IntroductionMulti-criteria assessment (MCA) is a methodology that supports making decisions by capturing multiple aspects. Building thermal insulation materials are products that have various properties including mechanical strength, fire resistance, acoustic performance, hygrothermal property and so on. In addition, Life Cycle Impact Assessment (LCIA) of the materials is gaining its importance with the growing interest on the design of sustainable buildings. However, there is limited number of studies which dealt with the selection of the material considering multiple aspects. This study applied MCA on common insulation materials (stone wool and expanded polystyrene (EPS)) to examine its effectiveness when selecting more environmentally friendly material.Experimental/Theoretical StudyAmong various MCA methods, the study applied analytical hierarchy process (AHP). AHP is one of the most common approaches for MCA that performs pair-wise comparison between different choices against each criterion. AHP integrates the compared results into single normalized scale as an output. Upon integration, weighting which reflects the relative importance of the criteria can be made. The study applied AHP for thermal insulation materials to be used for vertical walls by taking technical and environmental criteria: thermal conductivity (TC), compression strength (CS), fire resistance (FR) and global warming potential (GWP) via LCIA of the materials. Case studies were made in five scenarios with weighting of each of three criteria as top priority and no weighting which is shown in Table 1.CasesPrioritiesResultCase 1GWP > TC = CS = FRSW > EPSCase 2TC > CS = FR = GWPSW > EPSCase 3CS > FR = GWP = TCEPS > SWCase 4FR > GWP = TC = CSSW > EPSCase 5GWP = TC = CS = FRSW > EPSTable 1. Summary of priority of seven cases and their resultsResults and DiscussionFor Case 3 where compression strength was top priority, EPS was superior to Stone wool. With all the other cases, stone wool was preferable over EPS. Moreover, stone wool outperformed EPS even without weighting. This suggests that in contrary to conventional design practice, the inclusion of LCIA results in AHP encourages users to select more environmentally friendly material between the two for the investigated value criteria. As the weighting showed its importance upon selection of sustainable insulation materials, further investigation on the weighting scheme is necessary. ConclusionThe study applied MCA for assessing two typical building thermal insulation materials that took environmental and technical aspects into account. The result showed the effectiveness and challenge of using AHP for including LCIA results upon choosing sustainable insulation materials. Moreover, further consideration for compression strength is also necessary as it may require restrictions such as threshold value depending on specific building details, codes etc. In order to allow this MCA fully applicable for building design, further improvements on the method is necessary.Reference Huang, I.B., J. Keisler, and I. Linkov, Multi-criteria decision analysis in environmental sciences: ten years of applications and trends. Sci Total Environ, 409(19): p. 3578-94 (2011).