The dissertation consist of five parts:The purpose of the first part is to give the reader an introduction to the subjects of deterioration mechanisms, loss of function for building envelope components and prediction of service life for building envelope components.The purpose of the second part is to describe, compare and criticise the standards, guides and methods dealing with service life prediction which are currently available. The standards are not the only available information regarding service life prediction, as a number of researchers have developed methods which are based on either a structural engineering approach, a probabilistic approach or methods that are further developments of the deterministic approaches which the national and international standards are based on. Although the relation between the structural engineering and service life prediction has been recognised, none of the described structural engineering approaches reveal a potential for further development.Two probabilistic approaches are described, one approach using a mathematical function (Weibull) to describe the performance of a component over time and one approach using discrete Markov chains.Finally, two variations of the method specified in the Japanese guide and a later ISO standard have been described and examined. Instead of using modifying factors, the two variations introduce statistical functions to describe the influence of the indoor/outdoor climate, quality of materials/work etc., and as such combine the deterministic and probabilistic approach. Based on an investigation of the data-requirement, user-friendliness and supposed accuracy (the accuracy of the different methods has not been evaluated due to the absence of field data) the method which combines the deterministic factor method with statistical distributions for the factors is recommended as the preferred method. The third part of the dissertation consists of the next two chapters. The aim of the first one is to describe how durability assessment can be included in the design process and in the following chapter a holistic design process for the building envelope is described which takes into account all relevant aspects, e.g. thermal performance, cost, durability, aesthetics etc.In the fourth part, the method, which was developed in the previous chapters, is illustrated by evaluating two innovative building envelope components that were designed to be prepared for repair and maintenance. Both of these components are insulation systems for flat roofs and low slope roofs; components where repair or replacement is very expensive if the roofing material fails in its function. The principle of both roofing insulation systems is that the insulation can be dried, a task which is impossible in traditional flat roof insulation systems. The drying is made possible by ventilation with outside air through or below the insulation layer for a short period of time once water has been detected. The properties and performance of the systems have been evaluated by experiments in the laboratory and by using a proposed method. Both roofing insulation systems showed good performance in the experiments and in the performance assessment.The final section of the dissertation consists of the the conclusions of the dissertation and the recommendations for further work are given. The conclusions are divided into three smaller parts regarding the description of the current methods, description of a developed method and use of the findings to evaluate the performance of two innovative building envelope components.The recommendations for further work points at a number of issues which are specified below:Further development of methods for designing building envelope components prepared for repair and maintenance, and ways of tracking and predicting performance through time once the components have been designed, implemented in a building design and built.Development of a uniform description format for building envelope components where a designer can easily compare certain or all relevant aspects of building envelope components during the design process. This is in contrast to the current situation where some of the information may be available but organised in a different way for each component.Further development of building envelope components that through their design are prepared for repair and maintenance so that expensive repair and replacement may be avoided. Examples of components in need of such a design process could be internal insulation systems where condensation can be removed if detected (including an easy method for detection of moisture) and wall systems where extra insulation can easily be inserted later on if demanded.