Assessing Different Insulation Strategies for Historic Wooden Facades Based on Modeled Mold Growth Risk

Abstract

Wood makes up a considerable proportion of applied construction materials in Chinese historic building envelopes. With increasing awareness of preserving historic heritage by promoting their further use and occupation, it becomes necessary to improve the current poor indoor thermal environment in abundantly existing historic buildings in southern China. One common approach for improvement is to install insulation materials on historic building envelopes, which can additionally improve their sustainability by reducing buildings’ energy demand for heating and cooling. However, this measure of deep retrofits requires cautious design regarding the hygrothermal performance of insulated wooden facades, since an improper construction way would lead to mold growth in wooden materials, causing problems of durability and indoor hygiene. Therefore, this study investigates the mold growth risk of different insulation systems for historic wooden facades in the Chinese HotSummer-Cold-Winter zone based on a parameter study. The considered parameters are internal and external insulation systems, vapor-open (mineral wool) and vapor-tight (XPS) insulation materials, a U-value of 0.8 W/(m²K) as well as a lower U-value of 0.24 W/(m²K) for the insulated walls, different capabilities and positions of an additional vapor control layer, as well as different cooling/dehumidification conditions in the warm period of a year. The hygrothermal performance of insulated wooden facades is simulated with WUFI®Plus software, while the mold growth risk is assessed with mold index values of the Viitanen mold model. The results of this paper will provide a quantitative evaluation of different insulation strategies for historic buildings in southern China regarding the mold growth risk in wooden materials, which is of essential importance for the durability of construction materials. This study can also give instructions for deeply retrofitting wooden historic buildings in China.

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