An investigation into the vapour permeability and durability of natural renders on an earthen wall system
Abstract
This paper describes a novel methodology for establishing the relative moisture performance of renders used to protect a novel walling system combining traditional dense cob with a low-density thermal cob. A new method of enhancing the thermal insulation of cob walls has been developed by an European Union (EU)-funded joint UK and French project called CobBauge. The external surface of traditional cob walls (comprising subsoil, fibre and water) is normally protected from driving rain by placing the walls on a short wall called a plinth, a pronounced eaves overhang and a breathable exterior render. As the low-density fibre and clay insulating layer in the CobBauge system differs from traditional cob, a method of establishing the moisture-related performance of a range of renders needed to be instituted to aid the materials selection process. A series of test panels were constructed with the thermal cob infill, faced by a number of render types. The panels were hung in an open position in a high exposure zone and the moisture content monitored using wood-block sensors, electrical resistivity and gravimetric measurements over a period of six months. The wood-block and electrical resistivity moisture measurements showed a good level of agreement with gravimetric measurements and showed a clear differentiation between the various render choices.
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Author's Biography
Steve Goodhew researches sustainability and building performance of buildings both new and listed properties as individual units and also as urban groupings. He is an expert in the use of thermography and its use in relation to improving the building performance of homes and commercial properties. Prof Goodhew is a Fellow of the RICS, CIOB and RSA.
Matthew Fox is an architect, lecturer, and researcher in sustainable architecture at the University of Plymouth. Matthew’s research interests include earth construction, thermography, living wall systems and transient thermal investigation. He is the Architect of the CobBauge Building at the University of Plymouth
Jim Carfrae is a research fellow and lecturer at the University of Plymouth. Jim’s expertise is in the thermal and moisture performance of natural building materials particularly earth and straw-bale – His PhD thesis was on the moisture performance of straw-bale buildings.
Mohamed Boutouil is Deputy Director and Research Director at Builders. He is also a member of the CODIR Management Committee, CTI and HCERES accreditations. He is a specialist in innovative and sustainable construction materials. His specialities are management of research activities and development of research, academic and industrial partnership.
François Streiff is an architect, responsible for eco-materials and eco-construction at PnrMCB. He is Associate Professor for Science and Technology for Architecture at ENSA Normandie.
Kevin Owen is Senior Technician CobBauge Earth Building Interreg Research Project, DeVis Building Defect Visualisation via Thermography CREDS UK Research and Innovation.
Becky Little is an earth builder, using traditional techniques rooted in heritage and place. Her diverse projects focus on understanding the past and exploring identity through art, craft and building.
Karen Hood-Cree BSc (Hons) has successfully managed the award winning ‘CobBauge’ project for the past six years and is experienced in working and delivering multiple partner projects. She is an Alumni of the University of Plymouth (BSc (Hons), MSc).
Citation
Goodhew, Steve, Fox, Matthew, Carfrae, Jim, Boutouil, Mohamed, Streiff, François, Owen, Kevin, Little, Becky and Hood-Cree, Karen (2024, June 1). An investigation into the vapour permeability and durability of natural renders on an earthen wall system. In the Journal of Building Survey, Appraisal & Valuation, Volume 13, Issue 1. https://doi.org/10.69554/HWVB3187.
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