Luis Carli and Rafael Passarelli developed an interdisciplinary work between wooden architecture and information design through their research on wood dimensional changes. Known by many, especially in the field of architecture, construction, and design, most of the challenges of utilizing wood involve an understanding of wood-moisture relationships and its influence in wood properties. With this in mind, their work intends to provide a more comprehensive form for visualizing how different climate conditions influence different wood species regarding their dimensional stability. This also aims to provide a design tool for most wood-workers (from architects to cabinet-makers) that could quickly estimate the behavior of some wood species in a specific location along the year and, then, implement necessary design modifications in order to accommodate dimensional changes. More images and their description after the break.
Recently, due to the environmental issues, timber is being increasingly utilised in architecture, from structural purpose to cladding material. But, as many other natural materials, wood is hygroscopic, i.e. it exchanges moisture with its surrounding environment. As a piece of wood losses moisture it shrinks and as wood gains moisture back it swells. Dimensional changes due to moisture exchange in wood can lead to defects, such as warping, checking or splitting, that may compromise the performance of the wood piece or product.
Green wood refers to a condition in which the cell wall fibers are fully saturated with water and it starts about 30% MC for most wood species. This condition is usually seen in freshly sawn wood or wood that has been directly exposed to water. Any increase in MC over 30% will not affect wood dimensions. However, under the conditions in which wood is commonly used, its MC drops bellow 30%; as wood loses moisture bellow fiber saturation point it starts shrinking.
The amount of shrinkage will vary according to the wood species and, due to wood’s anisotropic behavior, direction. Basically, there are three main directions: perpendicular to the growth rings (radial direction), transverse to the growth rings (tangential direction) and parallel to the fiber orientation (axial or longitudinal direction). For longitudinal direction dimensional changes are very little, at most about 0.1%, they are left out.
After a certain time wood will reach a state of equilibrium with its surroundings. In this situation wood is neither gaining or losing moisture to the environment. Nevertheless, this equilibrium is dynamic: whenever the weather condition changes wood will try to reach achieve a different equilibrium MC value. As a given piece of wood loses moisture it shrinks and as wood gains moisture back it swells. For more detailed information on their data, please visit their website here.