The hygrothermal properties of stone used in traditional construction: A Western European case study

Abstract

The importance of thermally upgrading the existing building stock to reduce environmental impact is widely recognised. It is imperative to ensure the adoption of correct approaches in upgrading traditional buildings, both to protect their unique character and to minimise potential decay in historic fabric. Hygrothermal modelling software, simulating the thermal and moisture behavior of walls before and after retrofitting, serves as a valuable tool for this purpose.

The full range of hygrothermal properties of low porosity building stones of Paleozoic origin, such as are typical in geological formations found in Ireland and Western Europe, have not been previously investigated. This knowledge is crucial for enhancing the accuracy of hygrothermal modelling of walls built of such stones. This research aims to bridge this knowledge gap by investigating material properties of a range of Irish stones, including bulk density, open porosity, sorption capacity, free saturation, vapour diffusion resistance factor, capillary absorption, drying and thermal conductivity.

Irish stones, particularly limestones, exhibit considerably higher densities than most reported by other international researchers and within the databases of the main hygrothermal simulation tools. The research identifies a trend of increased free saturation, vapour permeability, capillary absorption, and drying rates as the porosity of the stone increases. There is a substantial reduction in both vapour permeability and capillary absorption at low porosity levels (< 5 %), which help establish non-linear trend patterns for the correlation with these properties and porosity that are not generally seen in other research. The results show generally higher thermal conductivities at that porosity range. This is particularly important as many Irish building stones fall within this range, and existing datasets are therefore not applicable for these materials.

The utilization of this complete dataset of measured material data of Irish stone in this study in hygrothermal modelling is expected to significantly influence the thermal retrofitting approach for traditional solid stone walls.