The effect of moisture on the thermal property of a reed thatch roof during the UK heating season

Simpson, A

Abstract

The hygrothermal performance of a replacement reed thatch roof with an insulation upgrade on Roadside cottage, a heated timber framed building in the UK, has been investigated over the winter months November 2020 to April 2021. The moisture content distribution in the roof has been determined empirically by moisture probe measurement three times a week. The in-situ measurements indicated the great importance of moisture in a reed thatched roof and the relationship with rainfall and sunshine levels. The rapid movement of moisture in and out of the outer layers of reed thatch demonstrated its excellent breathability.

The thermal conductivity of a specimen of reed thatch from the roof, as a function of moisture content, has also been measured in the laboratory. The results demonstrated the sensitivity of the thermal conductivity of thatch to moisture. Based on these steady state measurements for the existing reed thatch, the thermal performance during the heating season under complex environmental conditions has been evaluated. Uncertainties associated with thermal conductivity measurement and in-situ time variability of temperature are up to ±5%.

The mean moisture content and its subsequent effect on the thermal conductivity of reed thatch has been determined and a suggested average seasonal moisture content of 10% by wt derived. Under these conditions the U value of the 300 mm thick thatch, including insulation upgrade, meets modern insulation standards in the UK. Many thatch roofs are substantially thicker and it is possible that in some cases an insulation upgrade may not be necessary to meet the current UK requirements for replacement roofs insulated at rafter level.

Citation

Simpson, A. (2022). The effect of moisture on the thermal property of a reed thatch roof during the UK heating season. Energy and Buildings, 257(111777), 1-17. https://doi.org/10.1016/j.enbuild.2021.111777

• Journal Article Type: Article
• Acceptance Date: Dec 8, 2021
• Online Publication Date: Dec 11, 2021
• Publication Date: Feb 15, 2022
• Deposit Date: May 12, 2022
• Journal: Energy and Buildings
• Print ISSN: 0378-7788
• Publisher: Elsevier
• Volume: 257
• Issue: 111777
• Pages: 1-17
• DOI: https://doi.org/10.1016/j.enbuild.2021.111777
• Keywords: Reed thatch roof; Thermal conductivity; Moisture distribution; U Value; Weather conditions; Hygro-thermal performance
• Publisher URL: https://doi.org/10.1016/j.enbuild.2021.111777
• Related Public URLs: https://www.sciencedirect.com/journal/energy-and-buildings