Łukasz Bratasz, Dario Camuffo, Roman Kozłowski
A novel approach is proposed to establishing target indoor microclimates suitable for the preservation of organic materials susceptible to fracture and deformation, such as wood and paints. It assumes that it is impossible to establish a priori the best RH level for the conservation of mixed collections containing organic materials as over many decades they have adapted to a particular indoor environment within which they have been preserved. Therefore, the proposed strategy focuses on replicating the past average levels of RH and specifies bands of tolerable short-term fluctuations superimposed on these average levels. It is proposed to cut off 16 % of the largest, most risky fluctuations, which corresponds to one standard deviation in the distribution of the fluctuation amplitudes. Further, it is proposed to reduce the width of the target band of tolerable fluctuations by taking into account how much the fluctuations depart from the average seasonal RH level. The procedure is illustrated by three case studies of historic churches representative of different geographical locations, construction materials and patterns of use.