Monitoring of a Cold Roof Thatched with Reed (Phragmites australis) Using Wooden Substitute Sensors for Moisture Content Measurements

Abstract Reed (Phragmites australis (Cav.) Trin. ex Steud.) is a traditional building material in many parts of the world and provides service lives of more than 50 years when used for thatching. However, during the last decades a significant number of thatched roofs showed premature failure due to decay. Potential reasons for this are manifold but not clearly identified, yet. This monitoring project aimed therefore on investigating the moisture and temperature conditions within a thatched roof structure showing severe degradation after only seven years in service to obtain more information about the decay risk of reed and its potential causes. Highest moisture loads were found on the outermost layers of the North-faced roof, which also showed superficial growth of algae, lichens, and mosses. However, it stayed unclear if increased moisture content (MC) was the reason for or the consequence of decay. An increased MC was also found where the roof pitch turned from steep to flat. The use of so-called substitute sensors made from preservative treated wood turned out as a useful method to determine equilibrium moisture contents as well as time of wetness in reed structures and might be applied also for further field testing and monitoring with reed, straw, or other organic fibrous materials.