CLT is a prefabricated timber panel product made up of layers of sawn lumber that are laminated together using structural adhesives. The idea of laminating timber was famous for many years but never as a major support-element for tall structures.
CLT, when developed in Austria and Europe in the 2000’s, focused on the sustainability of residential construction. Today, it has proved potential in playing a similar role as concrete and steel have done in the years past. What then should once consider when using Cross Laminated Timber?
1. Laminated timber should have odd number of panels of either 3, 5 or 7 glued together to minimize warping, cupping, and twist. The idea of laminating an odd number of panels which have the major layers at the edge with their grids running in the same direction.
2. All Cross Laminated Timber panels are joined together using glue without any screws, nails or mechanical fixings. If used, these would become points of weakness to the timber. The most commonly used glue is a polyurethane adhesive
3. The direction of the altered laminations is important and is dictated by the intended use. If intended for walls, the layers should be vertical or transverse, while for floors and ceilings, they should run horizontally
4. If the design of the CLT used in a structure has enough material/layers, there would be no need for lintels along the window and door openings. Structural beams can also be excluded in this case.
5. Excessive trimming of the CLT in provision for door and window openings should be minimized as this would reduce its structural properties. Therefore, the positioning of the doors and windows should be well considered and spaced during the architectural designing of a structure.
1. The construction must be planned out early to reduce the building times as much as possible. The benefits of prefabricated building elements and short building times should be maximized in order to reduce the risks of building with CLT.
2. Incase rains above 40 mm is expected or rather if the building time is expected to be long, a roof cover will be required. Having known that a timber is vulnerable to water/moisture, a CLT building should be protected from rain regardless of location and time of year. A simple roof cover or rain screen can be built to divert rain from the CLT surfaces thereby protecting them from wetting. This could also be the use of over-pressurized joints and gaps and tape on transitions between walls and floors, combined with some rain protection that do not collect or trap water.
3. If the surrounding environment has an annual average of relative humidity above 80 % or an annual rainfall beyond 1200 mm, a building cover should be provided to boost the drying process of the timber. Construction in a protected environment saves the structure from various possibilities of damage during construction process.
4. Free water or snow on the CLT surfaces must always be avoided. Snow must be removed directly so as not to become a moisture source.
5. Insulation is most effective if done on the external faces of the panels as a semi-rigid fibre insulation or as rigid boards. This reduces the effects of changing temperatures. The proposed finishes can then be applied on the insulated layer.
6. When joining the timber beams and column joints, steel brackets and their respective fasteners are used. Connectors define the behavior of the CLT wall in terms of strength, stiffness, deformation capacity, and energy dissipation.
1. Every construction site should have an area designated for CLT storage. This should be a clean and level surface with good drainage.
2. Never store panels directly on the ground or in standing water Ensure that the storage and staging area has adequate air flow to prevent fungal growth.
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