Cross Laminated Timber (CLT) - Is the Building Method of the Future? - Overview and SCIA Engineer Implementation

Sep 15, 2026

Cross laminated timber (CLT) is a structural wood product made from at least three layers of boards glued alternately at 90°, creating a material praised for environmental, aesthetic, and energy-related benefits. The article explains CLT standardization progress through Eurocode 5, expected to integrate CLT checks around 2025, and outlines practical applications for floors, roofs, walls, and ribs. It further covers orthotropic modeling, stiffness-parameter calculation using Mindlin plate theory (including bending, shear, torsion), and how to input and verify CLT plates in SCIA Engineer.

LanguageEnglish

CategoryTechnology

FormatPDF

Pages5

Reading Time13 min

AccessFree to download

Cross laminated timber (CLT) overview

Structure and manufacturing details

Standardization and Eurocode 5 integration

Application possibilities in buildings

Orthotropic behavior and mechanical modeling

Orthotropy from 0° and 90° load-bearing directions

Mindlin plate theory for stiffness parameters

Guideline values and correction factors

SCIA Engineer workflow

Modeling CLT as an orthotropic plate

Checking using internal forces and calculations

Cross laminated timber (CLT): the building method of the future? Cross laminated timber (CLT) are flat solid wood products that can be used as structural elements. Thanks to its favorable environmental, aesthetic and energy properties, it is sometimes called the material of the future. The innovative board-shaped product with a laminated structure and interesting physical-mechanical properties consists of at least 3 board layers glued alternately at 90 degrees to each other. The individual boards are mainly 40 mm to 300 mm wide and 6 mm to 45 mm thick. CLT boards are nothing new, they have been produced since 1995 but have not been included in standards until now. Their use in the construction industry was regulated by technical guidelines at European level (ETA: European Technical Assessment) . With the second generation of Eurocode 5, CLT will immediately become part of that same standard, so that structural engineers finally have a way to design and test such structures in accordance with the standard. In the draft version of the new Eurocode 5, expected around 2025, CLT is woven into every check (where applicable) of the standard. The application possibilities of CLT plates are quite broad. The load-bearing properties can be used to act as: 􀂃 Floor element 􀂃 Roof element 􀂃 Wall element 􀂃 Rib-element of a floor 􀂃 ... CLT panels are orthotropic because the load-bearing properties are different in the two directions (0° and 90°) . This is a direct consequence of the number of plates and the positioning of the plate elements in a respective direction. The figure below illustrates the orthotropy using the bending stresses in both directions (0° = main bearing direction, 90° secondary bearing direction): For the bending stresses, only the layers oriented in the respective direction are taken into account. The layers oriented in the other direction act as spacers and are only loaded on shear in the main load direction. CLT in SCIA Engineer Until now there is no check for CLT panels in SCIA Engineer, because of the lack of guidelines in the current Eurocode 5. They can be modelled as an orthotropic plate to take their stiffness into account in the model. Afterwards they can be checked (e.g. using Excel sheets) based on the internal forces which are available after the analysis. The calculation of the orthotropic parameters can be done as follows based on the Mindlin plate theory that accounts for shear force deformation via D44 & D55: Plate stiffness parameters (bending and shear) Bending stiffness in the x-direction: 􀜦11 = 􀮾􀵫01,􀳐􀰔􀳌􀳣,􀳙􀳤􀯂~~ ~~0􀰔􀳤,􀳙,􀳐􀳤 ; in practice: 􀜦11 = 􀜧0,􀯠􀯘􀯔􀯡 ∗ 􀜫0,􀯡􀯘􀯧 Bending stiffness in the y-direction: 􀜦22 = 􀮾0,􀳘􀳐􀳌􀳙 ∗􀯂90,􀳙􀳐􀳟 ; in practice: 􀜦22 = 􀜧0􀯠􀯘􀯔􀯡 ∗ 􀜫90 􀯡􀯘􀯧 􀵫 1−􀰔 􀳣,􀳤 ∗􀰔􀳤,􀳤 􀵯 , , Bending moment influenced by transverse strain: 􀜦12 = 􀜦21 = 􀶥􀟥􀯫,􀯬 ∗ 􀟥􀯬,􀯬 ∗ 􀜦11 ∗ 􀜦22 ; in practice (no Poisson effects): 􀜦12 = 􀜦21 = 0 Torsional stiffness: 􀜦 33 = 􀝇 􀯧􀯪􀯜􀯦􀯧 ∗ 􀜩0,􀯠􀯘􀯔􀯡 ∗ 􀯕~~ ~~∗1􀯗23 Shear stiffness: 􀜦44 = 􀰑10,􀳥 ∗ 􀜩0,􀯠􀯘􀯔􀯡 ∗ 􀜣 0,􀯡􀯘􀯧 Shear stiffness: 􀜦 55 = 􀰑190,􀳥 ∗ 􀜩0,􀯠􀯘􀯔􀯡 ∗ 􀜣 90,􀯡􀯘􀯧 With: 􀜧0,􀯠􀯘􀯔􀯡 : Mean E-modulus in the main bearing direction (0°) 􀜩0,􀯠􀯘􀯔􀯡 : Mean G-modulus in the main bearing direction (0°) 􀟥􀯫,􀯬 & 􀟥􀯬,􀯬 : Poisson ratios In practice, one ignores the Poisson effects, as if planks are 'unglued' next to each other in the same plane 􀃆 􀟥􀯫,􀯬 = 􀟥􀯬,􀯬 = 0 􀜫0,􀯡􀯘􀯧 : Net moment of inertia in the main bearing direction (0°), i.e. only the layers in the main bearing direction should be taken into account using the formula below: 􀯡 􀯡 􀜫0,􀯡􀯘􀯧 = 􀷍 􀜧􀜧􀯜􀯖 ∙ 􀜾~~ ~~∗1􀝀23􀯜 + 􀷍 􀜧􀜧􀯜􀯖 ∙ 􀜾 ∗ 􀝀 􀯜 ∗ 􀜽 2􀯜 􀯜 = 1 􀯜 = 1 Where: Ei: E-modulus of the respective layer Ec: Reference E-modulus (if all layers have the same E-modulus E_i/E_c =1 ) b: For the width, a unit width of 1 m can be used di: Thickness of the respective layer ai: Distance between the centre of gravity of the whole CLT panel and the centre of gravity of the layer in question 􀜫90,􀯡􀯘􀯧 : Net

FAQs

What is cross laminated timber (CLT) and how is it constructed?

CLT consists of flat solid wood boards with laminated layers glued alternately at 90° to each other. It uses at least three board layers, with typical board widths and thicknesses suited for structural elements.

How does Eurocode 5 affect the use and design of CLT structures?

CLT is produced since 1995 but was previously not fully included in standards. With the second generation of Eurocode 5, CLT checks are expected to be integrated (draft around 2025), enabling structural engineers to design and test structures according to the standard.

Why are CLT panels treated as orthotropic, and how is SCIA Engineer used for checking?

CLT panels are orthotropic because load-bearing properties differ between the 0° and 90° directions due to layer positioning. In SCIA Engineer, CLT can be modeled as an orthotropic plate, using calculated stiffness parameters and then checked using available internal forces (e.g., with external calculations such as spreadsheets).

Sep 15, 2026

Upload by Alex Sinclair