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

19/06/2026

Vertical timber cladding with open joints in reaction-to-fire class B: Carpentier now makes it possible too, with traditional fixing and the accompanying reaction-to-fire classification reports.

Reaction-to-fire classification reports for open-joint cladding with traditional fixing.

Since the change in the regulations on the reaction-to-fire class of timber cladding last summer, we have already held 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 spacing of 8 mm. This aesthetic and fire-retardant façade solution has become reality thanks to a clever combination of fire-retardant treatment with polymers, considered design and careful installation. As a result, you can now apply open-joint 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. However, this is actively being worked on.

Technical requirements for reaction-to-fire class B

With this solution, you choose sustainable, natural and fire-safe building with wood, without compromising on design freedom.

  • 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

Reaction-to-fire class B without fire-retardant treatment

Are you looking for a closed façade in reaction-to-fire class B without fire-retardant treatment? Then thermo bamboo is a strong choice. Our closed façade profiles in HOTwood bamboo achieve reaction-to-fire class B-s1,d0 naturally. You will find them, together with all other profiles in reaction-to-fire class B, on our reaction-to-fire class B cladding page.

Plus Line profile and made to measure

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

Prefer an invisible fixing?

With Pyroclip, you also achieve reaction-to-fire class B with QuickClip®, our invisible fixing, and open joints up to 30 to 35 mm. You will find more information on our reaction-to-fire class B cladding page.

Help shape your design with our wood expertise

From initial concept to technical detailing: our experts are happy to support you with targeted advice on timber solutions that suit the architecture, materiality and ambition of your project.