Wood Weathering as Design Option

Abstract

The objective of the presented work is to provide a more thorough understanding of weathering colors and color patterns of untreated wooden claddings. The perspective taken throughout this work is that weathering is clearly an option for creating unique color settings on untreated wooden cladding and that a better knowledge of the color aspect of weathering will enable and encourage additional creative design in wood architecture. This approach is in direct contrast to the dominant view in the area of wood weathering research in which weathering is perceived as a negative consequence of weather exposure. Chapter 1 introduces the background of this study and specifies the research objectives. The current state of the research field is discussed in Chapter 2. Established methods in wood weathering research were of little relevance to this study. Hence, a preliminary idea-generating exercise on ways to approach the topic was made. Chapter 3, Section 3.1 discusses the preliminary exercise. The exercise resulted in four concepts for working with wood weathering: • Terms for describing weathering of untreated cladding • The Weathering Equation • Options for designing an untreated wooden cladding • Concepts on the relations between cladding design, weather exposure and weathering colors The investigation of color development of untreated wooden claddings is based on data obtained from experiments. The overall idea for the experimental design was to create a setup that simulated conditions as closely as possible to real life weathering of wooden cladding in order to generate data with maximum comparability and relevance to real life situations. The experimental setup was designed to simulate a house with four vertical, perpendicular façades. A series of 8 different claddings was designed using untreated, planed, quarter sawn heartwood of Scots Pine (Pinus Sylvestris L.). Each design was produced in four samples and placed in an above ground vertical position on walls facing approximately cardinal compass directions at Voll research fields in Trondheim, Norway. Each sample measured 60x900mm. After 20 months of exposure, the claddings were disassembled and the surfaces scanned with a flatbed scanner in the same manner as one would scan a piece of paper. Chapter 3, Sections 3.2 and 3.3 discuss details of the experimental design, setup and procedures.

The scanned images showed significant variations in the color development of identical samples that had been exposed to weather from four different directions. Since wind-driven rain and solar radiation are the main weather factors responsible for color changes on untreated wooden surfaces, a separate study was undertaken of the distribution of these weather elements at the Voll research fields. This study is used in Chapter 4 to help understand details of the color development of the claddings. Using data from an automatic weather station located at the Voll research fields, three types of weather maps were designed: • The Directional Weather Map. The map shows the main tendencies in the distribution of wind-driven rain, UV and sun hours on the horizon. • The Spherical Weather Map. The map was designed to give an overview of the mean annual distribution of rain and solar radiation on the hemisphere above Voll. • The Surface Weather map. The map was designed to visualize the distribution of wind-driven rain, UV and sun hours on the individual surfaces of the claddings in the experiment. The information provided by the weather maps was used to establish the suggestion of a relationship between the Voll weather and the weathering color development of the claddings. Chapter 3, Section 3.4 discusses the weather maps. Details in the modeling and calculation methods are found in Appendix C. The results documented that the four samples of each cladding type oriented towards four compass directions at the Voll research fields, developed differences in the weathering color and color patterns. The differences in color development could be explained by differences in weather incident on these four compass directions, as demonstrated by the weather maps. Chapter 4, Section 4.3-4.10 describes the weathering color development of the cladding and analyzes the relationship between cladding design, weather exposure and color development of the wood surfaces. The results also showed that current guidelines on weathering of untreated wooden cladding are inadequate for evaluating the potential weather exposure conditions and the subsequent color development of wooden cladding. A critical hypothesis of this work is that knowledge of the specific in-situ weather conditions is necessary when determining the color potentials of any given wooden cladding. The weather maps designed for this work provide information on the specific in-situ weather conditions. Chapter 5 discusses the results of this study in relation to current guidelines on weathering of untreated wooden cladding. The results obtained in this work point to a number of interesting options for further development of this field of research in ways that should appeal not just to the architectural profession but also to the general public, for whom the use of untreated wood and the ability to predict color outcomes in outdoor applications may be of interest. Chapter 6 discusses suggestions for future research.