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CLT by Stora Enso

Cross-laminated timber (CLT)

Building the future with cross-laminated timber

Cross-laminated timber (CLT) is a mass timber product that can replace concrete and steel in modern construction. As buildings become more sustainable and timber structures grow larger, CLT has become a popular solution for floors, roofs, walls, and stairs due to its strength, appearance, and versatility.

Photo: Belén Imaz/ÁBATON Arquitectura/Madergia

What is CLT?

CLT is made from several layers of solid wood panels bonded with a structural adhesive at alternating right angles. It is ideal for large floor, roof, and wall elements, where mass timber can significantly reduce CO2 emissions compared to concrete and steel.

Why CLT by Stora Enso?

Cross-laminated timber is well known for its strong load-bearing qualities. It is a sustainable alternative to concrete and steel thanks to its acoustic, fire, seismic and thermal performance. CLT by Stora Enso is available from PEFC or FSC-certified softwood. 

CLT by Stora Enso that is customised and delivered just-in-time (JIT) is part of our Sylva™* kit, where it can be used in a variety of applications:

*Sylva™ by Stora Enso is currently only available in Europe and Australia.

Image gallery

25 King Street, Brisbane, Australia
25 King Street, Brisbane, Australia
Photo: Lendlease, Stora Enso Partner: Lendlease, Developer: Impact Investment Group, Architect: Bates Smart
CLT interior in Waldchalets, Brandnertal, Austria
CLT interior in Waldchalets, Brandnertal, Austria
Architect: architekturhandwerk, Developers: The Durnwalder family, Year: 2020, Photo: Günter Richard Wett
Sylva CLT stairs at Haltia Nature Centre, Finland
Sylva CLT stairs at Haltia Nature Centre, Finland
Photo: Vessi Hämäläinen, Architect: Arkkitehtitoimisto Lahdelma & Mahlamäki, Main contractor: YIT Rakennus Oy
Camino de la Huerta, Spain
Camino de la Huerta, Spain
Photo: Belén Imaz, Architect: ÁBATON Arquitectura, Stora Enso partner: Madergia
CLT by Stora Enso
CLT by Stora Enso

How is CLT by Stora Enso manufactured?

Technical product description

CLT by Stora Enso is made of at least three single-layer panels that are bonded together with high-strength adhesive at a right angle. Each layer consists of a set of strength-graded boards that are finger-jointed and bonded together edge to edge. When these strong and stiff layers are bonded and pressed together, they form CLT panels that can be up to 16 m long.

CLT by Stora Enso technical product description

Benefits of designing and building with CLT

All CLT products

  • Cut emissions by up to 70%, compared with concrete and steel

  • Rapid assembly and construction on-site saves time and can lower total costs

  • Strong, stiff, stable and can handle transfer load in two directions

  • Achieve good thermal and sound insulation, and create a comfortable and healthy indoor climate

  • Our Sylva CLT applications can provide adequate fire resistance to meet fire regulations

  • A range of visual grades allows you to experience the real natural look and feel of wood

  • Strong, robust, visually appealing, and CE-marked building components ETA-14/0349

  • Bespoke and prefabricated building products delivered just in time (JIT) to a construction site

  • Save up to 10% more living space

Sylva CLT Floors, Roofs and Walls

  • Can take on very high loads compared to timber frame walls, making them ideal for mid-rise buildings

  • Sylva CLT Floors and Roofs are the slimmest flooring option amongst wood alternatives for short to medium spans

Sylva CLT Stairs

  • Prefabricated as one element for rapid installation and instant access to the working level

  • Replaces the need for temporary construction stairs

  • Cut to precision with no forming and curing time required 

  • Perfect fit in wooden construction—delivered at the same time as other elements and installed by the same tradespeople

Applications

CLT by Stora Enso applications

Discover the possibilities of mass timber with our 3D tool

Browse building concepts

Product range and features

Product types

CLT - type C

The top layers are at right angles to the production length of the panel. Most often used for walls.

 

CLT C panel 

Standard variants

CLT type C is available in 3 or 5 layers

Max length: 16 m

Max thickness: 160 mm

Max width: 2.95 m *

Charged widths

2.25, 2.45, 2.75, 2.95 m

* Larger dimensions can be made available upon request. Please contact your local sales representative for more information

CLT type C

The grain direction of the cover layers is always parallel to the production widths.

Thickness [mm] Type [-] Layers [-] Variant [mm]
C* L C* L C* L C*
60 C3s 3 20 20 20
80 C3s 3 20 40 20
90 C3s 3 30 30 30
100 C3s 3 30 40 30
120 C3s 3 40 40 40
100 C5s 5 20 20 20 20 20
120 C5s 5 30 20 20 20 30
140 C5s 5 40 20 20 20 40
160 C5s 5 40 20 40 20 40

* Sanding direction is perpendicular to the grain

CLT - type L

The top layers are parallel to the production length of the panel. Most often used for floors and roofs.

CLT L panel 

Standard variants

CLT type L is available in 3, 5, 7 or 8 layers

Max length: 16 m

Max thickness: 320 mm

Max width: 2.95 m *

 

Charged widths

2.25, 2.45, 2.75, 2.95 m

* Larger dimensions can be made available upon request. Please contact your local sales representative for more information.

CLT type L

The grain direction of the cover layers is always perpendicular to the production widths. 

Thickness [mm] Type [-] Layers [-] Variant [mm]
L C L C L C L
60 L3s 3 20 20 20
80 L3s 3 20 40 20
90 L3s 3 30 30 30
100 L3s 3 30 40 30
120 L3s 3 40 40 40
100 L5s 5 20 20 20 20 20
120 L5s 5 30 20 20 20 30
140 L5s 5 40 20 20 20 40
160 L5s 5 40 20 40 20 40
180 L5s 5 40 30 40 30 40
200 5Ls 5 40 40 40 40 40
160 L5s-2* 5 60 40 60
180 L7s 7 30 20 30 20 30 20 30
200 L7s 7 20 40 20 40 20 40 20
240 L7s 7 30 40 30 40 30 40 30
220 L7s-2* 7 60 30 40 30 60
240 80 20 40 20 80
260 L7s-2* 7 80 30 40 30 80
280 L7s-2* 7 80 40 40 40 80
300 L8s-2** 8 80 30 80 30 80
320 L8s-2** 8 80 40 80 40 80

* Cover layers consisting of two lengthwise layers

** Cover layers and inner layer consisting of two lengthwise layers

Sylva CLT Stairs

Our CLT comes prefabricated and ready for installation. The waist of the stairs is made of standard C or L-type panels and the stair treads are formed from non-loadbearing transverse layers which makes the stairs more robust on the building site. With very little exposed end-grain, CLT stairs have enhanced resistance to damage and moisture.

CLT stairs can be processed into almost any shape, please contact your local sales representative for more information.

 

CLT Stora Enso stair type 1

 


Surface qualities

CLT by Stora Enso is available in three different surface qualities. Please note that visual quality is only available on the soffits (underside) when applied to Sylva CLT Stairs.

View surface quality chart

Non-visual quality (NVI)

Suitable for when the CLT is not visible or when it will be covered with gypsum, plasterboard, or any other material.

Visual quality (VI)

Best possible surface quality for when the CLT will be exposed and featured as part of the interior design of the building. This grade is commonly used in public buildings, schools, or homes.

Industry visual quality (IVI)

A surface quality suitable for leaving exposed, but not with the most demanding visual requirements, for example, up high on a ceiling. Often this solution is chosen as it is more economical and delivers the same structural qualities.

Reference projects

Donau Lodge
Photo: Stora Enso

Donau Lodge hotel

Ybbs an der Donau, Austria

Learn more
Wolertstetter house
Photo: Thomas Rudolf

Wolferstetter house

Dorfen, Germany
Learn more
Arboretum
Photo: WO2

Arboretum

Nanterre, France

Learn more
Green House
Photo: Jim Stephenson Photography

The Green House

London, UK
Learn more

Browse over 500 wooden buildings and get inspired

Explore references

Technical product data

Key data

Service class Service class 1 and 2 to according to EN 1995-1-1
Product certification CE-marked with ETA 14/0349
Strength class C24 maximum 10% C16 permitted according to ETA (C24 maximum 10% C16 permitted lamellas)
Moisture content 6% to 15% according to EN 13183-2
Wood species Spruce (pine, fir, stone pine/larch and other wood types on request)
Weight/density 490 kg/m3Please note a different density may be declared depending on the need (structural design, transportation, erection etc.)
Reaction to fire class Sylva CLT Walls: Euroclass D-s2, d0
Sylva CLT Floors and Roofs: Euroclass D-s2, d0
Resistance to fire, charring rate

Walls: Cover layer 0.63 mm/min | More than cover layer* 0.86 mm/min

Floors & roofs: Cover layer 0.65 mm/min | More than cover layer* 1.3 mm/min

According to ETA 14/0349

* More than cover layer 1.3 mm/min until 25 mm of charring. Afterwards, the charring rate of 0.65 mm/min on floors only applies up to the next glue line.

Airtightness CLT is airtight according to EN 12 114
Thermal conductivity 0.12 W/(mK) according to ETA 14/0349
Vapour permeability 50 (dry) to 20 (wet) accoding to EN ISO 10456

Adhesives and emissions

The surface and finger joints are bonded with a polyurethane adhesive (PUR) that is approved for load-bearing and non-load-bearing components indoors and outdoors according to the EN 15425 classification. The narrow side is bonded with an EPI or PUR adhesive.

The formaldehyde-free adhesives that we use do not pose a health hazard and the quantities are reduced as far as possible in compliance with the necessary requirements resulting in a fraction of glue at 1%. This all results in very low volatile organic compounds (VOC) levels where CLT meets the most demanding indoor climate requirements.

Fire performance

CLT by Stora Enso can meet fire regulations and has natural fire-resistant properties thanks to the unique charring properties of wood. When timber is exposed to heat, it goes through a thermal breakdown process and a layer of char forms on its surface. Wood has around a 10–12% moisture content and when it ignites, the moisture evaporates, and the charring process begins. This charred layer acts as a natural insulator which protects the inner core. 
 
The surviving structure in the uncharred inner core remains relatively unaffected, maintaining its structural strength and stability. Typically, a wood structure can remain stable for up to two hours when exposed to a fully developed fire. 
 

Tolerances

CLT by Stora Enso is manufactured in modern, factory-controlled environments and cut to size with highly accurate CNC processing. Exceptional size accuracy minimises the need for remedial work when the prefabricated elements are delivered on site, which speeds up the building process and reduces construction costs. 

Element length  +/- 2.0 mm
 Thickness  +/- 1.0 mm
 Width  +/- 2.0 mm

Dimensional stability

Because CLT is cross-laminated, the effects of swelling and shrinking from changes in moisture content are minimized. Standardized values are:

 Direction  % of shrinkage or swelling per % moisture change
 Grain direction  +/- 0.02-0.04
 Cross grain direction  +/- 0.24

Calculatis: a state-of-the-art timber design tool

Start designing with Calculatis

Sustainability

Emission comparison between CLT and concrete

Below is a CO2 eq. emissions comparison* between a typical external wall structure made from CLT and one made from concrete. The result speaks for itself. Manufacturing the CLT wall structure emits significantly less CO2 eq., but it also stores carbon, locking it in the building for decades.

 Emission comparison CLT by Stora Enso wall

The compared wall structures are as follows:

External concrete wall assembly, U-value 0.18 W/m²K

Concrete wall

  • Reinforced concrete 200 mm
  • Insulation with wood studs (timber) 250 mm
  • Plasterboard 9 mm
  • Facade up to design

 

External CLT wall assembly, U-value <0.17 W/m²K

CLT wall

  • Gypsum 18 mm
  • CLT 120 mm (Stora Enso)
  • Plastic vapour control layer, 0.2 mm
  • Insulation 150 mm
  • Insulation 50 mm
  • Facade up to design

 

Assumed building: European 3–8 storey residential building

 

The dataset used for this comparison:

  • Build-ups - typical European, equivalent build-ups from One Click LCA®—automated life cycle assessment software
  • CLT—Stora Enso data from the International EPD® system
  • Other materials—generic data from One Click LCA

 

* Comparison of the CO2 eq. emissions per m² of the product carbon footprint (modules A1-A3 greenhouse gas emissions associated with materials and construction processes up to practical completion). Does not include the CO2 eq. sequestered in the installed products at practical completion. 

Low-impact manufacturing process

Stora Enso is a global leader for low carbon impact in our manufacturing processes. CLT by Stora Enso is produced with only renewable electricity in our production units in Austria and CO₂ fossil-free energy in our Swedish production units.

Sustainability at Stora Enso

View EPD for CLT by Stora Enso

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