Ventilation strategies for crawl spaces in old churches

Many churches in Sweden are currently suffering from moisture and mold damage due to building construction, technical installations and changes in usage patterns. Churches with crawl space foundations often experience poor air quality caused by high humidity levels that promote microbial growth. Energy-saving measures such as reduced heating or complete shutdown during cold seasons can worsen these issues. Dehumidification using condensation or sorption dehumidifiers can be effective, but these methods are energy-intensive and therefore costly for the churches. The challenge lies in combining energy efficiency with the preservation of the building’s indoor environment and cultural heritage. The thesis aims to develop a more sustainable and economically justifiable strategy for preserving historic church buildings with crawl spaces. Through simulation and analysis of airflow, temperature variations and material properties, the goal is to identify ventilation solutions that ensure a stable and functional climate in the crawl space and thereby preventing moisture-related damage such as mold growth. The study includes both a literature review and a case study that includes site visits and simulations using the WUFI Plus software. Simulations are conducted with varied airflows conditions and with different building configurations and installations, for example with and without floor insulation and at different indoor temperatures in the church. The study shows that ventilation has a significant impact on moisture dynamics in crawl spaces and is strongly influenced by the outdoor climate. High air exchange rates lead to an increased intake of outdoor air. During late summer when humidity is high, the risk of mold growth is greatest, especially in unheated churches where indoor temperatures are low. The simulations show that the right balance between ventilation, insulation and indoor temperatures is crucial to avoiding moisture damage.