Identifying a Suitable Climate File for the Moisture Risk Assessment of Internally Insulated Walls Exposed to Solar-Driven Vapour Diffusion

In the UK, 20% of the building stock is subject to solar-driven vapour diffusion due to the un-rendered external surface of solid walls. Energy efficient interventions such as the installation of internal wall insulation can help to reduce greenhouse gases emissions and improve the thermal performance of those buildings. However, if the interventions are incorrectly designed, moisture accumulation may occur, which could be detrimental to the building and the health of its occupants. The moisture-related risk of such interventions is usually evaluated using hygrothermal simulations, however some of the input data required for the evaluation are not always suitable for the purpose; in particular, this is the case for external climate data.

The aim of this study is to identify a suitable climate file for the risk assessment of internally insulated walls affected by solar-driven vapour diffusion. This paper presents an evaluation of the commonly used typical and near-extreme reference climate files for moisture risk assessment. Hygrothermal simulations were carried out for both types of climate files and 19 years of measured data. Results indicate that the near-extreme files under-represent the worst-case scenario and that the penetration of rainwater does not significantly affect the output of the hygrothermal simulations. A distribution of climate files was found to be more accurate and representative for the moisture risk assessment when considering solar-driven vapour diffusion.