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The greatest challenges facing straw bale building in Japan, and many other countries with high humidity and precipitation, are moisture and the susceptibility of straw to microbial decay. Researchers in Europe and North America have found the use of ventilated rainscreens to help control interstitial moisture in straw bale walls. The indoor, outdoor and interstitial hygrothermal environment of six straw bale structures in Japan have been monitored. The six buildings are organized into two groups. The first group includes buildings consisting of straw bales walls with an earthen or lime plastered exterior finish applied directly to the bale walls. The second group includes buildings consisting of straw bale walls utilizing ventilated rain screens. The purpose of the present study is: (one) evaluate the potential for mold growth in the six buildings, (two) clarify moisture dynamics, and (three) determine the effectiveness of ventilated rainscreens to control moisture in straw bale walls. As a result of the study, the potential for mold growth was found to vary by structure. Buildings utilizing rain screens were found to have lower interstitial relative humidity and a lower risk of mold growth. Keywords: straw bale building; ventilated rainscreens; hygrothermal environment; mold growth; interstitial moisture 1. Introduction precipitation, are moisture and the susceptibility of Straw bales are blocks of compressed straw. In straw straw to microbial decay. bale construction, bales are stacked to create bearing or However, controlling moisture to reduce microbial infill walls. decay and improve building durability is an issue Straw bale building has numerous ecological common to conventional construction and particularly advantages. Straw bales are low in embodied energy buildings utilizing organic insulations such as straw, (Centre for Building Performance Research, 2010). rice hulls, etc. (Lee et al., 2013). Since straw consists of approximately 36% carbon, Straw bale walls are generally finished with earthen straw bale walls function as a carbon sink, sequestering and/or lime plasters applied directly to the bale walls. carbon during the life of the building (Wihan, 2007). In recent years, ventilated rainscreens have been Straw bale walls are also highly insulative, reducing employed to protect straw bale walls from moisture energy use and CO2 emissions due to heating and damage. cooling (Bigland-Pritchard, 2005). And lastly, upon The term "rainscreen" refers to the use of a drainage deconstruction, straw bales can safely decompose plane/air gap between exterior siding and bale wall. without becoming landfill. Permeable plasters tend to be porous and absorb Straw bale building is relatively new to Japan. exterior moisture. In many cases, this moisture is then According to the Japan Straw Bale House Association transferred to interstitial bales through capillary action. (2009), the first straw bale home in Japan was In order to prevent liquid water, i.e. rain, from direct completed in 2001 in Tochigi Prefecture. The greatest contact with a plastered bale wall, rain-screens can be challenges facing straw bale buildings in Japan, used. Previous research has found that rainscreens help and many other countries with high humidity and control interstitial moisture in straw bale walls (Carfrae et al., 2009; Lawrence et al., 2009; Otto et al., 2008; Thompson, 2006). *Contact Author: Kyle Holzhueter, Research Associate, The indoor, outdoor and interstitial hygrothermal Graduate School of Bioresource Sciences, Nihon University, environment of six straw bale structures in Japan have 1866 Kameino Fujisawa Kanagawa, 252-8510, Japan been monitored. These six straw bale buildings are Tel: +81-466-84-3364 Fax: +81-466-84-4464 organized into two groups according to construction E-mail: email@example.com details (Fig.1., Table 1.). The first Group A includes ( Received April 7, 2014 ; accepted November 12, 2014 ) Journal of Asian Architecture and Building Engineering/January 2015/212 205 buildings consisting of straw bale walls with an earthen 2. Materials and Methods or lime plastered exterior finish applied directly to the 2.1 Monitoring the Hygrothermal Environment bale walls. The second Group B includes buildings T and D Corporation's Thermo Recorder consisting of straw bale walls utilizing ventilated rain sensors monitor the indoor, outdoor and interstitial screens. hygrothermal conditions of the six straw bale The purpose of the present study is to (one) evaluate structures (Fig.2.). These sensors measure temperature the potential for mold growth in the six buildings, and relative humidity, and data is recorded at one hour (two) clarify moisture dynamics, and (three) determine intervals by data loggers. the effectiveness of ventilated rainscreens to control In Group A buildings, a "stack" of nine interstitial moisture in straw bale walls. sensors have been installed at various heights and Group A Group B Shinrinbokujo Tango Kyoto Leyenda Madenaie Toyama Fukushima Yurikagonoie Mie Earthen or Lime Plaster Ventilated Finish Rainscreen Furyu Outside Inside Chiba Outside Inside Square One Hokkaido Fig.1. Six Straw Bale Buildings Divided into Two Groups Table 1. Details of Each Building One Year Construction Principle Builder of Observation Period Group Building Name Prefecture City Architect Straw Bale Walls Start Finish Start Finish Shinrinnobokujo Kyoto Kyotango Goichi Oiwa Takao Kobayashi Oct-07 Jun-08 Sep-08 Aug-09 Tango Furyu Chiba Minamiboso Goichi Oiwa Takao Kobayashi Mar-08 Nov-08 Feb-09 Jan-10 Masatoshi Yurikagonoie Mie Tsu Hideto Oshima Feb-09 Jul-09 Jul-10 Jun-11 Sakamoto Mikio and Square One Hokkaido Asahikawa Stefan Bell May-09 Jun-10 Nov-11 Oct-12 Masami Sakai Yoshiyuki Kyle Holzhueter, Madenaie Fukushima Itate Nov-09 Mar-10 Dec-11 Nov-12 Toyoto Koji Itonaga Shoko Hiroaki Yoshimoto, Leyenda Toyama Toyama Aug-10 Sep-11 Apr-12 Mar-13 Yoshimoto Kyle Holzhueter 206 JAABE vol.14 no.1 January 2015 Kyle Holzhueter Group A Shinrinbokujo Tango, Kyoto Yurikagonoie, Mie Furyu, Chiba Square One, Hokkaido Group B HE HI ME MI LI LE Madenaie, Fukushima Leyenda, Toyama Fig.2. Wall Section and Sensor Locations for Each Building JAABE vol.14 no.1 January 2015 Kyle Holzhueter 207 depths perpendicular to the plane of the wall in each installed. Previous research by Holzhueter and Itonaga building (Fig.3.). Each interstitial sensor is given a (2010, 2014) and the results of the present study name consisting of multiple letters. The first letter suggest that a thorough investigation of the interstitial designates the height: "L" stands for low, "M" for hygrothermal environment is possible with the sensor middle, and "H" for high. The second letter describes arrangement of Group B. the sensors depth: "I" stands for interior, "N" for Collecting data over several years from multiple interstitial and "E" for exterior. buildings has resulted in the loss of some data. In Group B buildings, a "stack" of six interstitial However, despite the absence of some data, an accurate sensors have been installed at various heights and and thorough investigation is attainable. depths perpendicular to the plane of the wall. The No data is available from Furyu's indoor sensor nomenclature of the sensors follows Group A. Due between 17:00 September, 15, 2009 and 23:00 January to funding limitations, interstitial sensors were not 31, 2010. Group A Group B Fig.3. Stack of Nine Interstitial Sensors in Group A Buildings and Stack of Six Interstitial Sensors in Group B Buildings Table 2. Monitoring Results Summary of Six Buildings Difference Outdoor between Maximum Interstitial Maximum Total Total Interstitial Hours Surpassing 80% Relative Humidity Total Monthly One Year Indoor Outdoor Monthly Mean and 10℃ Guideline Outdoor and Mean Relative Humidity Group Building Observation Hours Hours Relative Greatest Period Surpassing Surpassing Total Humidity Guideline Guideline Total Max Consecutive Interstitial (％) Date Location (％) Date Hours Location Total Hours Location Hours Date LI 1705 HE 303 MI 169 Shinrinnobokujo 2008/09-2009/08 HN 50 LI 1369 2009/7/5-8/31 275 2849 1144 86 Aug-09 LI 87 Nov-08 Tango HI 34 ME 33 LN 15 LN 2849 LE 2730 LI 2682 HN 1512 Furyu 2009/02-2010/01 HE 1387 LN 1865 2009/6/2-8/19 661 3700 851 92 Jul-09 LN, LE 92 Jul-09 ME 1227 MN 1165 MI 1093 HI 961 LI 105 Yurikagonoie 2010/07-2011/06 LI 75 2010/07/18-21 8 1711 1606 76 Aug-10 LI 73 Aug-10 LE 6 ME 4177 2012/05/28- Square One 2011/11-2012/10 ME 3183 0 1990 -2187 95 Feb-12 HE 93 Jan-12 HE 1158 10/08 Madeinaie 2011/12-2012/11 na 0 na 0 na 0 2875 2875 76 Aug-12 LE 89 Sep-12 Leyenda 2012/04-2013/03 LE 4 LE 4 13/3/7 29 2485 2481 75 Jan-13 LE 84 Dec-12 208 JAABE vol.14 no.1 January 2015 Kyle Holzhueter GROUP A LI ﾟC LI %RH Guideline ﾟC Guideline %RH HE ﾟC HE %RH Guideline ﾟC Guideline %RH 90 90 80 80 70 70 -10 Shinrinnobokujo Tango, Kyoto Furyu, Chiba LI ﾟC LI %RH Guideline ﾟC Guideline %RH LE ﾟC LE %RH Guideline ﾟC Guideline %RH 90 90 80 80 70 70 -10 Yurikagonoie, Mie Square One, Hokkaido GROUP B Leyenda, Toyama Madeinoie, Fukushima Fig.4. Evaluation of Mold Growth Given an 80% Relative Humidity and 10ºC Temperature Guideline JAABE vol.14 no.1 January 2015 Kyle Holzhueter 209 2008/09/01 2010/07/01 2008/09/14 2010/07/14 2008/09/29 2010/07/27 2010/08/09 2008/10/13 2010/08/22 2008/10/26 2010/09/05 2008/11/09 2010/09/18 2008/11/23 2010/10/01 2008/12/07 2010/10/14 2008/12/21 2010/10/27 2009/01/04 2010/11/10 2009/01/18 2010/11/23 2009/02/01 2010/12/06 2009/02/15 2010/12/19 2009/03/01 2011/01/01 2009/03/15 2011/01/15 2009/03/29 2011/01/28 2009/04/12 2011/02/10 2009/04/26 2011/02/23 2011/03/09 2009/05/10 2011/03/22 2009/05/24 2011/04/04 2009/06/07 2011/04/17 2009/06/21 2011/04/30 2009/07/05 2011/05/14 2009/07/19 2011/05/27 2009/08/02 2011/06/09 2009/08/16 2011/06/22 2009/08/30 2010/07/01 2008/09/01 2010/07/14 2008/09/15 2010/07/27 2008/09/29 2010/08/09 2008/10/13 2010/08/22 2008/10/27 2010/09/05 2008/11/10 2010/09/18 2008/11/25 2010/10/01 2008/12/09 2010/10/14 2008/12/23 2010/10/27 2009/01/06 2010/11/10 2009/01/20 2010/11/23 2009/02/03 2010/12/06 2009/02/18 2010/12/19 2011/01/01 2009/03/04 2011/01/15 2009/03/18 2011/01/28 2009/04/01 2011/02/10 2009/04/15 2011/02/23 2009/04/29 2011/03/09 2009/05/14 2011/03/22 2009/05/28 2011/04/04 2009/06/11 2011/04/17 2009/06/25 2011/04/30 2009/07/09 2011/05/14 2009/07/24 2011/05/27 2009/08/07 2011/06/09 2009/08/21 2011/06/22 No data is available from Square One's HI, HN and 10ºC are understood to be a safe guideline for straw bale HE sensors between 11:00, October 8, 2012 and 23:00, walls. Above 80% relative humidity and 10ºC, mold October 31, 2012. Data is also not available from growth is predicted. At and below 80% relative humidity Square One's Outdoor sensor between 0:00, November and 10ºC, some biological activity may be present, but 1, 2011 and 17:00, November 9, 2011. is not believed to impact the life of the building. No data is available from Leyenda's Outdoor sensor The straw bale walls of the six buildings are between 19:00 November 13, 2012 and 0:00 December evaluated given this guideline. 6, 2012. 2.3 Clarifying Moisture Dynamics No data is available from Madeinaie's MI sensor The sensor locations which surpass the guideline are between 15:00 February 27, 2012 and 23:00 further investigated to clarify moisture dynamics. November, 30, 2012. Simultaneously depicting the relative humidity 2.2 Predicting Mold Growth readings of multiple sensors recorded at one-hour First, in order to evaluate the potential for mold intervals over an entire year on the same graph results growth in straw bale walls, the interstitial hygrothermal in incomprehensible figures. In order to visually depict environment is evaluated given a relative humidity and the moisture dynamics over an entire year in an easily temperature guideline. Holzhueter (2011) found that understandable manner, monthly averages are graphed. hygrothermal conditions of 80% relative humidity and Trends in relative humidity will be identified. GROUP A LI LN Indoor Outdoor LI HE Indoor Outdoor 100 100 90 90 80 80 70 70 60 60 50 50 Sep- Oct- Nov- Dec- Jan- Feb- Mar- Apr- May- Jun- Jul- Aug- Feb- Mar- Apr- May- Jun- Jul- Aug- Sep- Oct- Nov- Dec- Jan- 08 08 08 08 09 09 09 09 09 09 09 09 09 09 09 09 09 09 09 09 09 09 09 10 Shinrinnobokujo Tango, Kyoto Furyu, Chiba LI LE Indoor Outdoor ME HE Indoor Outdoor 70 80 10 10 0 0 Jul-10 Aug- Sep- Oct- Nov- Dec- Jan- Feb- Mar- Apr- May- Jun- Nov- Dec- Jan- Feb- Mar- Apr- May- Jun- Jul- Aug- Sep- Oct- 10 10 10 10 10 11 11 11 11 11 11 11 11 12 12 12 12 12 12 12 12 12 12 Yurikagonoie, Mie Square One, Hokkaido GROUP B LE Indoor Outdoor LE Indoor Outdoor 100 100 90 90 80 80 70 70 60 60 50 50 Apr- May- Jun- Jul- Aug- Sep- Oct- Nov- Dec- Jan- Feb- Mar- Dec- Jan- Feb- Mar- Apr- May- Jun- Jul- Aug- Sep- Oct- Nov- 12 12 12 12 12 12 12 12 12 13 13 13 11 12 12 12 12 12 12 12 12 12 12 12 Leyenda, Toyama Madeinoie, Fukushima Fig.5. Mean Monthly Relative Humidity of Indoor, Outdoor and Interstitial Sensors with the Highest Monthly Mean Relative Humidity 210 JAABE vol.14 no.1 January 2015 Kyle Holzhueter Relative Humidity (%) Relative Humidity (%) Relative Humidity (%) Relative Humidity (%) Relative Humidity (%) Relative Humidity (%) 2.4 Determining the Effectiveness of Ventilated none of the Group B buildings' interstitial monthly Rainscreens to Reduce Interstitial Moisture mean relative humidity surpass the outdoor monthly Through an evaluation of the potential for mold mean relative humidity. growth and a clarification of moisture dynamics, the All of Furyu's sensors surpassed the guideline by influence of rainscreens on interstitial moisture can be hundreds of hours. However, Furyu also had the most examined. severe climate. Furthermore, it must be remembered that the six When comparing the difference between interstitial buildings monitored are located in unique locations and outdoor hours surpassing the guideline, Square and climates. In order to compare buildings in different One performed the worst. However, despite having the locations and climates, the interstitial hygrothermal sensor with the highest number of hours surpass the environment is evaluated given its specific climate. guideline, only two of Square One's nine interstitial The sensor which surpasses the guideline by the sensors surpassed the guideline. This suggests a greatest number of hours is compared to the ambient localized problem near the exterior finish. environment. For example, the number of hours the Many of Shinrinnobokujo Tango's sensors surpassed interstitial sensor surpasses the guideline is subtracted the guideline. Shinrinnobokujo Tango also had a severe from the number of hours the outdoor sensor surpasses climate, but the climate was similar to Group B's the guideline. A building with a positive value has Madeinaie's climate in terms of monthly mean relative performed well given its specific climate. That is, humidity and hours surpassing the temperature and although the ambient environment has surpassed the relative humidity guideline. guideline for a given number of hours, the interstitial Despite being located in rather severe climates sensors only surpassed the guideline for a fraction where the ambient environment surpassed the of those hours. A building with a negative value has guideline for well over 2000 hours, the number of not performed well given its environment. That is, hours the interstitial environment of Group B buildings although the ambient environment only surpassed the surpassed the guideline was only 4 hours. guideline for a specific number of hours, the interstitial The research results suggest that rainscreens are an sensor surpassed the guideline for more hours. effective means to reduce moisture and prevent mold growth in straw bale walls. 3. Results and Discussion Table 2. summarizes the results of the monitoring. 4. Conclusion Of the six buildings monitored, the interstitial The hygrothermal conditions of six straw bale hygrothermal environment of five buildings surpassed structures in Japan were monitored. The purpose of the the 80% relative humidity and 10ºC guideline. present study was to (one) evaluate the potential for The number of consecutive hours the guideline mold growth in the six buildings, (two) clarify moisture was exceeded varies by building. The number of dynamics, and (three) determine the effectiveness of consecutive hours the interstitial environment of Group ventilated rainscreens to control moisture in straw bale B buildings surpassed the guideline was only four walls. (1) The potential for mold growth was found hours. Both of these buildings utilize rainscreens. On to vary by structure. Buildings utilizing rainscreens the other hand, the interstitial environment of three of were found to have a lower risk of mold growth. (2) the four Group A buildings surpass the guideline for Buildings utilizing rainscreens were found to have less over 1000 hours. These buildings have exterior plaster interstitial moisture. Presumably, the use of rainscreens finishes directly applied to bale walls. deflected rain from the plastered straw bale walls, The temperature and relative humidity of the two which in turn reduced interstitial moisture. And (3) sensors from each building that surpassed the guideline the research results suggest that rainscreens are an the greatest number of hours are graphed in Fig.4. effective means to reduce moisture and prevent mold From Group B, only one sensor from Leyenda growth in straw bale walls. surpassed the guideline and no sensors surpassed the guideline from Madeinaie. Although it never surpassed References 1) Bigland-Pritchard, M. (2005) An assessment of the viability of the guideline, Madeinaie's interstitial sensor with the strawbale wall construction in buildings in maritime temperate greatest monthly mean relative humidity, LE, was climates. PhD Thesis, University of Sheffield. chosen to depict Madeinaie's interstitial hygrothermal 2) Carfrae, J., Wilde, P. D., Littlewood, J., Goodhew, S., Walker, P. environment. (2009) Long term evaluation of the performance of a straw bale The monthly mean relative humidity of indoor, house built in a temperate maritime climate. In: 11th International Conference on Non-conventional Materials and Technologies, outdoor and interstitial sensors with the highest NOCMAT 2009, 6-9 September 2009, Bath. monthly mean relative humidity are graphed in Fig.5. 3) Centre for Building Performance Research, Victoria University At some point during the observation period, all of the of Wellington (2010) Table of embodied energy coefficients. Group A buildings' interstitial monthly mean relative Available Online: http://www.victoria.ac.nz/cbpr/documents/pdfs/ humidity surpass the outdoor monthly mean relative ee-coefficients.pd humidity. However, during the observation period, JAABE vol.14 no.1 January 2015 Kyle Holzhueter 211 4) Holzhueter, K. (2011) The hygrothermal environment of straw bale walls in Japan and building practices to control interstitial moisture. PhD Thesis, Nihon University. 5) Holzhueter K. and Itonaga K. (2010) The hygrothermal environment and potential for mold growth within a straw bale wall. Journal of Asian Architecture and Building Engineering, Vol. 9, No. 2, pp.495-499. 6) Holzhueter, K., Itonaga, K. (2014) The influence of passive ventilation on the interstitial hygrothermal environment of a straw bale wall, Journal of Asian Architecture and Building Engineering, Vol. 13, No. 1, pp.223-229. 7) Japan Straw Bale House Association (2009) First straw bale house in Japan. Available Online: http://www.japanstraw.com/index/ main/03hatuno/03hatuno.html 8) Lawrence, M., Heath, A., Walker, P. (2009) The impact of external finishes on the weather resistance of straw bale walls. In: 11th International Conference on Non-conventional Materials and Technologies, NOCMAT 2009, 6-9 September 2009, Bath. Available Online: http://opus.bath.ac.uk 9) Lee, K., Yeom, D., Kim, E. (2013) Experimental research on the correlation of temperature, humidity, and CO level of a rice hull insulated indoor environment, Journal of Asian Architecture and Building Engineering, Vol. 12, No. 2, pp.221-228. 10) Otto, F., Klatecki, M. (2008) B1 Voruntersuchungen durch das Zentrum für Umweltbewusstes Bauen in Kassel. In: Grundlagen zur bauaufsichtlichen Anerkennung der Strohballenbauweise- Weiterentwicklung der lasttragenden Konstruktionsart und Optimierung der bauphysikalischen Performance. Deutsche Bundesstiftung Umwelt, pp.114-293. 11) Thompson, K. (2006) External research program: straw bale construction in Atlantic Canada. Ottawa, Canada: Canada Mortgage and Housing Corporation. 12) Wihan, J. (2007) Humidity in straw bale walls and its effect on the decomposition of straw. Master's Thesis. University of East London School of Computing and Technology. 212 JAABE vol.14 no.1 January 2015 Kyle Holzhueter
Journal of Asian Architecture and Building Engineering – Taylor & Francis
Published: Jan 1, 2015
Keywords: straw bale building; ventilated rainscreens; hygrothermal environment; mold growth; interstitial moisture
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