Cross-Laminated Timber (CLT) | CLT Disadvantages and Advantages

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Cross-Laminated Timber (CLT) | CLT Disadvantages and Advantages
cross laminated timber

Introduction

Cross-laminated timber (CLT), also known as X-Lam is an engineered timber product. CLT made by gluing together multiple layers (usually three, five, or seven layers) of solid lumber using a hydraulic or vacuum pressure. Each lumber board placed side-by-side. To make a strong CLT structure, Panel timbers are arranged crosswise to each other at an angle of 90 degrees. Its strong structure is able to bear heavy loads.

The odd number of layers is most common. In the present day, it has become a well-known engineered timber product. CLT is in use around the world. Its demand is increasing day by day in almost every country. 

Full-size walls, floors, and ceilings are build using CLT. It is somewhat similar to Plywood. But uses veneer sheets to make plywood. The thickness of plywood is very thin. While lumber uses to manufacture CLT. There is no doubt that the CLT is stronger than the traditional Lumbar and plywood.

CLT was developed in Germany and Austria in 1990. Which would lead to a new revolution for the sawmill and building construction industry. Initially, it was not very popular, but its production has increased over the years since 2005. CLT used in many countries of Europe and around it. CLT used for small to large construction and now this material has become a need for the industry.

Cross-Laminated Timber Uses

Plato has truly said, “Necessity is the mother of invention”. Cross-Laminated Timber is also one of them. The typical uses of CLT are as load-bearing parts for building frames such as a wall, roof, and many other applications. The use and production of CLT are increasing day by day.

worldwide production volums of CLT
worldwide production volume of CLT

Cross-Laminated Timber uses it on the basis of the number of layers. We will divide it into 3 categories.

#ThicknessNo. of LumberUses
Minimum40 to 51MM3 LayersWalls, Secondary construction 
Standard140 to 160MM5 LayersFloor, Beams, and Roofing
Maximum400 to 500MM11 LayersBridge and Decks
Cross-Laminated Timber

CLT Beams

Beam and Pillar play an important role in building a house. It is essential to be strong. They carry a full roof load. In addition, strong winds and storms also have to be faced. In this case, CLT is much better than traditional wood and other wood materials. Because the hollow and knotted parts of the timber are removed during the CLT manufacturing process.

It is not defective after its manufacture. They become stronger as they come in contact with the glue with the cross structure.

Flooring and Decking

Cross-laminated timber flooring is a durable and better option. It has been in use for many decades. CLT’s cost for materials may be lower than traditional steel or concrete. Some floor experts say that to make a better floor, the thickness of the CLT should be at least 4 inches.

Cross-laminated Timber Roof

Cross-laminated Timber Roof
CLT Roof

Cross-laminated Timber has many features such as insulation, optimal air humidity, soundproofing, excellent fire protection, high load-bearing capacity, and earthquake-proof construction. All this goodness makes this construction material better for roof use. It is also used with glulam timber as a hybrid construction.

Walls

Multiple layers use with CLT for such as weather protection(on the outermost wall), insulation, CLT Panel, and Internal Lining(From the inside). This is very important for external walls.

CLT is an environmental-friendly building material. Its use does not cause any harm. This material is used to reduce energy consumption.

Cross-Laminated Timber
Cross-Laminated Timber

CLT Manufacturing Process

We divide the CLT manufacturing process into the main 9 steps. Each step depends on the next steps. Therefore, it is important that the process of the first step is done properly. So let’s see the CLT manufacturing process.

1. Timber harvesting and debarking

Harvesting and debarking of large logs is the first process. For this process, choosing the right tree from the forest is an essential part. Mainly  Spruce is used to making CLT, but it may include a percentage of Pine or Larch, and possibly hardwood.

Many rules and government conditions are followed for harvestings, such as tree age and species. Debarking is the process of removing bark from wood. In this process, the log is passed through the roller of a large machine. In which there are many granulated blade belts that clean the bark of the log. The most common use of tree bark is to burn it for heating. It can also be used for gardening as compost.

2. Drying

The drying process applies to reduces the moisture content of the wood. Wood expands when it contains moisture and shrinks when it dries. No customer would like to use damp wood. Which will shrink later and spoil the structure of the application. Secondly, when moisture is present in the wood, it is flexible and does not bear much weight.

Kiln for this process Is uses for the drying process. A kiln is a thermally insulated chamber. The temperature of this chamber is maintained to complete the Drying process.

3. Lumber grouping

The grouping process ensures the timber of various categories is grouped together based on lumber quality, size, structural properties, and knots. This process also determines the price of CLT grade.  Lumbar with better structural properties is used for interior application purposes.

4. Cutting and grinding

In this process, the logs of wood are converted into lumber. All lumbar are cut to the proper thickness. The thickness of the lumbar is always higher than the final lumbar. So that even after grinding It remained in the correct thickness.

Large cutting machines are used for cutting. In this machine, several lumbar multiple cuttings can be done simultaneously. This machine has a sharp blade that cuts the wood log. This process must be done very carefully.

After cutting from the large tooth blade, there are remained many cracks and Bulge on the surface of the lumbar. Which is necessary to smooth it before sending it to the next process.  

A grinding machine with sandpaper is used to smooth it. This machine has sandpaper wheels. These wheels rotate continuously. The moving wheel is driven over the lumbar. Due to which a lot of wood powder is extracted from it. The thickness of the board is usually between 5/8 inch to 2 inches and the width ranges from 2.4 to 9.5 inches.

Grinding
Grinding

5. Adhesive Process

In this process, waterproof adhesives are sprayed on the number of members. Polyurethane adhesives (also know as PUR) or phenol resorcinol formaldehyde (PRF) adhesives are used in the production of CLT, finger joints, glulam, laminated logs.

In this process, the lumbar board is passed through a tunnel. The tunnel has many nozzles spry. Which is constantly sprayed with adhesive on wood.

Adhesive-process
Adhesive-process

6. Panel lay-up

After the gluing process. One lumbar is placed on the other lumbar at a 90-degree angle. Lumber boards (usually three, five, or seven) are pasted together in this process. The thickness of each layer of timber typically varies in thickness between

17 mm to 45mm. Thus the thickness of the entire CLT can range from approximately 51 mm to 500 mm.

cross laminated timber structural design
cross laminated timber structural design

7. Heat and Pressure Process

The CLT structure has to bear a lot of weight. For this, it is necessary that all the timber boards should be strongly connected. High pressure is applied to all lumbar in this process. This pressure is higher than that generated by the hydraulic machine. 

The CLT Lumbar is inserted into the machine used for this process. Which is like a vacuum chamber. 100–150 ° C Temperatures and approximately pressures of 700–6000 psi are used for this process.

8. Cutting to CLT panel

After this process is complete, the Cross-Laminated Timber panel almost becomes complete but is still not ready for production. Before that, it is very important to cut it into the right shape and size.

Timber is trimmed from all four sides in the cutting process. This cutting process gives the right shape and size to  Cross-Laminated Timber based on demand and applications.

9. Marketing and shipping

After cutting and finishing CLT panels are ready for production and construction use. In this step, the finished CLT panel reaches from the manufacturing production house to the CLT store. Now the customer can buy the CLT as per their requirement from the local store.

Cross-laminated timber Advantages

High Load Capacity

Cross-Laminated Timber is high load capacity construction material. Due to its great properties, To build heavy construction structures such as beams, bridges, and walls CLT is the best option. It is stronger and durable than other wood construction materials.

High Load Capacity properties do not have benefits for CLT floor panels because the floor does not have to bear a heavy load as wall and roof. But Its High Load Capacity properties are very important. When it is use to beams and roof construction.

Fast Installment

Some customers think that they cannot get the design they want by using the CLT panel. But this is not true at all. We can get all the designs similar to solid wood using CLT panels. But it is also true that in some cases it is difficult for some designers. Some experts say “CLT is six times faster than traditional methods“. It is easy to work with.

Thermal Performance

Good thermal insulation performance and good sound insulation properties are additional benefits of CLT. CLT has a thermal conductivity of 0.13W/mK. In properties of thermal performance, it is better than traditional wood logs, steel, and concrete. This is very beneficial for those regions which have very cold and hot weather. This material has multiple lumbar layers that maintain room temperature.

Its increased performance is due to the adhesive used between lumber layers. A high degree of thermal performance required for the external walls.

Fire protection

CLT wall panels have fire resistance due to their structure. During the fire, a charred layer is formed on the CLT surface, which prevents the oxygen( helps to increase the fire) from the outside. Because of this, the fire does not spread much.

All layer-based construction enables the application of decorative or soundproofing or fireproofing due to the cover layers.

Environmental Advantages

Some test and research results prove that. An average 26.5% reduction in global warming potential has been achieved in CLT buildings compare to concrete and other construction material. Increasing global warming and Environmental problem, It is very beneficial for our environment.

Less waste

It is available in almost every shape and size. The manufacturing company makes it on the basis of different purposes and applications. So, very little waste material comes out using this product.

Cross-laminated timber Disadvantages

Price

Cross-laminated Timber is more expensive than traditional construction such as steel, or concrete. Its price rise depends on many things. Like Transportation, Integration cost, and grade. 

To manufacture CLT panels require a large manufacturing plant. CLT is not manufacturing in many locations. These plants send their material far and wide which makes the transportation charge expensive. CLT Panel requires Large transportation vehicles. So it has a high cost.

The use of CLT increases the electrical and plumbing cost because it is difficult to install electronics and plumbing equipment in this material as compared to traditional material. CLT requires less Maintainance but the maintenance cost is higher compare to traditional wood

Limited Track Record

Cross-Laminated Timber material is still the new material for many countries. Due to its limited track record, it can be difficult for many designers to use.

Another disadvantage is that it has limited flexibility to use. Such as the height limit of construction buildings. So many buildings do not use CTL as build project material. Many people do not want to use new material and less knowledge.

Difficult to Install

Its structure is stronger than traditional wood. But due to its structure, it is difficult to work with some machines and tools.

Many designers and constructors understood that they have faced difficulty with this material during constriction. Which was not the case with traditional material.

Availability

Being a new material, it is not available in many cities and countries. Some countries supply in limited quantities. So that sometimes it is lacking. Many countries and cities have not available perfect size and grade. Which sometimes becomes a problem.

Environmental Impact

It is spreading rapidly and its demand is also increasing. In some counties, flow terms and conditions to harvesting but some country not. To make CLT panels and other engineering materials Rapilly trees are harvest. This is having a bad effect on the environment.

Cross-laminated timber texture

The cross-laminated timber has a yellowish-white texture. It has small knots on the panel. As I mentioned above, CLT is mainly made from Spruce, Pine or Larch, and other hardwoods. There is no change in the texture and properties of this wood during CLT manufacturing. 

The heartwood color of Spruce Pine is reddish-brown, sapwood is yellowish-white. it has straight-grained with a fine to medium texture. 

Conclusion

Cross-Laminated Timber is an excellent engineering construction material. CLT is a great material for the new construction era. It has some flaws as well as some merits. Which I have tried to cover. Even with a few commissions, it is a better material, and hopes that it will improve even more in the coming days.

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