Risk Assessment of Hygrothermal Performance - Building Envelope Retrofit

Doctoral thesis, 2013

A risk assessment of the hygrothermal performance for a building envelope retrofit investigates possible variations in energy performance, indoor environment quality and moisture safety and elaborates on the risks of exceeding defined acceptance criteria. These risks can be properly determined if including the variability of, by the investigated retrofit, most influencing parameters. As a result, the risks can also be presented with a variability, which subsequently can serve as a realistic and credible basis of judgment for risk tolerability decisions. In general today, the risks of exceeding defined performance criteria are assessed based on the results of a deterministic hygrothermal calculation tool; an evaluation, in which the influencing parameters, such as material properties, indoor and outdoor climates are provided with fixed values. The result of such deterministic analysis will represent a single best-estimate of the future hygrothermal performance of the building. Consequently, the performance of the retrofitting measure, as a result of a deterministic simulation, will likely be underestimated or overestimated, since such analysis provides no expected variation of the hygrothermal performance. Actually, the result of a deterministic analysis represents an average hygrothermal performance; it takes no consideration, what so ever, to the expected deviations from that specific performance or the probability of occurrence. However, the proposed risk assessment of a retrofitting measure will include the variability of the influencing parameters; thus, generating results which provides an expected deviation from the best-estimate and proper decisions can be made on the risks of exceeding acceptable performance levels. In addition, a risk assessment includes result, sensitivity and uncertainty analyses which enable an appropriate and credible evaluation of the retrofit, help to better understand the performance of the retrofit design and enable improvements of the design, if needed. This thesis thoroughly describes a hygrothermal risk assessment procedure, including both a qualitative and quantitative risk analysis, and provides concrete examples of practice through several case studies.