Development of a biologically active moss wall system as a sustainable exterior building envelope

Abstract

The integration of sustainable systems into the built environment is a critical response to the growing impacts of climate change, particularly in tropical regions. This research investigates the development and evaluation of a biologically active moss wall system as a sustainable exterior building envelope, with specific emphasis on structural feasibility, thermal performance, cost and environmental sustainability within the context of Sri Lanka’s tropical climate. A prototype moss wall system was designed using lightweight steel framing, moisture- retentive substrate layers, recirculating irrigation system and moss species adapted to local climatic conditions. Structural performance was analysed via analytical modelling and manual calculations to determine load-bearing capacity, wind resistance, and overall stability. Thermal performance was assessed through experimental monitoring by constructing four models using brick masonry, cement block masonry, plywood model with moss and double-layer configuration with moss. In addition, a computer simulation using DEROB-LTH, and as the results deviated from the actual measurements, a parametric study was carried out varying the factors relevant to solar radiation, thermal conductivity, specific heat, density, solar absorptance, and thermal emittance. Cost analysis was conducted for both conceptual and detailed designs, while sustainability evaluation was benchmarked against Sri Lanka Green Building Council (SLGBC, 2017) criteria. The actual measurement results indicated that moss-integrated walls particularly double-layer configurations, maintained lower indoor temperatures and higher relative humidity than masonry and cement block walls, indicating enhanced microclimatic stability and passive regulation of temperature and humidity. Although discrepancies were observed between measured results and DEROB-LTH simulations, parametric sensitivity analysis confirmed consistently improved thermal performance for moss walls. Structurally, the system meets design standards and allows flexibility in configuration, while the passive irrigation system maintains adequate moss hydration with minimal water consumption. Environmental benefits include improved air quality and potential mitigation of urban heat island effects. This study concludes that biologically active moss wall systems constitute a structurally viable, thermally efficient, and environmentally sustainable building envelope solution for tropical climates. The integration of such systems offers potential for reducing energy demand, enhancing occupant comfort, and contributing to urban sustainability. Further research is recommended to explore full-scale applications, design optimization, comprehensive lifecycle assessment and integration with smart building technologies.