Hydrothermal monitoring using embedded sensors of the actual roof system of the Prado Museum

Abstract

El Prado Museum in Madrid has been recently submitted to a refurbishment of its roof which from been made with the traditional tiles has been changed to the use of modern waterproofing layers covered with a metallic lead finishing. Due to an unexpected damp patch that produced leaking in the hall in which Las Meninas by Velázquez was exhibited, the authors were commissioned by the Ministry of Education and Culture to study the suitability of the roof and its waterproofing properties. The study led to suggestions of modifications in the design of the roof layers, which are out of the scope of present paper. In present paper are given the behaviour of the sensors embedded in two specific areas of the roof. The sensors installed were of: temperature, relative humidity, measurement of local strain and detection of liquid water. The liquid water sensors reveal that some water is withheld in the layer just below the thermal insulation material, although it is standing. The results of over four years of readings show that the temperature attenuates over distance away from the outermost layer, where the readings are very high in summer, due to it consists of lead. During the colder seasons, in turn, the temperature in the inner layers of the roof is higher than in the outer layers. The strain recorded follows the logical evolution of temperature with no abnormal behaviour being detected. Some of relative humidity sensors had measuring problems due to water condensing on them. In summary however, if the behaviour in this area is extrapolated to the rest of the roof, it can be considered to perform correctly as intended. No more leaking events have been detected from the design modifications were incorporated to the existing roof.