Solution > Fire retardant treatment

Reaction to fire class D-s3,d1

The reaction to fire of solid wood that has not received a fire retardant treatment depends on the type of wood, the density of the wood, the thickness of the profile and the method of installation.

When fire rating D-s3,d1 is required, no fire-retarding treatment is needed when below terms are met:

  1. profiles with a minimum thickness of 18 mm
  2. wood species with a minimum mean density of 390 kg/m³
  3. closed cladding (or open cladding with larch under certain conditions)


It is important that these cladding profiles are positioned at a back wall/substrate with fire rating A1 or A2 = non-flammable.

Solutions one

Facade construction reactio to fire class D-s3,d1*

  1. Insulation material, at least A2-s1,d0 with a minimal density of 10 kg/m3. Where the requirements of A2-s1,d0 (e.g. PUR) are not met, a protection plate K2 10/K2 30 or EI 15/EI 30 must be provided.

  2. Moisture barrier.

  3. Ventilated air cavity + attachment system (e.g. spruce or pine timber).

  4. Closed facade cladding with boarding at least 18 mm thick, made of timber with a minimum density of 390 kg/m³.

    *Source: Buildwise

Info One

Additional explanation*

Decision 2006/213/EG specifies the fire rating that –under certain conditions – applies for solid wood cladding without further tests (see table B). We would like to point out that according to test and classification reports, cladding made from strips of cedar (WCR) with a thickness of 18 mm and a mean density of more than 390 kg/m³ has fire rating D-s2,d0. The installation conditions are identical to those from the table. Wooden cladding that satisfies the conditions from the decision (see table B) and cedar cladding meeting above conditions, do comply with the requirements for low buildings as their fire rating (D-s2,d0) is more favourable than the required rating (D-s3,d1).


Minimum average densityMinimum thicknessesInstallation conditions (total/minimum)Fire reaction classMinimum average density
390 kg/m³18/12 mmWith an open rear cavity (*)D-s2, d0391 kg/m³

*The substrate (e.g. insulation) behind the ventilated cavity must belong to at least class A2-s1,d0 and exhibit a minimum density of 10 kg/m³.

Other types of timber cladding also need to meet the requirements for low buildings. In case these claddings do not comply with a decision from the European Commission, a test and classification report will be conclusive. We would like to point out that the installation conditions from the test report must be strictly followed.

I must fulfil the requirements of reaction to fire class B-s3,d1 or C-s3,d1


Technical questions?

Get in touch with our fire retardant expert.

Geoffrey Moerman

Geoffrey Moerman

+32 (0)471 98 22 79

Technical sales advisor Lemahieu Fire Protection® with Burnblock® Ostend