Investigating the performance of hempcrete as an option for retrofitting masonry buildings

Abstract

One fifth of the energy consumed by buildings in Sweden is by those built before 1945, many of them constructed from solid masonry walls. Improving their heating energy consumption is a challenge we must face in light of human’s impact on climate change as well as increasing energy costs. Improving thermal performance can be achieved with many insulating materials however the environmental impact of the materials themselves must also be considered as does the hygrothermal effect on the existing building structure. Hempcrete has been accredited with both environmental and hygrothermal benefits in both retrofitting and new build projects but as a relatively new material its properties are not entirely understood, consequently steady state calculations and simulations of heating energy use are proving to underestimate measured performance. The aim of this study was to evaluate the viability of hempcrete as an insulation material when retrofitting solid masonry walls to low energy standards with regards to moisture safety using industry standard software to simulate the results and a mathematical model to assess the mould risk. The Life Cycle Cost and Analysis was also calculated. Results show that hempcrete would be viable and perform very well environmentally for this application but there are questions over the predicted hygrothermal performance and consequently moisture safety due to the complexity of modelling the dynamic behaviour of hempcrete as it has shown in physical tests to perform better than expected.

Popular Abstract

An evaluation of the viability of hempcrete as an insulation material when retrofitting solid masonry walls to low energy standards.

Introduction
When improving the thermal performance of existing masonry buildings the environmental impact of the materials themselves and the hygrothermal effect on the existing building structure must be considered. This report highlights the importance of considering the methods employed in predicting heating energy use and moisture safety when it comes to hempcrete.

Main text
Hempcrete is shown here to perform very well environmentally and when considering the hygrothermal benefits in retrofitting solid masonry walls although as a relatively new material its properties are not entirely understood, consequently steady state calculations and simulations of heating energy use are proving to underestimate measured performance.

One fifth of the energy consumed by buildings in Sweden is by those built before 1945, many of them constructed from solid masonry walls. Improving their heating energy consumption is a challenge we must face in light of human’s impact on climate change as well as increasing energy costs. Improving thermal performance can be achieved with many insulating materials however the environmental impact of the materials themselves must also be considered as does the hygrothermal effect on the existing building structure. Hempcrete, sometimes referred to as hemp-lime or lime-hemp-concrete has been accredited with both environmental and hygrothermal benefits in retrofitting and new build projects but as a relatively new material its properties are not entirely understood, consequently steady state calculations and simulations of heating energy use are proving to underestimate measured performance. In this study space heating energy simulations overestimate actual consumption by approximately 28% compared to the same simulation using cavity brick walls and mineral wool which over estimated by just 6%. The discrepancy may be attributed to the complex hygrothermal conditions evident in hempcrete which influences its thermal conductivity and specific heat capacity. Heat cannot be considered separately from moisture, the processes of water adsorbtion, desorbtion, vapourisation and condensation within the wall assembly have been shown to greatly effect thermal performance. These are of particular importance in a hygroscopic material such as hempcrete although paradoxically not normally considered as dynamic properties in energy simulations. Ignoring these phenomena result is the undervaluing of hempcrete when comparing it to other insulating options but its energy saving qualities are not the only benefit when retrofitting masonry walls. Comparing internally insulated walls using hempcrete or mineral wool shows that moisture entering the wall from outside does not dry out when using mineral wool but accumulates at the inner masonry face while hempcrete allows moisture to transport via capillary action or diffusion through the entire wall in a way similar to that of masonry only. Mould analysis of the insulation indicates no risk in either construction even when tested against climate data predicted for the end of the 21st century however, the reliability of these models has been questioned by others with an underestimation of mould probability shown. This study indicates the risk is not mould but moisture levels in the existing wall and that it may be more prudent to consider the known moisture transport characteristics of retrofit options when considering moisture safety. Hempcrete is shown to function sympathetically with the hygrothermal conditions of the existing masonry walls and can be considered a safe option for the case in this report.
The environmental impact assessed through Life Cycle Analysis indicates that hempcrete performs less well than glass mineral wool in four of the seven chosen categories due to agricultural processes however, the Ozone Depletion Potential is zero and the Global Warming Potential as a result of CO2 sequestration is negative making hempcrete a good choice if a building’s impact on global warming is to be considered.
Life Cycle Cost was also calculated. This is effected by the accuracy of predicted heating energy use which, if undervalued as it is in this case performs less well than glass mineral wool over a 50 year life time. However if it is assumed that energy use will be better than predicted hempcrete may very well perform better economically than mineral wool.

• author: Lanham, Henry
• supervisor: Vahid Nik
• organization: Department of Architecture and Built Environment; Division of Energy and Building Design
• course: AEBM01 20191
• year: 2019
• type: H2 - Master's Degree (Two Years)
• subject: Technology and Engineering
• keywords: Hempcrete, lime-hemp Miljöbyggnad, moisture safety, future climate, energy use, mould risk.
• language: English
• id: 8988359
• date added to LUP: 2019-06-26 14:43:44
• date last changed: 2019-06-26 14:43:44