Building Envelope Performance Assessments in Harsh Climates: Methods for Geographically Dependent Design

Abstract

The lifetime of the built environment depends strongly on the severity of local climatic conditions. A well-functioning and reliable infrastructure is a precondition for economic growth and social development. The climate and topography of Norway puts great demands on the design and localization of buildings. The relationship between materials, structures and climatic impact is highly complex; illustrating the need for new and improved methods for vulnerability assessment of building envelope performance in relation to externally imposed climatic strains. Historically, major variations in climatic impact have led to corresponding large variations in building practice throughout the country - often well suited to local conditions. Today it is fair to say that sound building traditions and practice to some extent are being rejected in the quest for cost-effective solutions. Furthermore, projected changes in climatic conditions due to global warming will enhance the vulnerability within the built environment.

The primary objectives of the present dissertation are to increase the knowledge about possible impacts of climate change on building envelope performance, and to analyse and update methods for the planning and design of external envelopes in relation to climatic impact. This is accomplished through the development of integrated approaches and improved methods for assessing impacts of external climatic parameters on building envelopes, combining knowledge on materials, structures and relevant climate data, applicable for both historical data and scenarios for climate change. The results will contribute to more accurate building physics design guidelines, promoting high-performance building envelopes in harsh climates.

Approaches to assessments of the risks associated with climate change and buildings are suggested, identifying main areas of vulnerability in the construction industry. It is shown that there are benefits to be gained from the introduction of risk management strategies within a greater extent of the construction industry. A way of analysing the building economics of climate change is also proposed

Analyses of building defects are necessary in order to further develop tools, solutions and preventive measures ensuring high-performance building envelopes. To illuminate the vulnerability of different building envelope elements under varying climatic exposure, a comprehensive analysis of empirical data gathered from process induced building defect assignments is carried out. The amount of building defects in Norway clearly illustrates that it is not only the extreme weather events that need to be studied as a foundation for adaptation towards a changing climate. Furthermore, the analyses of defects reveal a fundamental need for climate differentiated design guidelines.

New and improved methods for geographically dependent design of building envelopes are proposed:

- A method for assessing the relative potential of frost decay or frost damage of porous, mineral building materials exposed to a given climate is developed.

- A national map of the potential for decay in wood structures is developed. Detailed scenarios for climate change for selected locations in Norway are used to provide an indication of the possible future development of decay rates.

- A method for assessing driving rain exposures based on multi-year records of synoptic observations of present weather, wind speed and direction is also presented.

These climate indices can be used as a tool for evaluation of changes in performance requirements or decay rates due to climate change under global warming incorporating data from regional- and local-level climate change scenarios. Historical records of climate data have finally been used to illuminate challenges arising when introducing international standards at the national level, without considering the need for adjustments to reflect varying local climatic conditions.

At present, building standards and design guidelines presuppose use of historic weather data. Historically, location-specific climate data have only to a very limited extent been applied systematically for design purposes, life cycle assessments, and climate differentiation of the suitability of a given technical solution in a given climate. The work is a first step towards methods and approaches allowing for geographically dependent climate considerations to be made in the development of design guidelines for high-performance building envelopes, and also approaches to assess the risks associated with the future performance of building envelopes due to climate change.

The dissertation focuses on methods for assessing impacts of external climatic parameters on a local scale, but with the use of daily and monthly averages of climate data. The reliability of climate indices or climate differentiated design guidelines is strongly dependent on the geographical spreading of the observing station network. The Norwegian network is not optimally distributed to fully embrace local variations, but provides a solid platform for the development of methods for geographically dependent design and guidelines on the appropriateness of different solutions in different climates.

Climate indices (using geographic information systems technology)allowing for quantitative assessment of building envelope performance or decay potential may be an important element in the development of adaptation measures to meet the future risks of climate change in different parts of the world. Finally, the work offers a conceptual point of departure for the development of a vintage model of the robustness of the Norwegian building stock.