Cross-Laminated Timber (CLT): Features and Benefits

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Cross-laminated timber (CLT) is an engineered wood product manufactured by stacking and gluing kiln-dried lumber in perpendicular layers. CLT is quite popular in Europe and stands out for its strength, appearance, versatility, and sustainability. 

CLT is nowadays seeing applications in the construction industry as it is a lightweight material, and builders find it to be an affordable building material.

This article discusses the main features and benefits of cross-laminated timber in the construction industry.

Features of Cross Laminated Timber (CLT)

• CLT consists of planks of sawn, glued, and layered wood, where each layer is oriented perpendicular to the previous layer. 
• CLT manufacturing process involves lumber selection, defect removal, cutting, adhesive application, layering the panels, and assembly pressing. The layering process is repeated until the desired thickness is achieved. Typically it goes to three, five, or seven layers. 

• Each layer of CLT is placed perpendicularly to improve structural integrity in both directions. Hence, CLT possesses higher tensile and compressive strength.
• CLT product fabrication has high precision. This helps increase the builders' confidence in the planned project dimensions. 
• CLT panels are assembled and cut into the desired dimension by foreseeing all the joints, openings, and drills specified in the design.

• CLT panels function as walls, furniture, ceilings, and roofs. It is well-suited for multi-story, taller wood construction. 
• CLT compared to other mass timber products, can be topped with concrete to form timber concrete composite (TCC). TCC is a hybrid system that helps reduce cross-sections, increase span, and lessen noise transfer and vibrations.
• In CLT wall panels, the lumber in outer layers is oriented up and down to maximize its vertical load capacity. Likewise, for floor and roof CLT panels, the outer lumber layers run parallel to the direction of the longer span.
• Unlike other wood products, a properly installed and maintained CLT does not rot or mold. 
• CLT elements are protected using sealant, coatings, and flashing to avoid direct contact with moisture.
• The 2015 International Building Code (IBC) and 2015 International Residential Code recognize cross-laminated timber products that are manufactured according to the ANSI/APA PRG-320: Standard for Performance Rated Cross-Laminated Timber. The 2015 IBC code specifies the required size of CLT that is recommended for Type IV buildings. The 2021 IBC approves CLT for buildings up to 18 stories in Type IV-A, IV-B, and IV-C.

Benefits of Cross-Laminated Timber (CLT)

1. CLT construction is lighter and hence requires a less expensive foundation.
2. CLT construction demands less labor.
3. CLT construction is a quick and dry process. Therefore, it consumes less time.
4. CLT chars naturally in fire and forms an outer protective layer.
5. It is a sustainable building material.
6. CLT provides a dry and clean construction site.
7. CLT construction produces less waste.

Disadvantages of Cross-Laminated Timber (CLT)

1. Standard codes and regulations limit the maximum height of building construction using CLT. 
2. CLT is not flexible for future renovation of buildings.
3. CLT wall panels come without wall cavities, increasing the cost of electrical, plumbing, and other services.
4. CLT manufacturing units are few in number, resulting in a higher material transportation cost.

Most of the demerits of CLT decrease with the increase in its supply and demand. With demand, design expertise increases, improving its design flexibility. 

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