Probabilistic Risk Assessment of Energy Efficient Retrofitting Techniques - Focus on Multi-family Dwellings and the Effects of Changing Air Movements

Licentiate thesis, 2012

Many of the residential buildings in Sweden have a large need of retrofitting; a result of insufficient maintenance and natural decay due to their predicted end of service life. These buildings must be taken into consideration in a near future where new and adapted technical solutions are required, suitable for the present conditions and the new demands of energy use. In Sweden, moisture safety is one of the concerns when designing for a retrofitting measure in residential buildings. Critical moisture levels in building materials increases the risk of developing mold and rot which can affect the performance of a building, durability and indoor environment, thus the human health. In terms of moisture safety, several concerns arise when choosing the most suitable technical solution for a retrofitting measure. One challenge is to find a solution with a low risk of future moisture related damages. In addition to knowledge and expertise, a technical solution for the retrofitting of the existing building envelope, may require a holistic view in order to understand and estimate the future performance of a building post-retrofit. The main purpose of the thesis is to identify and estimate possible consequences of changing air movements in residential buildings when performing different retrofitting measures. In a proactive manner, analyze new recommended retrofitting techniques in concerns of moisture safety and with the intention of providing a value of reliability. If the risks associated with different retrofitting measures are estimated, also the effect and potential economical impact on the Swedish building stock can be analyzed. The approach is to identify the number of buildings that can use the retrofitting technique; the probability that the technique will be used and the probability for severe moisture related damages post-retrofit. The final outcome is an indication of the potential costs for the stakeholders of the Swedish building stock, if a specific retrofitting technique is used. An existing risk analysis approach, a mode of procedure, has been improved and evaluated in a case study of a retrofitting technique. The model proved to be useful and yielded the expected value of risk as intended. Further the risk was implemented into statistical information on the Swedish building stock and the final result yielded a potential economical impact of the studied retrofitting measure if constructed. A risk assessment of the case study estimated that the investigated retrofitting technique could cost the stakeholders 360 million SEK on average. Consequently, a full scale probabilistic risk analysis in concerns of moisture safety is achievable, when predicting the future performance of retrofitting measures applied on Swedish residential buildings. Keywords: Retrofitting, risk assessment, hygrothermal, mold, costs