A DURABLE PARTNER FOR ECOLOGICAL BUILDING SOLUTIONS
CLT offers a revolutionary response to the various challenges of the construction sector in many different areas:
Exactly replicate what is virtually modeled in BIM.
Building assembly process: up to 60% faster from design to completion.
Less manpower in preparation and on site.
Lean building: a structure where other elements can be added more easily (windows, techniques, etc.).
Acoustics and fire solutions are available.
The effects on EPB and insulation values.
Solutions for building on suboptimal land and on-top of existing buildings.
Circular and Ecological building.
To be able to clarify these different facets in more detail, it is necessary to clarify the properties of CLT.
WHAT IS CLT ?
CLT stands for Cross Laminated Timber. Planks are produced from sustainably managed pine forests. These boards are glued to "single layers" on the side. These single layers are glued crosswise to each other with formaldehyde-free glue, so that the fiber directions of the single layers are perpendicular to each other. This process generates a form-retaining panel called the "master panel". The master panel can be passed through a CNC machine for cutting, milling or drilling. The panels can be used for floors or walls and have different bearing properties depending on their thickness and composition.
CLT can therefore replace the entire traditional structure of a building. With CLT it is possible to build multiple floors. CLT-S has built the highest CLT building in Belgium, consisting of 12 floors. In Norway, Brumunddal, you can find the tallest wooden building to date, consisting of 18 floors, making it a 85.4 meters high structure.
Source: CLT-S project Astor Geel
CLT is sometimes incorrectly compared to timber frame construction or solid timber construction. However, because CLT is dimensionally stable, less interesting properties such as shrinkage and dilatation across the fiber direction of the wood are eliminated. Therefore it can also be used for wider applications.
Further finishing of the building (facade, floors, utilities, etc.) can be done in a similar way.
Because CNC machines can do all kinds of operations, it is also possible to provide passage openings for utilities (HVAC, electrical, plumbing) from the factory. As a product, CLT is therefore revolutionary because the structure can be fully drawn in 3D and then accurately produced to assemble the structure on site. In this way, CLT can ride the wave of the BIM story.
CLT is the first user-friendly and durable material with which a 3D model can be perfectly replicated in reality.
Source: CLT-S Project KOCA, boerding school
Visually, CLT can be applied in various ways. Buildings can look exactly like a traditional building even though CLT is the supporting structure. A non-expert could not see the difference. However, a building can also be designed with visual CLT. There are 2 visual qualities to choose from: industrial visual quality and visual quality. This allows the structure to be shown from the inside. A big advantage of CLT interior walls is that they are solid and do not sound hollow. From a commercial point of view, this is always appreciated.
HOW DOES THIS AFFECT THE BUILDING PROCESS?
If you decide to use CLT for your project, this means that the complete implementation file must be ready before you start building. Once the panels are in production, there is no way back. Because CLT also has other load-bearing properties than traditional materials, it is advisable to opt for CLT from the design phase as a rough building material. As a result, the use of CLT can be optimally incorporated into the design and the cost will therefore be similar or cheaper than other, more traditional building methods.
CLT-S always delegates a team of 3 people to the project:
A project manager supervises the entire process within the construction team and takes care of all communication with the customer.
A 3D modeller draws the production drawings of the structure.
An engineer is responsible for the study of stability, the calculation notes and the detailing of the structure.
Every CLT-S project team knows that it is necessary to play a proactive role in the construction team. New building technology requires a different approach in the preliminary phase and this must be propagated by CLT-S, even though CLT-S is only a subcontractor structure.
The architectural design must take the structure into account. That is why it is good that the stability engineer is immediately involved. After all, the stability study determines the thickness of the CLT panel. Which is also one of the larger cost drivers for a CLT structure.
In order to determine the full cost of a CLT structure, in addition to a structural study, a 3D model must be made with the correct CLT panel thicknesses. This 3D model is then pulled apart to "nest" the different panels in the master panels. In this way the cutting loss can be determined. The cutting loss is therefore the second major cost driver when using CLT.
CLT is completely made of wood and has a linear cost curve. In contrast to concrete that has a smoothing curve because of the fact that the majority of the costs are in the formwork and reinforcement.
The intention must therefore be to use as little wood as possible.
Once the design has been finalized, a structural model will be built by CLT-S. The connection details are drawn by our engineering department and, together with the stability plans and the calculation notes, are submitted for approval by the stability engineer who is responsible for the project. In the structural model, all details (structural, acoustic, quality of vision, window and door openings, etc.) that are important for production are included. Once the structural model has been finalized, the saving proposals for the utilities are drawn in.
Lean building is perfectly possible because CLT structure is assembled and not built. The assembly can be virtually simulated so that it is also optimized during construction time.
Because all panels are labeled, you can scan them and see in a 3D model where this panel must be placed. The total structure is build in this way. This is extremely fast since it is all dry assembly (no waiting times for concrete that has to cure for example). Everything is secured with specialized brackets and screw connections.
SPEED AND MANPOWER
On most jobs, the structure is assembled by only 4 people. 1 site manager and 3 workers. The site manager can operate the crane. The assembly team is assisted by the project manager that’s in charge for off site preparations. For example, a vacation-home is assembled in 2 days with a team of 4 people. That the structure is assembled very quickly is obvious. But the entire building process can also be accelerated by CLT. Because the openings of windows and doors are known perfectly in advance, they can be ordered and produced in advance. This allows them to come on site and be mounted simultaneously with the CLT structure. If the roof covering immediately follows the structure, it is possible to have a dry environment inside very quickly. Because the windows and doors are already attached to the structure, the facade finish is no longer on the critical path. It is therefore possible to continue finishing inside. The immediate availability of a dry environment indoors is a huge time optimization that one can never achieve with traditional materials.
Source: CLT-S Project KOCA, boardingschool
If LEAN plans are included in the process, speed gains are possible on all parts of the construction process.
Source: CLT-S Project Notary Office
An additional advantage, are the cut-outs for the utilities that have already been prepared. All transit openings are ready and no longer need to be cut or drilled on site. Installation of the utilities is therefore only a matter of mounting and screwing. A socket attachment must therefore only be screwed into the CLT with two screws. Not only is it much more efficient to assemble the utilities, it also reduces the chance of error.
ACOUSTIC AND FIRE
CLT is a lighter material. However, acoustics needs mass. That is why acoustics is a point of attention when using CLT as a structure. CLT-S manages to offer ‘increased acoustical comfort’ in residential buildings with its standard detailing. These solutions are all tested in situ and are therefore proven methods. The solutions are primarily based on decoupling walls with acoustic rubbers and decoupled brackets, as well as adding mass with a layer of gravel. Alternatively, it is also possible to work with additional walls or raised floors for office solutions.
Source: Detailing CLT-S
Acoustics are generally deserve more attention for CLT than for traditional construction, mainly because it is a new material with too few measured references. This will of course only benefit the final result.
In order to comply with fire reaction and fire resistance, the structure is dimensioned based on applicable standards and on based on the wall and floor structure used. Rf120 in high-rise buildings is possible, provided that the correct structures and additional materials are used. Fire reaction is usually addressed by treatment of the CLT or by adding drywall covering.
People sometimes have the wrong impression that wood is more flammable than other building materials. However, this is a faulty gut feeling that is not in accordance with the scientific knowledge that has been available for years.
EPB AND INSULATION
The inertia of a stone building is nowadays increasingly seen as a disadvantage. During winter, it has advantages because it absorbs heat and is more difficult to release, but in the summer this also applies. Once a traditional building has warmed up, it is very difficult to cool it down again. Wood is naturally less inert than stone. It therefore gives off its heat to the indoor environment more easily once it starts to cool down. During summer, this is a huge advantage because it allows the building to cool down very quickly at night, making it less likely to heat up during the day.
CLT is not only sustainable and circular, but the final building also meets current requirements in terms of energy consumption and sustainability.
CLT is a very attractive material to use for EPB and insulation values. Working with wood is, after all, working without thermal bridges. EPB moderate, CLT can be perfectly taken into account in the calculation.
FOUNDATIONS AND TOP-UPS
Given that CLT has about 1 / 4th of the weight of a traditional structure, it can provide solutions for situations where weight is a major cost driver or has structural limitations. Even with normal bearing soils, CLT can mean a saving in foundation costs. Based on the load reduction of the superstructure, the foundations and basement floors can be budgeted and optimized. For less load-bearing soil this means that it is possible to create more storeys than traditionally heavier structures or, for example, to avoid pile foundations.
CLT is therefore the ideal material for existing buildings to add a few layers. For example, CLT-S has already realized several congestion on the Belgian coast.
CIRCULAR AND ECOLOGICAL
CLT is produced with the FSC and PEFC label. In this way the origin of the wood can be traced reliably . The pine is sourced in the Austrian and Swedish forests where forest management has been a science in itself for centuries. The growth of the forests is always higher than the decrease, so the balance in the end is always positive.
Because trees capture so much CO2 during their lifetime and give oxygen in its place, wood as a building material is CO2 - negative, even calculated with production and transport emissions. This makes wood one of the most ecological materials to build with.
The CLT panels are also all dry mounted on site. As a result, they can also be dismantled and reused for other applications. All panels will soon also receive an RFID chip, so that the panels are not only identified during production and works, but also contain information that can be used for building management as well as for post-dismantling applications. This way it can be saved which type of panel has carried which loads and for which application it can be reused in the future.
There are 1 billion hectares of forests in Europe with an annual increase of 661,000 hectares. The standing timber stock in Europe is 22,500 million m3 of wood. Of these, there is an annual increase of 760 million. Today, only 1.5% of our stock is processed annually.