INTRODUCTION TO CROSS LAMINATED TIMBER
Over the years, steel and concrete have been the main elements of every construction, the heart and skeleton of every structure. However, in the abundance of resources, discoveries never come to an end. Timber has previously been used for mainly aesthetic purposes in construction but never as a major building element in a big structure! The idea of laminating timber was famous for many years but never as a major support-element for tall structures.
Cross Laminated Timber, when first developed in Austria and Europe in the 2000’s, focused on the sustainability of residential construction. This was of no doubt a matter of interest to many due to global environmental awareness. Today, it has proved potential in playing a similar role as concrete and steel have done in the years past.
The possibility of using Cross Laminated Timber (CLT) when proposed has been accompanied by extensive research on its economic benefits, environmental benefits and structural integrity.
THE MANUFACTURE OF CROSS LAMINATED TIMBER
CLT panels consist of three, seven or nine layered lumber boards stacked in opposing directions (perpendicular) and glued together to form one complete piece of timber in a press. Usually, low volatile adhesives and finger joints are used for the perfect bonding of the layered boards. With these, lengths up to 16m, widths of up to 2.5m and thicknesses up to 500mm depending on manufacturer.
The CLT panels are then cut to desired shapes and sizes by a machine including window and door openings. The use of these machines reduces wastage and any errors in the required dimensions as per orders made. In the provision of door and window schedules, the accompanying openings can be cut
The different layers embedded in the CLT were carefully thought of to improve its structural properties and also avoid any factors that would reduce its ability to be durable.
- Air/Vapour control layer. Vapour Control Layer is applied at ground level then craned into position.
- Thermal control layer. This layer is usually an insulation. The insulation thickness of each insulation material is determined after analyzing the thermal moisture and energy performance of the proposed insulation material. The insulation material could be a
sealing compound, rubber moulding or sheets of airtight material. An insulated wood timber sheathing is then fixed in the other layers to work as a thermal control layer.
- Water control layer. It is important to protect a building from rain at all locations and at all times. A wet surface may be crucial in summer with respect to moisture transport. All mould indices are higher during autumn cases compare to spring cases. Some protection is better than none, and some type of waxing or coating is believed to be a good alternative for difficult positions. A separate, continuous cover is better than directly applied surface coatings or tape on horizontal surfaces. The risk of condensation and moisture trapping could be mitigated by the choice of cover and allowance for drying
- Weather control layer. It is difficult or impossible to avoid the emergence of microbial growth during construction with CLT without weather protection. Weather protection therefore prevents the growth of moulds and rotting of the CLT used. The mould growth is caused by exposure of the CLT to precipitation in the form of free water. The mould growth is caused by exposure of the CLT to precipitation in the form of free water. It is often invisible and cannot be detected with the naked eye. Detection requires microbiological analysis. Therefore, further research is required to detect any mould growth in a CLT structure.
ADVANTAGES OF USING CLT
1. Cost effective as compared to steel and concrete.
The use of CLT is generally more cost effective than concrete and steel as emphasized below.
Wood is a readily and naturally available domestic resource compared to steel and concrete. There is room for replacing what has been cut thereby promising continuity in CLT production. Timber also being a renewable resource reduces on construction waste.
The use of CLT is accompanied by a reduced material usage in a project. This is because timber is 75% lighter than steel and concrete therefore making a complete CLT structure generally light. This reduces the foundation costs in terms of footing sizes and reinforcements.
In construction, the longer a project takes, the costlier it is in regards to time and money. CLT panels can be assembled and fully manufactured off-site (factory) and easy to transport to the site. Depending on the details of the construction project, CLT can be used to make columns, beams, walls, staircases or floor panels that are later assembled on-site. In either case, the prefabricated CLT elements are compact and easy to transport, making it possible to deliver them even across large distances.
2. Sustainability (Substantial carbon sequestration) benefits
CLT is eco-friendly as it creates a smaller percentage of greenhouse gas emissions as compared to steel and concrete. To a greater advantage, there are various promising vegetation zones world wide which would serve as potential suppliers of Timber towards making more CLT panels. With the use of CLT, there are less carbon dioxide (CO2) emissions as compared to concrete thus reducing greenhouse effects in the atmosphere. Therefore, timber buildings have a lower global warming potential (GWP) than concrete or steel buildings.
WHY CLT NOT STEEL OR CONCRETE?
- Excellent seismic performance due to the strong resistance rendered against seismic waves.
- Improved building envelope thermal performance
- Avoidance of fossil-fuel intensive materials
- Low combustibility characters due to the protective layers instilled during its manufacture
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