Open Collections

UBC Undergraduate Research

An investigation into the use of cob and/or straw bale construction in non-residential buildings Kutarna, Matthew; Li, Kevin; Radebe, Ntokozo 2013-04-04

Your browser doesn't seem to have a PDF viewer, please download the PDF to view this item.

Notice for Google Chrome users:
If you are having trouble viewing or searching the PDF with Google Chrome, please download it here instead.

Item Metadata

Download

Media
18861-Kutarna_M_et_al_SEEDS_2013.pdf [ 716.9kB ]
Metadata
JSON: 18861-1.0108469.json
JSON-LD: 18861-1.0108469-ld.json
RDF/XML (Pretty): 18861-1.0108469-rdf.xml
RDF/JSON: 18861-1.0108469-rdf.json
Turtle: 18861-1.0108469-turtle.txt
N-Triples: 18861-1.0108469-rdf-ntriples.txt
Original Record: 18861-1.0108469-source.json
Full Text
18861-1.0108469-fulltext.txt
Citation
18861-1.0108469.ris

Full Text

UBC Social Ecological Economic Development Studies (SEEDS) Student Report       An Investigation Into the Use of Cob and/or Straw Bale Construction in Nonresidential Buildings Matthew Kutarna, Kevin Li, Ntokozo Radebe  University of British Columbia APSC 262 April 4, 2013           Disclaimer: “UBC SEEDS provides students with the opportunity to share the findings of their studies, as well as their opinions, conclusions and recommendations with the UBC community. The reader should bear in mind that this is a student project/report and is not an official document of UBC. Furthermore readers should bear in mind that these reports may not reflect the current status of activities at UBC. We urge you to contact the research persons mentioned in a report or the SEEDS Coordinator about the current status of the subject matter of a project/report”.  UBC Social Ecological Economic Development Studies (SEEDS) Student ReportAn Investigation Into the Use of Cob and/or Straw Bale Construction inNon­residential BuildingsMatthew Kutarna, Kevin Li, Ntokozo RadebeAPSC 262 ­ Sustainability ProjectUniversity of British ColumbiaSubmitted: April 4, 2013To: C. Paterson1ABSTRACTThe University of British Columbia (UBC) Farm is planning on building a new Farm                         Centre to welcome guests and educate visitors. As part of this objective, the UBC Farm wishes                             to investigate straw­bale and cob as potential construction materials. With a major focus on the                           economic and regulatory impacts, this paper examines the effects of these non­traditional                     materials.This analysis take the form of a triple­bottom line assessment; linking the economic,                       social and environmental impacts of the proposed materials. Two case studies were used to                         provide a basis for the analysis; both non­residential buildings of a similar size to the proposed                             UBC Farm Centre. Additionally, primary and secondary research was conducted to quantify the                       findings. Interviews with industry experts were used, as well as a thorough examination of                         academic research.This analysis shows that while straw­bale and cob offer significant economic, social and                       environmental advantages, these are conditional on specific criteria. Regulatory and economic                   concerns suggest that neither straw­bale nor cob should be used as a load­bearing component.                         A timber­frame structure with traditional protective wall­siding is recommended (certain plasters                   could be used); using the straw­bale as the main wall material and cob as a coating on either                                 side. This will allow the UBC Farm to take advantage of the benefits of these proposed materials                               while minimizing any potential for regulatory issues.2TABLE OF CONTENTSLIST OF ILLUSTRATIONS..................................................................................................31.0 INTRODUCTION............................................................................................................52.0 CASE STUDY A ­ DEMMITT COMMUNITY HALL............................................................63.0 CASE STUDY B ­ INSPIRE BRADFORD BUSINESS PARK..............................................74.0 ECONOMIC ANALYSIS..................................................................................................94.1 Cost of Construction 94.2 Lifetime Costs 105.0 SOCIAL ANALYSIS.......................................................................................................125.1 UBC Developmental & Building Regulations 125.2 BC Building Code 125.2.1 Thermal Insulation [Section 9.25.2] 135.2.2 Air Barrier System [Section 9.25.3] 135.2.3 Vapour Barriers [Section 9.25.4] 145.3 LEED Buildings at UBC 166.0  ENVIRONMENTAL ANALYSIS.......................................................................................176.1 Carbon Impact Indicators 176.1.1 Sequestered Carbon 176.1.2 Embodied Carbon 186.2 Operational Indicators 196.2.1 Insulating Properties 196.2.2 Thermal Mass 207.0 CONCLUSION...............................................................................................................217.1 Triple Bottom Line Assessment ­ Economic Analysis 217.2 Triple Bottom Line Assessment ­ Social Analysis 217.3 Triple Bottom Line Assessment ­ Environmental Analysis 217.1 Triple Bottom Line Assessment ­ Conclusion 218.0 RECOMMENDATIONS...................................................................................................228.1 Economic 228.2 Social 22REFERENCES.....................................................................................................................233LIST OF ILLUSTRATIONSTable 1 ­ Results of Vapour Permeance Test Results............................................................15­16Figure 1 ­ Total house materials CO2 emissions.........................................................................18Table 2 ­ Materials required for construction and associated embodied energies.......................1941.0 INTRODUCTIONThe UBC Farm, as part of its organizational goals, sets high standards for environmental                         and social sustainability. These standards manifest themselves in the UBC Farm’s proposed                     plan to build a new UBC Farm Centre; a building for education and social exchange. This centre                               will be roughly 2500 to 3000 m2and contain a variety of different spaces including classrooms,                             meeting spaces, eating areas and kitchens.The UBC Farm wishes to investigate the possibility                       of using straw­bale and cob as building materials for this new centre.A triple bottom line assessment has been conducted in order to determine the economic,                         social and environmental impacts of There are well­known environmental benefits to using these                       non­traditional materials; as such, this analysis focuses more heavily on the economic and                       regulatory impacts of these construction materials. The economic analysis centers on the                     indicators of initial construction cost and long­term operating costs. The social aspect is based                         on a safety perspective and any regulatory concerns enacted by UBC’s adherence to the British                           Columbia Building Code (BCBC). Finally, the environmental impacts are measured through the                     energy saved through carbon sequestration, embodied carbon and the operational energy                   savings from improved thermal insulation.The main goal of this analysis is to provide a recommendation to the UBC Farm about                             straw­bale and cob as a construction material for the new UBC Farm Centre. Much of the                             information and comparisons are taken from non­residential buildings of a similar size using                       straw­bale and cob, as these will most closely mimic the construction and operational                       requirements.52.0 CASE STUDY A - DEMMITT COMMUNITY HALLFor our first case study, we are going to look at the Demmitt Community Hall in Demmitt,                               Alberta. We decided that this would be a very relevant case study, as the building is situated in a                                   nearby Canadian province and has a fairly large footprint. On June 10, 2010, the construction of                             a new community hall situated in Demmitt was announced by the department of Western                         Economic Diversification Canada (“Canada’s economic action”, 2010). In addition to providing                   short­term employment to the town of Demmitt during the construction period, the new                       community hall was also expected to provide long­term economic benefits to local businesses                       through the hosting of various events. As a part of Canada’s Economic Action plan, the federal                             government was set to fund half of the estimated $1 million that was needed for the construction                               of the 4000 sq. ft. community hall (“Canada’s economic action”, 2010). This is a very modern                             building with amenities such as a kitchen, stage, dressing rooms, and a hardwood dance floor.                           As a public building, the Demmitt Community Hall is required to be compliant with commercial                           building standards such as test based engineering standards and a two hour rating for the                           plasters and walls (Gonzalez, H.J. (March 22, 2013).Email interview).From its inception, the Demmitt Community Hall was constructed with sustainability and                     longevity in mind. According to the President of the Demmitt Cultural Society, Peter von                         Tiesenhausen, the building is “built to last 100 years” and will use “local building materials and                             advanced sustainable practices” in the process. (“Canada’s economic action”, 2010) The basic                     structure of the building consists of a timber frame with straw bale walls coated in wire and                               stucco (Plummer & Parklander, 2011. A significant portion of the wood that was used for the                             timber frame was sourced from local trees that were already killed by the mountain pine beetle                             (Plummer & Parklander, 2011). In addition to sourcing local construction materials, solar were                       also used as an additional source of heating for the building. To improve the insulation of the                               building and reduce the cost of heating, a Structural Insulated Panel (SIP) from Greensmart                         Manufacturing was used. In addition to the local craftsmen and members of a regional college                           were hired, around 34 local volunteers were present over one long weekend to assist the                           construction. The Demmit Cultral Society announced the opening of the Demmitt Community                     Hall on September 5, 2011 for an estimated $1.28 million (“Canada’s economic action”, 2010).63.0 CASE STUDY B - INSPIRE BRADFORD BUSINESS PARKThe Inspire Bradford Business Park is an eco­friendly business park located in Bradford,                       West Yorkshire, England. It was constructed using straw bale wall panels. This building was                         selected as a case study, for this report, as it has a similar footprint to that proposed for the UBC                                     Farm centre. It was also constructed in adherence to the BREEAM construction standards,                       which is the British equivalent to the LEED (Newlands Community Association, 2012).The Inspire Bradford Business Park demonstrates the presently uncommon, yet                 effective, use of straw bale in the provision of commercial property. It is comprised of 18 service                               offices and 14 workspaces, for small businesses and startups, and a community facility housed                         in two buildings covering a surface area of 2787 square metres. Construction began in April                           2011, taking 36 weeks to finish. The facility opened in October 2012 (Newlands Community                         Association, 2012). The cost of the project was £4 million. The project received additional                         funding from various organizations, which include the European Union (£1.019 m), the UK                       government’s Community Builders Fund (£1.38 m), Bradford’s Newlands Community               Association and Local Enterprise Growth Initiative (£990k), and additional funding was obtained                     through a £1m from the Charity Bank (Wainwright, 2010).The development of the facility incorporated environmentally sound construction methods                 that aimed to achieve a BREEAM Excellent rating for energy efficiency. It was built using 260                             thermally efficient, 48 cm thick, prefabricated straw bale wall panels developed by ModCell. A                         panel is composed of a wooden frame filled with spray­plastered lime straw bales (Offin, 2010).                           The benefits of using these wall panels is that they have a U­value of 0.13 to 0.19 ­ well below                                     the UK regulatory standard of 0.35 – a fire performance of 2 hours and 15 minutes, and a sound                                   reduction of 50 dB (ModCell, 2011). The use of prefabricated wall panels, which are constructed                           in controlled factory conditions and then transported to the construction site, is particularly                       advantageous as it alleviates the susceptibility of straw bale to moisture, which can lead to                           rotting, and a lack of uniformity found in traditional straw bale walls (Offin, 2010).700 rolls of thermal and acoustic insulation, manufactured using fibers from waste                     denim, were used. This insulation is free of chemical irritants, such as melamine or phenolic                           7resins. It also meets the highest UK testing standards for fire and smoke ratings, fungi                           resistance and corrosiveness (Newlands Community Association, 2012). 50% of the site’s                   electricity requirements are generated by 36 kW photovoltaic cells located on the roofs of the                           buildings. 50% of the water requirements are satisfied by a rainwater catchment reservoir                       (ModCell, 2011).One of the major successes of the business park is sustainability in energy and water                           consumption. Prior to the completion of the project, preliminary calculations showed the energy                       usages as follows (Newlands Community Association, 2012). :● Energy consumption: 84.25 kwh per square metre● Fossil fuel consumption: 0● Renewable energy generation: 14.31 kwh per square metre● Water use: 4 cubic metres per person per year.84.0 ECONOMIC ANALYSISIn conducting an economic analysis of the proposed cob and straw New Farm building                         we wanted to determine the economic feasibility of a project of this scale based cost                           estimations. In order to do so, we decided to assess not only the costs associated with the                               construction of the building, but also the cost of maintaining such a building. In addition to the                               conducting research, we also talked to two experts in order to gain a greater into the costs                               involved with cob and straw bale construction. The first person that we got in contact with was                               Mr. Habib Gonzalez, a bale construction consultant for Sustainable Works. Our second contact                       was Michael Chiang, a licensed real estate agent who has been involved with residential                         construction projects.4.1 Cost of ConstructionOne of the benefits of utilizing cob and straw as a building material is ability to source                               local materials. The benefit of doing so is that the cost of transporting building materials can be                               significantly reduced. Our research revealed that a local bale of straw with a height of 14”, a                               width of 18”, and a 35­40” length can be sourced for a cost of $7.95 (“Vanderveen hay sales ltd”,                                   2013). Based on the research done by R.H. Saxton of the University of Plymouth, typical cob                             mixtures consist of 30% gravel, 35% sand, 35% silt and clay with a permitted 10% deviation                             (Saxton, 1990). While it may be possible to use the soil within the construction site for the cob                                 mixture, it is very likely that a small amount of the materials above will have to be purchased in                                   order to achieve the right cob consistency. Tests will have to be conducted on the soil samples                               of the UBC Farm in order to assess the soil content.In the context of our building cost analysis, basic costs include the frame of the building                             and straw bale walls that will be used to cover the building. Based the information provided by                               Mr. Gonzalez and Mr. Chiang, the basic costs of materials and design is highly dependent on the                               design details and complexity of the building. Mr. Gonzalez believes that local designers would                         give estimate of $15 ­ $20 per sq. ft. for a building with exterior bale walls and a building permit                                     9(Gonzalez, H.J. (March 22, 2013). Email interview). Note that this figure does not include the cost                             of electrical wiring, sewage, the cob layer, or waterproofing costs. Possible ways of reducing the                           complexity of the building design would include minimizing the use of windows, or the utilization                           of a traditional rectangular shape for the structure. Further cost savings of course can be                           realized with the use of salvaged material such as wood beams or doors.One of the most significant cost of any construction project is labour. Based on our                           conversation with Mr. Gonzalez, the Demmitt Community Hall project had 6 full time workers that                           were comprised of local tradesmen and students (Gonzalez, H.J. (March 22, 2013). Email                       interview). In addition to the 6 full time workers, there were also two or three volunteer workers                               that worked within the job site. Based on the information provided by both Mr. Gonzalez and Mr.                               Chiang, the amount of workers that are required for a project is highly dependent on the                             complexity of the project and the efficiency of the construction crew (Chiang, M. (March 31,                           2013). Personal interview). With the assumption that the proposed New Farm building will have a                           complexity that is similar to that of the Demmitt Community hall and a footprint that is close to                                 the Inspire Bradford Business Park, we believe that the building will require a design and                           construction period of around approximately 36 weeks Newlands Community Association, 2012).                   Based on Mr. Chiang’s previous projects, the cost of hiring a local construction worker will cost                             an estimated $15 per hour with an 8 hour work day (Chiang, M. (March 31, 2013)).4.2 Lifetime CostsWhile initial construction cost may be a sufficient economic indicator in most cases, the                         lifetime cost of maintaining a building is also a crucial factor in the triple bottom line assessment.                               We believe that cob and straw buildings will have an advantage in terms of lifetime costs based                               on their history of longevity and high level of insulation.In certain parts of England, cob­based houses have existed for centuries with most being                         between 100 and 400 years old (Saxton, 1990). The Demmitt Community hall from the first case                             study was designed to last for 100 years (“Canada’s economic action”, 2010). We believe that                           with the use of either cob or straw bale (or a hybrid of the two materials) in the construction of                                     10the New Farm building, existing buildings built with these materials are capable of lasting for                           many decades.As we discovered during the environmental analysis of cob and straw construction, we                       found that straw bales do have a higher insulation efficiency value compared to both cob and                             traditional construction materials (Stone, 2003). According to a study conducted by Canada                     Mortgage and Housing Corporation (CMHC), they found that “straw bale homes used an average                         of 20% less heating energy” in the 11 straw bale homes that they studied (Stone, 2003). Given                               the expected longevity and the large footprint of the proposed building, we believe that this                           insulation efficiency will present long term cost savings from the decrease in energy required for                           heating.115.0 SOCIAL ANALYSISThe following presents a discussion into the regulatory concerns associated with cob                     and straw bale construction. The relevant building standards and regulations enforced by                     provincial legislation, and by the university, will be examined and the feasibility of the building                           materials to satisfy those requirements will be assessed with regards to their engineering                       properties.5.1 UBC Developmental & Building RegulationsUBC upholds the British Columbia Building Code for all building and construction on the                         UBC Vancouver campus. The Leadership in Energy and Environmental Design rating system is                       also enforced at UBC, as UBC is a member of the Canada Green Building Council. These                             systems have been put into place to ensure the health, safety and protection of persons and                             property, and in pursuit of a campus of high­performing green buildings at the university (UBC,                           2013).5.2 BC Building CodeThe 2012 BCBC is an objective­based code, which identifies the minimum standard                     within the Province of British Columbia for buildings to which this code applies. The BCBC                           establishes requirements to address the following five objectives:● Safety● Health● Accessibility for persons with disabilities● Fire and structural protection of buildings● Energy and water efficiencyThe BCBC should not be considered as a textbook on the design or construction of                           buildings and facilities, nor is it the only document regulating health and safety. It establishes the                             12criteria that materials, products and assemblies must meet (Office of Housing & Construction                       Standards, 2012).While earthen construction methods have been in use for many centuries, presently, the                       challenge exists in assessing earthen building materials, such as cob and straw bale, in                         accordance to modern day regulations. In the BCBC, particular focus is made on the                         conventional construction methods using concrete, wood and metallic building materials.                 Unconventional methods must be able to moisture and thermal performance standards, namely                     the regulations pertaining to moisture and thermal performance requirements. The challenge                   present in this task is that cob and straw, or other earthen building materials, are not recognized                               by the code and it uses metrics that do not readily apply to earthen building systems.                             (Eco­Sense, 2011). Section 9.25 of the BC Building Code contains the standards and                       regulations pertaining to heat transfer, air leakage, and condensation control.5.2.1 Thermal Insulation [Section 9.25.2]The BCBC states that: “all walls, ceilings and floors separating heated space from                       unheated space, the exterior air or the exterior soil shall be provided with sufficient thermal                           insulation to prevent moisture condensation on their room side during the winter to ensure                         comfortable conditions for the occupants.” (Office of Housing & Construction Standards, 2012)The Greater Vancouver region has 2631 heating Degree days per year (The Weather                       Network, 2013). For framed wall assemblies in this region, walls must be a minimum of R13.06                             (or 2.30 RSI, < 4000 HDD) (Office of Housing & Construction Standards, 2012). The thermal                           resistance of a cob wall largely depends on its assembly.● Cob walls traditionally have an R­value of 0.60/inch, with the wall assembly being a                         nominal 24 inches, or 61 cm, thick. A wall of 28 inches, or 71 cm, would be required to                                   meet the code (Eco­Sense, 2011).● Straw­bale, at standard densities, achieves R­values of 2.40 to 2.77 per inch (Commins,                       1998). A wall of above 5.50 inches is sufficient to meet the code.5.2.2 Air Barrier System [Section 9.25.3]The BCBC stipulates that: “wall, ceiling and floor assemblies (separating conditioned                   13space from unconditioned space or from the ground) shall be constructed so as to include an air                               barrier system that will provide a continuous barrier to air leakage. From the interior of the                             building into wall, floor, attic or roof spaces, sufficient to prevent excessive moisture                       condensation in such spaces during winter (Office of Construction & Housing Standards, 2012).Cob naturally provides a continuous air barrier due to its monolithic structure. However,                       this air barrier must be continued in the areas where cob meets other assemblies, namely the                             roof structure. It is good practice to have an earth­ or lime­based plaster applied to the exterior                               and interior of the walls (Fratalocchi et al, 2010). For straw bale assemblies, all wet­applied                           monolithic plaster finishes are sufficiently air impermeable to control airflow (Straube, 2000).5.2.3 Vapour Barriers [Section 9.25.4]The BCBC asserts that: “thermally insulated wall, ceiling and floor assemblies shell be                       constructed with a vapour barrier so as to provide a barrier to diffusion of water vapour from the                                 interior into the wall spaces, floor spaces or attic or roof spaces.” (Office of Housing &                             Construction Standards, 2012)Based on the findings of researchers John Straube and Gernot Minke,● cob has a permeance of  1088 ng/(Pa​∙s∙​m2),● lime plasters have a permeance rating of 500 ng/(Pa∙​s∙​m2),● and earthen plasters have a permeance of 1200 ng/(Pa​∙s​∙m2) (Eco­Sense, 2011).● A 1 meter thick layer of straw bale is expected to have a vapor permeance of 50 to 100                                   ng/(Pa∙s∙m2)● and a 450 mm thick layer of straw bale should have a permeance of approximately 110 to                               220 ng/(Pa∙​s∙​m2) (Straube, 2000).In Section 9.25.5.1 of the BCBC, it goes on to state that “… a water vapour permeance                               less than 60 ng/(Pa​∙s​∙m2) when measured in accordance with ASTM E 96/E 96M, ‘Water Vapor                           Transmission of Materials,’ using the decant method” is required (Office of Housing &                       Construction Standards, 2012).It is this section of the code that presents the biggest challenge. For the case of cob,                               historical evidence has shown its effectiveness when combined with interior and exterior plaster                       14(Fratalocchi et al, 2010). It can be shown that cob excels in this aspect despite the metrics being                                 incongruent between the code’s vapour permeance standards and actual performance                 (Eco­Sense, 2011). However, since the BCBC is strictly enforced at UBC, it is recommended                         that cob be used in a wall assembly that can satisfy this requirement and where it is not the sole                                     nor largest component of the assembly.Straw bale, while being less permeable than cob, as previously mentioned, is still very                         vapour and water permeable and, thus, relies on plaster to control the entry of these sources of                               moisture. The ability of an exterior plaster to absorb and store moisture is critical in preventing                             moisture from being transported inward to the straw bales. In consequence, the vapour                       permeability, or permeance, should be of no practical importance since excessive moisture                     should not be allowed to come into contact with the straw bales (Straube, 2000). Based on the                               following table, it is recommended that a straw bale wall assembly should consist of plaster                           composed of cement bonded sand which will satisfy the vapour permeance requirement of the                         BCBC.Sample Thickness [mm] Permeance[ng/(Pa∙​s∙​m2)]Permeability [ng/(Pa∙​s∙​m)Cement:Sanddatum 43.5 39 1.7elastomeric coating 39.5 40 ­­siloxane 41.0 40 1.7Cement:Lime:Sanddatum 35 295 10.3linseed 36 223 8.0elastomeric coating 32.5 244 ­­siloxane 41 203 8.3calcium stearate 53.5 81 4.3calcium stearate 44 142 6.2calcium stearate 53.5 41 2.2latex paint 36.5 203 ­­15oil paint 40 41 ­­Cement:Lime:Sanddatum 50.5 295 14.9linseed 50.5 259 13.1Lime:Sanddatum 33.5 565 18.9datum 35.5 529 18.8quicklime 32 459 14.7Table 1: Reults of Vapour Permeance Test Results (Straube, 2000)Results of a series of vapour permeance and water uptake tests on a range of plaster finishes that hadbeen applied to straw bales. Samples were all lime or cement bonded.5.3 LEED Buildings at UBCAll publicly­owned new construction and major renovation projects over 600 m2 in British                       Columbia must achieve LEED Gold certification. UBC has enacted upon the LEED rating                       system and has green building policies to ensure that sustainable practices are followed and                         implemented in­line with the university’s targets (UBC, 2013). The UBC LEED Implementation                     Guide for LEED Canada Building Design + Construction 2009 can be viewed for further                         reference.166.0  ENVIRONMENTAL ANALYSISIn order to properly assess the environmental impacts of the use of straw­bale and cob                           materials for construction, proper indicators must be chosen with which to evaluate these                       materials. By examining the differences between traditional construction materials and the                   proposed materials, these indicators will determine whether there is a benefit to switching. The                         main indicators we will use are the CO2ratings based on creation and construction, and the                             on­going performance of the materials. In order to quantify this, we will investigate the                         sequestered and embodied carbon ratings, the insulation properties and the thermal mass of the                         proposed materials. Sequestered carbon and embodied carbon (or embodied energy in general)                     are well­known measures of the initial costs and benefits for a material (Hammond & Jones,                           2008), where as insulation and thermal mass provide a proxy for operational impacts.6.1 Carbon Impact Indicators6.1.1 Sequestered CarbonSequestered carbon is a measure of the theoretical amount of CO2gas trapped in the                           material through its creation process. This is often quoted when speaking of wood constructions;                         wood captures (sequesters) carbon dioxide as a plant, effectively trapping that gas in the                         material. And so, sequestered carbon represents the opposite of carbon emission during                     formation. Straw­bale, as a plant based material, sequesters a significant amount of carbon; this                         is a significant benefit. Depending on the type of straw used (which plant), 29% by mass of                               straw­bale is sequestered carbon (Alcorn & Donn, 2010). If using a more theoretical model,                         carbon dioxide sequestration may be as high as 52% by mass (Sodagar et al., 2011). Accurate                             data for cob sequestration are not available for every soil composition, however soil from less                           temperate northern climates may contain 31% to 40% carbon dioxide by mass (Milutienne et al.,                           2007). Most non­organic materials sequester no carbon dioxide; this carbon offset is a significant                         change.As seen below, the use of plant­based materials, such as timber and straw­bale, can                         significantly decrease the carbon impact of construction; in some cases the sequestered carbon                       17offsets the initial carbon costs.Figure 1 ­ Total house materials CO2 emissions of one of the houses with different external walling systems(Sodagar et al., 2011)6.1.2 Embodied CarbonSimilarly, embodied carbon (EC) is a more complete measure of the carbon emissions                       of a material, through its entire life­cycle. EC takes into account the energy required to create the                               material, store it, transport it and prepare it for construction, as well as any emissions or capture                               that occurs during the material’s operational life. The major advantage of using cob as a                           construction material is that it is available locally – potentially on­site at the UBC Farm – meaning                               the transportation portion of the EC is minimal. Straw­bale, depending on the source, has an EC                             value of 0.91 MJ/kg, versus an EC value of 15 MJ/kg for plywood or 4.6 MJ/kg for cement (Offin,                                   2010). The EC value for cob is much higher than that of straw­bale, mainly because of how                               much more work­intensive it is; there is a significant mixing step, coupled with the possible                           additives (sand, gravel, clay) that are required to create the right mix (Carfrae, 2009). Values                           between 5.3 and 6.8 MJ/kg are common for cob (Offin, 2010).18Table 2 ­ Materials required for construction of 1m x 2.4m section of exterior wall in straw bale house andembodied energies associated with them  (Offin, 2010)6.2 Operational Indicators6.2.1 Insulating PropertiesIn order to evaluate the environmental impact of these construction materials                   post­construction, a measure of the carbon emissions of the structure is required. The main                         contributors to operational carbon of structures are heating and power (the power systems                       within the building are not relevant to this research). Thus, any change in heating efficiency of a                               structure will serve as a good proxy of the carbon emissions when using the proposed materials.                             The insulating properties of a material provide a direct correlation to the amount of energy                           expended in heating a building as it tracks the amount of energy lost to the environment. Often,                               thermal insulation is measured using the R­value of thermal resistance, where a higher value                         insulates better. Straw­bale provides very good thermal insulation, achieving values of R2.4 to                       R2.77 per inch for standard straw­bale densities (Commins, 1998). Special straw­bale packing,                     19with higher density, can drop the value to as low as R0.94 per inch (Stone, 2003). Cob provides                                 poor thermal insulation, with a value of between R0.30 and R0.63 per inch, with R0.60 being the                               most common (Stone, 2003).6.2.2 Thermal MassIn like manner, thermal mass correlates well with heating­energy; it is a measure of the                           amount of heat energy a material can store per unit mass (or per unit volume). A material with a                                   high thermal mass will store more energy, allowing excess energy to be captured and released                           as the temperature fluctuates. In other words, higher thermal mass allows a material to store                           more energy – in basic terms the material will cool the building when it is hot outside and provide                                   heat when it is cold. Cob has a high thermal mass because of its relative density (Chalfoun,                               2003), however an exact value is difficult to determine given the variety of methods used to                             measure thermal mass. Straw­bale, given its relatively low density, provides very little thermal                       mass(Chalfoun, 2003). One method of measuring the thermal mass of a material is based on its                             volumetric specific heat capacity. Straw­bale has a value of about 250 kJ/m3K while cob has the                             much higher value of 1900 kJ/m3K (Atkinson, 2008).207.0 CONCLUSION7.1 Triple Bottom Line Assessment - Economic AnalysisThere exist significant economic benefits to using straw­bale and cob for construction of                       the new UBC Farm Centre. These are demonstrated by the difference of initial construction                         costs, as well as long­term savings associated with the reduced heating requirements.                     However, many of these costs are contingent on an appropriate labour force and design                         experience during the planning and construction phases.7.2 Triple Bottom Line Assessment - Social AnalysisFrom a regulatory perspective, there are no direct restrictions on the use of straw­bale                         and cob in construction at UBC (or in BC). However, BC Building Code requires that standards                             for thermal insulation, air barriers and vapour barriers be met. Straw­bale will allow the                         construction to meet code for thermal insulation, however the vapour and air barriers must be                           made of a different material. There are also concerns when using straw­bale or cob as a                             structural (load­bearing) material.7.3 Triple Bottom Line Assessment - Environmental AnalysisStraw­bale and cob present a significant environmental benefit when used. Not only do                       they sequester carbon, the energy involved in their creation and life­cycle is very low compared                           to traditional materials. Additionally, they present an operational advantage when factoring in the                       heating energy savings over the long­term.7.1 Triple Bottom Line Assessment - ConclusionThis analysis shows that the use of straw­bale and cob as construction materials                       provides meaningful economic and environmental benefits. These economic benefits can be                   maximized with proper design considerations. However, there exist some regulatory concerns                   which limit their use to wall mass and other non­load­bearing roles. Overall, we recommend that                           straw­bale and cob be used in the construction of the new UBC Farm Centre.218.0 RECOMMENDATIONSThis analysis confirms the recommendation of using straw­bale and cob in the                     construction of new UBC Farm Centre, with certain conditions, listed here below.8.1 EconomicThe economic benefits can be maximized if the design of the building is simplified as                           much as possible in addition to using traditional structural components (such as timber). This                         will minimize the design costs associated with getting an engineer to sign off on a construction                             with non­traditional materials. In order to minimize costs associated with length of construction,                       labourers or consultants experienced with straw­bale and cob use are preferred. Where                     possible, materials should be sourced locally; straw­bale from suppliers in the Lower Mainland,                       cob on­site if the soil is of the proper composition and timber from BC forests (possibly                             pine­beetle killed wood).8.2 SocialIn order to meet the specifications of the BC Building Code, we recommend that the                           structural components of the building be made of timber, that straw­bale and cob be used as                             wall material, and that plaster be used as a vapour and air barrier for the walls. A wet­applied                                 monolithic plaster finish is necessary for the air barrier, while any cement­bonded plaster is                         sufficient for the vapour barrier. Given their mechanical and thermodynamic properties,                   straw­bale and cob are not suitable to be used as structural components for large buildings, nor                             as seal layers in exterior walls.22REFERENCES[1] Alcorn, A., & Donn, M. (2010). Life cycle potential of strawbale and timber for carbon sequestration inhouse construction. Retrieved from the University of Welllington website:http://www.claisse.info/2010%20papers/m23.pdf[2] Atkinson, C. (2008). Energy assessment of a straw bale building. Retrieved from University of EastLondon, Advanced Environmental and Energy Studies website:http://homegrownhome.co.uk/pdfs/Energyassessmentofastrawbalebuilding.pdf[3] Carfrae, J. (2009). Long term evaluation of the performance of a straw bale house built in a temperatemaritime climate. Retrieved from University of Plymouth ARCOM Doctoral Research Workshopwebsite: http://www.arcom.ac.uk/­docs/workshops/2009­Plymouth.pdf#page=28[4] Commins, T., Stone, N. (1998). Tested r­value for straw bale walls and performance modeling for strawbale homes. California Energy Commission.[5] Eco­Sense. (2011). BC building code. Retrieved fromhttp://ecosenseliving.wordpress.com/2011/09/ecosense.bc.building.code.pdf[6] Fratalocchi, E., Pasqualini, E., Stazi, A., & Quagliarini, E. (2010). Cob construction in Italy: somelessons from the past. Sustainability, 2, 3291­3308. doi:10.3390/su2103291[7] Hammond, G.,& Jones, C. (2008). Embodied energy and carbon in construction materials.Proceedings of the Institution of Civil Engineers ­ Energy, 161(2). 87­98. ISSN 1751­4223[8] Milutienne, E., Jurmann, K., & Keller, L. (2007). Straw bale buildings ­ reaching energy efficiency andsustainability in northern latitudes. Retrieved from the Renewable Energy Information ConsultationCentre website: http://siaudunamai.lt/downloads/NORTH%20SUN%202007%20paper%20STRAW%20BALE%20BUILDING.pdf[9] ModCell. (2011). Projects: inspire Bradford business park. Retrieved fromhttp://www.modcell.com/projects/inspre­bradford­business­park[10] Newlands Community Association. (2012). Inspire Bradford business park ­ case study. Retrieved from23http://www.eco­fair.co.uk/wp­content/uploads/Inspire­Bradford­Case­Study.pdf[11] Office of Housing & Construction. (2012). British Columbia Building Building Code Section 9.25.[12] Offin, M. (2010). Strawbale construction: assessing and minimizing embodied energy (Master’s Thesis).Retrieved from https://qspace.library.queensu.ca/[13] Plummer, E., & Parklander, H. (2011, June 17). New Demmitt community hall complete. Daily HeraldTribune. Retrieved fromhttp://www.dailyheraldtribune.com/2011/06/17/new­demmitt­community­hall­complete[14] Saxton, R. H. (1995). The performance of cob as a building material. The Structural Engineer, 73(7),111­115.[15] Sodagar, B., Rai, D., Jones, B., Wihan, J., & Fieldson, R. (2011). The carbon­reduction potential ofstraw­bale housing. Building Research & Information, 39(1), 59­65.doi: 10.1080/09613218.2010.528187[16] Stone, N. (2004). Thermal performance of straw bale wall systems. Ecological Building Network(EBNet). Retrieved March 15, 2013, from http://cd2e­lmcu.vertuoze.fr/sites/default/files/annuaires/[17] Straube, J. (2000). Moisture propertie of plaster and stucco for strawbale buildings. Retrieved fromhttp://homegrownhome.co.uk/pdfs/Straube_Moisture_Tests.pdf[18] University of British Columbia. (2013). LEED @ UBC. Retrieved fromhttp://www.sustain.ubc.ca/campus­initiatives/buildings/leed­ubc[19] Vanderveen hay sales ltd. (2013, March 27). Retrieved from http://www.vanderveenhay.com/Prices.html[20] Wainwright, M. (2010). Work begins on Europe’s largest strawbale building. Retrieved fromhttp://www.guardian.co.uk/environment/2010/02/europe­largest­straw­building[21] The Weather Network. (2013). Statistics: Vancouver, BC. Retrieved fromhttp://www.theweathernetwork.com/statistics/degreedays/cl1108446/cabc0308[22] Western Economic Diversification Canada, (2010).Canada’s economic action plan supports communityinitiative in Demmitt. Retrieved from website: http://www.wd.gc.ca/eng/77_12066.asp24

Cite

Citation Scheme:

        

Citations by CSL (citeproc-js)

Usage Statistics

Share

Embed

Customize your widget with the following options, then copy and paste the code below into the HTML of your page to embed this item in your website.
                        
                            <div id="ubcOpenCollectionsWidgetDisplay">
                            <script id="ubcOpenCollectionsWidget"
                            src="{[{embed.src}]}"
                            data-item="{[{embed.item}]}"
                            data-collection="{[{embed.collection}]}"
                            data-metadata="{[{embed.showMetadata}]}"
                            data-width="{[{embed.width}]}"
                            data-media="{[{embed.selectedMedia}]}"
                            async >
                            </script>
                            </div>
                        
                    
IIIF logo Our image viewer uses the IIIF 2.0 standard. To load this item in other compatible viewers, use this url:
https://iiif.library.ubc.ca/presentation/dsp.18861.1-0108469/manifest

Comment

Related Items