New technology in digital building, particularly Computer Numerical Control (CNC) systems, are changing the way that we design and build wooden structures. Their high level of precision allows us to design perfect assembles--without screws or visible metalwork--resulting in structures that are durable, easy-to-build, and extremely well-organized. We spoke with the experts at Timber to better understand the process of building a wooden structure and to compile a list of key tips in designing one.
.jpg?1554305368 "El Galeno Horse Stables and Warehouse / Peñafiel & Valdivieso Arquitectos. Image © Francisco Croxatto Viviani")
1. Choose wood types that can be easily mechanized and clearly define their sections.
To mechanize a wooden structure, you need to keep in mind the type of wood that you want to use and clearly distinguish its different sections. This will help prevent changes in the later stages of your project.
Surprisingly, many architects design their structures with sections that don't even exist--thanks to calculations done according to durability and rigidity requirements or because the wood chosen for the project cannot be mechanized, resulting in the need to change the entire system once everything is laid out. If you lack experience in these types of structures, it would be wise to consult with experts who can guide you through the process.
2. Study the different types of wood to understand their properties and how they change over time.
To give you an example, we will compare the properties of Monterrey Pine with Oregon Pine, taking a look at their laminated or hardwood forms.
Oregon Pine is highly resistant to humidity, termites, and mold, making it a recommendable choice for exterior structures. However, as hardwood, after being laid, Oregon Pine has the tendency to continuously shift, leading to damage and deformations that can prove difficult to fix. Monterrey Pine, on the other hand, is more stable and is a better choice for this type of use.
If it fits into your budget, we recommend that you choose laminated formats since they stay exactly the same from the time that they are installed, whether they're Oregon or Monterrey Pine. However, there are also a variety of natural finishes to choose from that give even more protection and durability to all types of wood, and that can last for up to 15 years.
3. Consider the location of your project and its tolerance to moisture swelling.
If you choose wood dried in a chamber, the degrees of humidity in the finished structures should remain stable, no matter the structure's location. However, if your project is on the coast, or in a humid environment, it's possible to modify the wood's tolerance, such as reducing its dimensions by a few millimeters to combat the swelling from contact with water.
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4. The larger a piece of wood is, the greater its resistance to fire.
In the case of structures, laminated wood is effectively resistant to fire, even more so than steel, as it's only its outer layers that burn.
For example, if an R30 fire resistance is needed (meaning that the structure will continue with its functions for at least 30 minutes) and the structure has a 42x150 mm piece of wood, you can add up to 1 minute of resistance by increasing the section by 0.7 millimeters. This means that, you should add 0.7 mm to get one minute of resistance. To go from R30 to R60, for example, you should increase the thickness of the wood by 2.1 cm.
5. The function and beauty of hidden joints
Along with traditional metal workings, there are a series of hidden joints and assemblies that can be attached with bolts or other metal pieces, connecting wood with wood or wood with other materials like concrete.
Cutting done by CNC results in a high level of precision, lowering the general costs of a project. Generally, the structure can be easily modeled by Cadwork software, compatible with Revit and other CNC machines.
Some of the most used combinations include:
Dovetail Joint
Made with a trapezoid-shaped cut, one of its extremes is always wider than the others.
Mortise and Tenon Joint
Achieved with a precise cut into one of the pieces, allowing the other piece to be tightly fitted connected with the other.
Hidden Metal Connectors
These connect wood with other materials like concrete.
6. Guiding design through clear regulations can reduce project costs
It is fundamental to always design with norms in mind. If norms appear incomplete or unclear, it's possible to look to more advanced norms set by other countries, ensuring the efficacy of your structure. For example, Eurocode 5, which covers all aspects of designing and building wooden structures, is a good guide for these types of projects.
When norms leave too much room for chance and speculation, engineers tend to increase the safety percentage by unnecessarily adding onto the structure.
Click on the image to see in detail the different pieces and joints presented in this article, used in Peumayen House by Aguilo + Pedraza Arquitectos:
