Straw Bale Construction Research Articles

Transformational green sustainable concepts in the field of infrastructure

In this comprehensive study, we explore the multifaceted world of green sustainable construction, highlighting innovative techniques and materials. This article presents an insightful exploration of green sustainable construction, focusing on the crucial aspects of architectural design, judicious material selection, and the adoption of optimal structural designs. Through comprehensive literature research supplemented by practical examples, it highlights several innovative construction methodologies that are at the forefront of green sustainable development. These include the use of lightweight framing, cladding systems, autoclaved aerated concrete (AAC), rammed earth, and straw bale construction, each contributing uniquely to environmental sustainability. The study brings to light the looming issue of raw material scarcity due to excessive exploitation, urging for sustainable material management in construction. It stresses the urgency of implementing effective pollution control measures within the construction sector, asserting that such practices are not just beneficial but essential for environmental conservation and sustainable development. This research contributes significantly to the field by providing a foundation for future exploration and advancements in sustainable construction practices.

Straw bale construction towards nearly-zero energy building design with low carbon emission in northern China

With the aim of achieving carbon neutrality, bio-based construction is of increasing interest for decarbonization globally. Among the potential candidates, straw bale is promising due to its ready availability and energy efficiency benefits. However, thermal conductivities of straw bales can vary greatly due to construction details, which may lead to failures in meeting nearly-zero energy building (nZEB) design standards in real practice. In the context, this study applied thermal property and carbon emission assessment of full-size straw bale walls (SBWs) and construction of an experimental building in northern China. The results demonstrated that the thermal conductivities of different monitoring portions of the SBWs ranged from 0.067 to 0.088 W·m−1·K−1. This resulted in U-values (0.16 W·m−2·K−1) marginally higher than the lower limits of nZEB design, indicating the importance of addressing thermal bridging issues of SBWs. The SBWs without additional insulation layers therefore can satisfy nZEB design standards in the severe cold region after certain adjustments. Besides, when not accounting for carbon sequestration, SBWs generated the lowest emissions among the schemes in meeting U-value limits for nZEB design (at least 14.6% lower than those of timber walls), with increasing emission reductions as U-value limit decreased. The results indicated that SBW demonstrated effectiveness in carbon reductions with high thermal performance. The findings of the research can facilitate application of straw bales and development of clean construction and net-zero design in northern China.

A long-term monitoring study on the thermal comfort and durability of a straw bale Passivhaus cottage

The built environment sector accounts for 40% of the UK's total carbon footprint; bio-based construction materials can play an important role in reducing the whole-life carbon of a new build. Straw bale construction is one of the most promising bio-based methods of construction, due to its availability and material properties. Among the declared benefits of straw bale construction are the internal regulation of heat and moisture and the ability of the fabric to dry out. This paper presents a long-term monitoring study aimed at understanding the indoor temperature and moisture balance of a straw bale cottage built in the UK to a near Passivhaus level. The study lasted 6 years, monitoring the temperature and relative humidity of the indoor and outdoor environments, and in ten locations within the straw bale walls. The analysis has shown that the indoor environment achieved thermal comfort throughout the monitoring period, even when the building was used intermittently. Also, an analysis of surface temperatures and a mould growth risk analysis identified very limited mould growth risk within the building fabric. This paper shows the potential of straw bale low-energy construction in providing thermal comfort and a durable building fabric while minimising the whole-life carbon of buildings.

A Mini-Review on Straw Bale Construction

Straw bale building construction is attracting a revived public interest because of its potential for reduced carbon footprint, hygrothermal comfort, and energy savings at an affordable price. The present paper aims to summarize the current knowledge on straw bale construction, using available data from academic, industry, and public agencies sources. The main findings on straw fibers, bales, walls, and buildings are presented. The literature shows a wide variability of results, which reflects the diversity of straw material and of straw construction techniques. It is found that the effective thermal conductivity, density, specific heat, and elastic modulus of straw bales used in construction are in the range 0.033–0.19 W/(m·K), 80–150 kg/m3, 1075–2000 J/(kg·K), and 150–350 kPa respectively. Most straw-based multilayered walls comply with fire resistance regulations, and their U-value and sound reduction index range from 0.11 to 0.28 W/m2 K and 42 to 53 dB respectively, depending on the wall layout. When compared to standard buildings, straw bale buildings do provide yearly reductions in carbon emissions and energy consumption. The reductions often match those obtained after applying energy-saving technologies in standard buildings. The paper ends by discussing the future research needed to foster the dissemination of straw bale construction.

Shear behaviour of reinforced straw-bale plaster sheathed cold-formed steel-framed shear walls

The introduction of cold-formed thin-walled steel (CFS) framed systems into straw-bale construction is a new development construction. A CFS stud frame without blocking or strap-brace provides little in-plane shear stiffness, however it can provide lateral support for the thin and low-reinforcement sheathing through self-tapping screw anchorage, allowing the sheathing to subject to shear failure rather than buckling failure. Straw-bales with different thicknesses can satisfy different requirements for heat transfer and sound insulation. Since straw-bales are reliably bonded to the sheathing, the straw-bales can provide lateral support for the thin sheathing and can also effectively slow down the decline of the shear strength after the sheathing cracks. Moreover, the anchorage slip and the shear deformation of the sheathing material are the major factors affecting shear stiffness. The theory presented in this paper predicts the shear deformation response of the reinforced straw-bale plaster sheathed CFS framed shear wall specimen. The behaviour of the self-tapping screw anchorage was defined using power curve to predict the wall deformation due to anchorage slip. The deformation caused by shear in the sheathing material was estimated using refined softened truss model, which was based on the mechanical equilibrium condition, strain compatibility condition, and the constitutive relationship of softened cement mortar and mesh wire embedded in cement mortar. Comparing the theoretical results with the experimental data, the two were in good agreement. The shear strength of different configurations of reinforced straw-bale walls described in the literature were estimated, which proved the applicability of the theory. • Introduction of cold-formed thin-walled steel (CFS) framed system into straw-bale construction. • Estimation of the two major factors affecting the wall shear stiffness. • Validation of the predicted results according to experimental data. • Prediction for the shear strength of reinforced plaster straw-bale walls with different configurations.

Hygrothermal performance, energy use and embodied emissions in straw bale buildings

Straw bale is a low embodied energy and technically acceptable thermal insulation material. As per today, there is a lack of standardized technical data on utilizing straw bale in building construction, while the existing research studies rather focus on limited specific experimental or computational scenarios without summarizing in an organized way the behaviour of straw bale construction under different climate conditions and assembly configurations. This comparative study presents systematically the hygrothermal and energy performance of straw bale buildings with different exterior cladding and finishing mortar or sheathing board, exposed in various representative climates. The findings provide an insight into the optimal selection of materials and furthermore highlight the importance of climate adaptation of straw bale wall constructions. Overall, straw bale buildings show robust hygrothermal performance, when properly designed, and achieve very low energy use at a minimum of embodied emissions.

Structural characteristics of load bearing straw bale walls

Straw bales offer a renewable and affordable construction material suitable for a range of uses as both thermal insulation in walls and roofs, and for low rise loadbearing structural walls. As a co-product of food production, it places no further pressure on land use, and in common with other crop-based materials, straw captures and stores carbon dioxide through photosynthesis, offering the means to construct buildings with a net negative carbon emissions footprint. Straw also further reduces operational carbon emissions by virtue of its excellent thermal resistance. However, despite these benefits, and a successful construction history extending over 100 years in many countries worldwide, straw bale construction has still to make a major commercial impact in the wider construction market. Limited technical understanding of some fundamental performance characteristics (including structural capacity, hygrothermal behaviour, and durability), absence of technical standards, and a lack of certification and product warranty for straw bale, still remain barriers to wider acceptance. In this paper results are presented from a study on full-scale straw bale walls to evaluate the structural performance under vertical loading and lateral loading. The performance of identical straw bale walls, with and without plaster coats, is presented. The study is also unique in presenting on out-of-plane lateral loading and wall performance under eccentric vertical load cases. The research will support structural designers and enable wider uptake of this sustainable form of construction.

Research on Prediction Model for Durability of Straw Bale Walls in Warm (Humid) Continental Climate-A Case Study in Northeast China.

This research analyses straw degradation inside straw bale walls in the region and develops the prediction of degradation inside straw bale walls. The results show that the straw inside straw bale walls have no serious concerns of degradation in the high hygrothermal environment in the region with only moderate concerns of degradation in the area 2–3 cm deep behind the lime render. The onsite investigations indicate that the degradation isopleth model can only predict straw conditions behind the rendering layer, whereas the isothermal model fits the complete situation inside straw bale walls. This research develops the models for predicting straw degradation levels inside a straw bale building in a warm (humid) continental climate. The impact of this research will help the growth of low carbon energy efficient straw bale construction with confidence pertaining to its long-term durability characteristics both in the region and regions sharing similar climatic features globally.

Energy-Saving Potential of Applying Prefabricated Straw Bale Construction (PSBC) in Domestic Buildings in Northern China

The Prefabricated Straw Bale Construction (PSBC) has been proven as one of the most efficient construction methods to achieve low-energy buildings with low environmental impacts. This research presents analysis of the rationale for using straw bale constructions in northern China and a discussion of feasible constructions of PSBC to meet the local building codes following evaluations of potential energy performance of domestic buildings with PSBC in severe cold regions and cold regions in China. The results show that the buildings with PSBC reduce both heating and cooling energy uses, as well as heating intensities across the severe cold and cold regions, compared to the domestic buildings with conventional constructions. The findings of this research will contribute to reducing energy consumption in building industries in China.

Steady-state and dynamic hygrothermal performance of rendered straw bale walls

Wheat straw, in the form of compacted bales, is increasingly used as thermal insulation in the external walls of buildings. Common practice is to use a render finish, applied directly to surface of the straw bales, to protect them from decay, and enhance structural performance and fire resistance. Coatings are typically made of water vapour permeable materials, such as lime or earth-based renders. Such coatings should allow water vapour to diffuse through, minimising the risk of liquid moisture build up within the thickness of the wall, reducing likelihood of decay. However, to date there has been very limited scientific study of this behaviour in rendered straw bale walls. The aim of the work presented in this paper was to develop understanding of the hygrothermal performance of lime rendered wheat straw bales. A test panel was subjected to varying environmental conditions, including a thermal shock, dynamic freeze–thaw exposure and hot humid conditions. Key scientific contributions of this work include data on the dynamic and steady-state hygrothermal characteristics wheat straw bale walls, combined with the application of heat and moisture modelling. This work will further support uptake of straw bale construction by designers and their wider use in energy-efficient construction projects.

Energy Sustainability of Bio-Based Building Materials in the Cold and Severe Cold Regions of China—A Case Study of Residential Buildings

The aim of this research is to investigate the energy sustainability of cross-laminated timber (CLT) and straw residential buildings in the Cold and Severe Cold Regions of China. In the study, three building materials, namely reinforced concrete (RC), CLT, and straw bale, are used separately to design the building envelope in reference residential buildings in different climate zones. The energy consumption during the operation phase of these buildings is then simulated using Integrated Environmental Solutions—Virtual Environment software (IES-VE). The results show that both CLT and straw buildings are more efficient than reinforced concrete with a reduction in energy consumption during the operational phase. Overall, the calculated heating energy-saving ratios for CLT buildings in Hailar, Harbin, Urumchi, Lanzhou, and Beijing are 3.04%, 7.39%, 7.43%, 12.69%, and 13.41%, respectively, when compared with RC. The calculated energy-saving ratios for heating in straw buildings in comparison with RC in these cities are 8.04%, 22.09%, 22.17%, 33.02%, and 34.28%, respectively. The results also reveal that a south orientation of the main building facade results in approximately 5% to 7% energy reduction in comparison with east or west orientations, and as the building height increases, energy consumption decreases gradually. Although RC is the most frequently used building material in Cold and Severe Cold regions in China, as bio-based building materials, there is great potential to promote CLT and straw bale construction in view of the energy sustainability features.

Structural performance of non-plastered modular straw bale wall panels under transverse and gravity loads

Abstract Straw bale construction has a proven track record as a viable alternative for residential construction. Structural (load-bearing) straw bale panels typically consist of stacked straw bales and plaster skins. These systems exploit the structural capacity of the plaster/straw composite. The plaster is critical for providing structural strength and stiffness, as well as protection against pests, moisture, and fire. However, plastering bales is labour intensive and costly. A recent development has been dry bale wall (DBW) panels. These panels have a perimeter timber frame, recycled wood sheathing on both sides and straw bale infill. By eliminating the labour-intensive plastering of traditional straw-bale walls, DBW panels can be constructed rapidly and off-site in a sheltered environment, thus preventing exposure of the straw to moisture during construction. This paper describes the gravity and transverse load testing (based on ASTM E72 -15 [3] ) of DBW panels in-filled with wheat straw bales. To evaluate their strength capacity and failure modes is described. The out-of-plane flexural (OPF) tests exhibited a mean allowable bending moment of 1.80kNm with a factor of safety of 3. The axial compression (AC) tests exhibited a mean allowable line load of 22.8 kN/m with a factor of safety of 2.5. The local flexural header beam (HP) tests exhibited an allowable line load of 11.2 kN/m with a factor of safety of 3. The OPF and AC capacities of the DBW exceeded the Abbasi (2014)’s conventional structural insulated (STUD) wall. However, the DBW’s header beam strength and stiffness was inferior to Abbasi (2014)’s STUD wall.

Strawbale Construction – A Least Embodied Energy Material

Strawbale Construction – A Least Embodied Energy Material

“Experimental assessment of separation distances of a load-bearing straw-bale construction”

With an increasingly dense urban structure and wider use of energy efficient and combustible materials, the requirements on fire separation distances are becoming an actual topic. In the Czech Republic, separation distances are determined according to “fire openness” categorisation of external walls. In line with the Czech Fire Standards, combustible external walls must be considered as unprotected areas (fire opened areas) until the opposite is proven. This classification might be a crucial element in building design and for location of an object on a plot. This paper introduces a project on fire safety evaluation of a load-bearing straw-bale construction and focuses on experimental determination of fire openness of combustible external walls with incombustible surface (A1/A2 reaction to fire class). To assess fire risk and a contribution to fire growth and flame spread of the walls, a full-scale fire test of an experimental straw-bale house was carried out in September 2017. The experimental object was designed as a mock-up of a residential house, single-storey, stand-alone building with ground floor dimensions of 4.0 × 6.0 m and a height of 3.5 m with two symmetrical connected rooms. The observations and measurements showed that the experimental wall composition, even though it was not certified as a construction with a specific fire resistance, did not contribute to the fire propagation and could be assumed as a fire closed area, where as unprotected areas are considered only windows. In the case of the evaluated object, this classification leads to a reduction in separation distances of almost 4 meters. According to the results can be concluded that a different approach to evaluate fire openness could be desirable to establish.

Construction and monitoring of experimental straw bale building in northeast China

Straw bale buildings have the potential reduce the environmental impact of construction. Although the technique has been introduced into northern China more than a decade ago, the construction method and potential problems within straw bale walls have not been fully understood in existing research. Following an analysis of existing straw bale construction both in north China and worldwide, this paper proposes modifications to the straw bale construction details currently used in north China. The modifications involve in-fill raw material, toe-up design and lime render application. These modifications were incorporated into an experimental building constructed in north China, and after having been monitored for 12 months, the modified construction details were critically assessed. The data demonstrate that rice straw bale walls are resistant to agents of decay and offer reduced construction time and cost than standard wall construction in north China. The construction method has the potential to become a mature construction system in the Chinese market in the future offering significant benefits both in construction and operational cost and in environmental impact.

Time-dependent mechanical properties of straw bales for use in construction

Straw bale construction is a building technique with low environmental impact that has been gaining popularity over the last few decades. The aim of the paper is to contribute to the assessment of the potential of straw bales as a building material by measuring their dynamic mechanical properties and by modelling their response in time to mechanical load. To this end, relaxation tests, creep tests and tests with cyclic loads were performed on small prismatic straw bales at different loading levels. Data were fitted using different models: power models for cyclic load data and stretched exponential models for creep and relaxation data. Results show that bales exhibit a viscous-type response; the models used for data fitting predict that straw bales eventually settle to an asymptotic value of displacement in case of creep and of force in case of relaxation. Under cyclic loading, straw bales can dissipate energy; such capability, as well as the elastic performance of straw bales, decreases as cyclic loading continues, but can be retrieved after some time of resting from loading. A comparison between the creep performance of straw bales and that of conventional building materials showed that, in this respect, straw bales perform on average in a similar manner to masonry brickwork.

Straw bale construction in northern China – Analysis of existing practices and recommendations for future development

Straw bale buildings in China have been mainly limited to rural farm houses and self-builders. An expansion of straw-bale construction into main-stream medium-rise buildings has the potential to make a significant contribution to the reduction of both embodied and operational carbon in China as well as removing a major source of pollution. As a response, there has been the construction of straw bale buildings, however these buildings have several issues, resulting in the limited adoption of the technology.This paper makes recommendations for future straw bale design in northern China based on an inspection of existing buildings. The issues identified with existing construction details were subjected to computational simulation analysis which identified shortcomings in existing practice and proposes revisions to design detail in order to accommodate the environmental conditions in northern China. The paper provides a unique insight into current straw bale practice in northern China and proposes a practical and environmentally sound solution to the pollution crisis in this region.

A RESEARCH ON THE PERCEPTION OF ARCHITECTURE STUDENTS ABOUT STRAW-BALE BUILDINGS

Although straw-bale construction has been used for thousands of years, currently doesn‟t attract considerable attention by professional architects and students. The reason behind this is assumed to be the prejudices and lack of knowledge about straw-bale buildings. In the scope of this research understanding candidate architects point of view on the preference criterias that are effective about choice of straw-bale construction is aimed. For this purpose, among 214 students of private university (in Turkey) in 2015-2016 academic year, 100 students were selected through simple random sampling and the survey was conducted. The results show that according to the candidate architects, the properties such as its being compatible to nature, harmless to human health, recyclable and low-cost are the main positive qualities of straw-bale construction, whereas lifetime, structural properties and fire resistance are still calling into question. This study demonstrates that straw bale construction techniques, which have the potential to solve environmental problems, need to be given more attention in the architecture educational. Keywords: Straw-bale construction, preference criterias, architecture students

Analysis of the parameters affecting the mechanical behaviour of straw bales under compression

Straw bale construction is a building technique that has excellent thermal performance and limited impact on the environment. Improving knowledge of the mechanical properties of straw bales is important to understand the behaviour of straw bale buildings, especially in case of natural calamities, where straw bales may carry mechanical load and act as a “surviving cell”. The results of extensive tests conducted on bales of different materials are presented. The influence of the material, bale density, bale orientation, baling process and loading rate on the mechanical properties of straw bales was investigated. Force-displacement curves obtained from monotonic compression tests were analysed and relationships between the mechanical properties of straw bales and their geometry and density were determined. Continuous measurements of bales lateral displacement allowed Poisson's ratio to be calculated and, using a simple model, the strain to which bale strings are subjected during loading was estimated. Young's modulus was shown to mainly depend on the square of the density, while no influence of the loading rate and of strings pre-tension was observed. The Poisson's ratio did not remain constant during loading and it exhibited a different trend depending on the orientation of the bales. Moreover, it was observed that for flat bales a rearrangement of the straw fibres during loading occured and the maximum strings strain remained limited. Strings strain reached higher values for on-edge bales instead, and strings bursts occured more frequently.

Determining Moisture Levels in Straw Bale Construction

With the growing interest in sustainable building materials that are able to provide reductions in energy consumption, the viability of straw bale construction has recently been investigated, in particular, its resistance to moisture. The level of moisture that a construction is exposed to may have an adverse effect on its durability. Concerns are raised about the susceptibility of straw to decay when used as a walling system. It is an organic material, therefore is at risk of biodegradation under certain conditions. The research uses a range of measurement techniques to assess the effects of atmospheric conditions and wet render application on straw bale's moisture content, and it requires an understanding of the complexities of the transition of water vapor through the material and the interaction of moisture with the bale. Deviations in the moisture content within the straw bale caused by the second application of wet render were shown to be insignificant. Straw bale can withstand 25% moisture content for prolonged periods of time without degradation at temperatures not exceeding 10oC.