Preventive conservation of historic buildings in temperate climates. The importance of a risk-based analysis on the decision-making process

•Long-term monitoring of microclimatic parameters in a historic building.•Risk-based analysis to evaluate degradation phenomena.•Hygrothermal capacity of historic buildings to achieve microclimatic targets.•Real risks associated to natural indoor climates in temperate climate.•New classification to evaluate degradation risks and building response.

Historic buildings are usually characterized by a particular microclimate due to their high thermal inertia that may require the use of mechanical systems to control the environment. The guidelines used to define the indoor climate have evolved in recent years, with new methods and deepening the knowledge of the behaviour of materials, resulting in the publication of several risk-based methods.Despite the risk-based methods, the use of guidelines continue to play a leading role on the science of preventive conservation with the progressive assumption of less demanding targets. However these guidelines were usually defined for specific climates so that when extrapolated to other locations their application may not be positive.This research aims to analyze the hygrothermal behaviour of an unheated historic building in a temperate climate (Lisbon, Portugal) using a long-term monitoring and applying a risk-based analysis to the natural climate and to the climate limited by the historic set-point of 20 °C – 50% and the targets defined by the standards EN 15757 and PAS 198. Finally a classification was defined to assist in the decision-making processes and to verify if it is safe to impose less demanding targets in temperate climates, improving therefore energy economy.