Evaluation of the thermohygrometric behavior of wooden roofing systems with under tile membranes to ensure durability

摘要

For several years innovative membranes that combine moisture barrier capability with relatively high vapor permeability have been available. However, data are lacking that quantify their performance for specific roofing systems and, in particular, those used for historic building in Italy. Therefore in the present study we have characterized the vapor transmission performance of several of these high permeability membranes and compared them with more traditional low permeability ones. The characterization was both experimental and numeric: timber roof and concrete roof test samples with different moisture barrier membranes were first submitted to steady climatic conditions on opposite sides in order to get severe conditions for moisture migration through the samples. The increase in moisture content of the samples over a period of four months was then used to calibrate a simulation model with the thermohygrometric parameters of the different test sample materials such that good agreement was obtained between the experimental and the calculated results. The simulation model was next used to estimate the behavior of the wood roof samples with the different membranes when exposed to one year climatic conditions of three Italian cities. The results show that for all the test samples moisture accumulation developed in the cold season and was eliminated in warm season, but in the case of a cold - humid climate (Venice), important differences - for health problems and materials durability - appeared in the moisture accumulation within the test samples with innovative high permeability or traditional membranes.