The built environment usually constitutes a very important part of the real capital of a nation, and the construction sector represents more than 10% of the yearly Gross National Product of the industrialised world. Good planning of all construction is important, and consideration of the service life of the work is of great interest and is a significant aspect of sustainability considerations. The need for more knowledge about degradation of materials, for structured methodology, and for working tools for those involved in the planning process, has resulted in an extensive effort in pre-normative research and standardisation regarding this field.

This thesis presents a discussion on service life planning and the role of the Factor Method in such work, and especially, discussion of modification and development of the methodology. In the design process, the need to evaluate the service life of products is a great challenge, as the results will depend on both material properties and the environment in which the material is placed or used. A practical solution has to be based on a good knowledge in the field, but also on a sound working strategy, to ensure that different design scenarios can be compared in a standardised or structured way. The Factor Method is a promising working tool for such an evaluation and comparison, but is as such, still more of a methodology, than a method. Examples of the use of the methodology are still very limited, and the method as such, is much discussed by researchers. However, its future will depend upon how practical it will be to apply in use. The method is useful to estimate the service life of products, based on a known reference service life and a number of modifying factors. These factors in turn depend on the conditional differences between the specific project and the reference, in-use conditions. This thesis discusses the required precision of such a methodology, especially in light of inherent distributions in material properties, and the fact that the consequences of failure are often very limited. In such cases, the standardised Factor Method is considered to be quite useful, and should give the parties involved a good means for working in a structured and systematic way.