Energy and moisture in historic masonry walls retrofitted with hemp-lime

Thermally insulating historic buildings is imperative in order to reduce energy demands of the existing building stock. Therefore an insulation material is needed that improves energy efficiency while being compatible with the existing structure from a hygrothermal, aesthetic and cultural heritage perspective. Hemp-lime is a building material that consists of on a combination of hemp shiv, the woody core part of the hemp stem, and building limes. The aim of this study was to determine if hemp-lime could be a feasible option for thermally insulating historic masonry walls in Sweden. The objectives were to measure energy performance of full-scale masonry façades insulated with hemp-lime and to monitor moisture levels inside the masonry walls. Three small single leaf masonry façades were constructed. One façade was uninsulated, the other had internal hemp-lime insulation and a third had external hemp-lime insulation. Energy use for space heating as well as temperature and relative humidity in the walls and rooms were monitored. Results show that thermally insulating historic masonry walls with hemp-lime can lead to an improvement in energy performance of 44-53 % compared to uninsulated single-leaf masonry. However, moisture levels were higher in the masonry façades that were insulated with hemp-lime.