional fixing.

What is new is that there are now also certified solutions for open-joint cladding with traditional fixing, nailed or screwed, with a maximum gap of 8 mm. This both aesthetic and fire-retardant façade solution is now a reality thanks to a smart combination of fire-retardant treatment with polymers, considered design and careful installation. As a result, you can now apply open timber cladding vertically that meets the strict requirements of reaction-to-fire class B.

Please note: the certification does not yet apply to timber profiles with a colour finish. This is, however, actively being worked on.

Technical requirements for reaction-to-fire class B

  • Wood varieties: thermo ash, thermo Clear Pine, thermo pine
  • Boards with a minimum thickness of 19.5 mm and a width ≥ 72 mm
  • Vertical installation with a gap ≤ 8 mm
  • Fire-retardant impregnated battens, 20 mm thick, installed horizontally
  • Possible with or without a ventilation cavity
  • Substrate: all substrates of Euroclass A1 and A2-s1,d0 with a thickness ≥ 12 mm and a density ≥ 525 kg/m³
  • Traditional fixing on a timber support structure

With this solution, it has never been easier to choose sustainable, natural and fire-safe building with wood – without compromising on design freedom.

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Plus Line profile and bespoke solutions

Within our range, two boards from the Plus line profile are suitable for fire-retardant open-joint cladding with traditional fixing. In addition, we offer made-to-measure solutions to align your project perfectly, both technically and aesthetically, with the requirements of reaction-to-fire class B.