Cross Laminated Timber (CLT)

Author : Anushtha Moolchandani

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“Our biggest challenge in this new century is to take an idea that seems abstract – sustainable development - and turn it into a reality for all the world's people”

-Kofi Annan

Introduction

Innovation and evolution of sustainable creation plays a colossal role in future development of built environment. Cross laminated timber is one such “Green” alternative invigorated by government to be inclusive in sustainable development and climate change mitigation strategies. (Gong, 2019) Initially, in early 20th century market was conquered by reinforced concrete to a great extent. Although, lumber has revived in the market over the past decade replacing mineral-based building materials. Commercial launch of MTP’s (Mass timber products) is a vital reason to recapture the market shares. Green low-carbon engineered timber product is extensively used in Europe and North America. (Gong, 2019), (HaoLi, 2019)

1.1 What is CLT?

-Cross laminated timber (CLT) is contrived structural panel or lumber board (kiln dried and trimmed) aligned crosswise at right angles on top of each other with the help of adhesive forming multiple layers (usually 3,5 or 7). (Roberts, 2020) (Gong, 2019)

Figure 1: Depiction of CLT board alignment

-This method of CLT makes copious use of material features i.e., high tensile strength of the wood in the direction of the grain (longitudinal layer) and the high compressive strength in the opposite direction (transverse layer) in order to gain higher mechanical properties and strength.

(Gong, 2019), (HaoLi, 2019)

Figure 2: A generic CLT made of timber.

1.2 How is CLT an innovative sustainable alternative? If CLT is compared to conventional building practices then it is much more justifiable and viable. Factors supporting this statement are as follows:

• ENERGY CONSUMPTION: Low

• EMISSION: Statistically CLT stores more CO2 during manufacturing process thus emitting lesser amount of greenhouse gasses.

• EFFICIANCY: Viable way to improve energy efficiency.

• RENEWABILITY: As lumber is inexhaustible and possess absolutely no harm to the external environment this material is the precise candidate for forthcoming construction. (Mallo & Espinoza, 2014) (Haibo Guo, 2017)

Table 1: LIFE CYCLE OF CROSS LAMINATED TIMBER [ CLT] (Haibo Guo, 2017)

1.3 Analysis of BENEFITS and DETRIMENTS of CLT as a building material/ construction process

PROS

• Saves time as construction duration is quite less as compared to other methods.

• Light weight panels can be transported and installed with utmost ease.

• Limited site skills are required as CLT is pre-fabricated.

• Renewable and present in abundance 

• Custom dimensions with varied panel size depending on the manufacturer is the biggest advantage of CLT.

CONS

• CLT is not at all economical as compared to the materials used in conventional construction.

• External cladding and insulation are necessary.

• Can lead to shear failure and excessive deflection if not bonded properly.

• Lack of awareness: Hardly few designers know about this technique and are ready to work.

• CLT comes with height code restrictions .

(Gong, 2019)

1.4 PLYSCRAPER: Example of CLT construction

Table 2: SPECIFICATION OF CLT STRUCTURE IN CHAROLETTE, USA (Bahrani, 2018)

Figure 3: ELEVATION OF PLYSCRAPPER IN USA (Bahrani, 2018)

Figure 4: FRAME TYPE USED IN PLYSCRAPPER IN CHAROLETTE, USA (Bahrani,2018)

ENVIRONMENTAL CONSIDERATIONS FOR SUSTAINABILITY

• Resource-efficient throughout the building’s life cycle.

• LEED 2009 Green Building Rating System used to evaluate the conservational performance.

• Certified design with monetary, ecological, and social benefits

• Environmental Goal: condense the overall impact of the structure.

1. Lower functional costs and surge asset value.

2. Diminish waste sent to landfills

3. Energy and water preservation

4. More healthful and productive environments for building occupants (Bahrani, 2018)

Figure 5: COMPARISION OF WOOD CONSTRUCTION WITH MINERAL BASED MATERIAL CONSTRUCTION

(Bahrani, 2018)

1.5 CONCLUSION: ANALYSIS AND JUSTIFICATION OF DATA DEDUCED FROM RESEARCH

Cross laminated timber falls under the category of SYSTEM INNOVATION since it is a combination of PRODUCT and PROCESS innovation. CLT or Mass timber is surely an alternative for forthcoming construction industry. The benefits of CLT outweigh the limitations. Though there should be a deep consideration of certain points while choosing this type of technique such as:

1.Fire bearing capacity

2.Limited designers’ availability

3.Height restrictions

4.Hybrid wood construction offers better strength and stability

5.Time and Cost factors

6.Sustainability

Also, CLT is a complete package as it constitutes structural and non-structural elements (internal and external). Moreover, lumber is collected from decayed trees which are responsible for carbon emission so it is better to use it and plant a new tree.

References

1.Meng Gong (April 12th 2019), Submitted: September 11th 2018 Reviewed: March 12th 2019 Published: April 12th 2019

Lumber-Based Mass Timber Products in Construction, Timber Buildings and Sustainability

Giovanna Concu, IntechOpen

DOI: 10.5772/intechopen.85808.

Available from: https://www.intechopen.com/books/timber-buildings-and-sustainability/lumber-based-mass-timber-products-in-construction

[Last accessed date: 4 February,2021]

2. HaoLi12Brad JianheWang2PeixingWei23LibinWang1 (feb,2019) quotes [Brandner R., Flatscher G., Ringhofer A., et al. (2016)]when they say that “secondary referencing is important”.

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Cross-laminated Timber (CLT) in China: A State-of-the-Art

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[Last accessed date: 4 February,2021]

3. David Roberts  (Jan 15, 2020, 10:30am EST)

The hottest new thing in sustainable building is, uh, wood

The many, many benefits of using wood in place of concrete and steel

VOX

Available from: https://www.vox.com/energy-and-environment/2020/1/15/21058051/climate-change-building-materials-mass-timber-cross-laminated-clt

[Last accessed date: 5th February,2021]

4. Mallo, M.F.L.; Espinoza, O.A.

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5. Haibo Guo 1 , Ying Liu 2 , Wen-Shao Chang 2 , Yu Shao 1 and Cheng Sun 1

(Received: 13 January 2017; Accepted: 15 February 2017; Published: 17 February 2017) quoted by Asia, F.  (26 November 2015) in Understanding Cross-Laminated Timber when they say that “secondary referencing is important”.

Energy Saving and Carbon Reduction in the Operation Stage of Cross Laminated Timber Residential Buildings in China

Page no.1-5

Available online: file:///C:/Users/Anushtha/Downloads/sustainability-09-00292%20(1).pdf

[Last accessed date: 6th February,2021]

6. Bahrani, Babak & Saunders, Christina & Shabanian, Milad & Braxtan, Nicole & Rockwell, Scott & Zhou, Aixi. (2018).

High-Rise Residential Building using Cross-Laminated Timber (CLT)- Charlotte 9th Street Tower- United States Case Study.

Page no.6-27

Available from: https://www.researchgate.net/publication/324149760_High-Rise_Residential_Building_using_Cross-Laminated_Timber_CLT-_Charlotte_9th_Street_Tower-_United_States_Case_Study

[Last accessed date: 6th February,2021]