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Earthen building materials offer an environmentally sustainable alternative to conventional materials because they are locally available, minimally processed, and waste-free. However, they have not been comprehensively implemented because their technical data is highly variable, and they are not fully represented in building codes. To address these hurdles, this paper presents an environmental assessment and a policy repair review, including an environmental embodied impact analysis, and a discussion of the regulatory development required for earthen construction. The results of the environmental assessment show that earthen wall assemblies significantly reduce environmental impacts by 62-99% when compared with conventional assemblies such as timber frame and concrete blocks. Additionally, the policy discussion provides recommendations to overcoming materials variability and regulatory organizational collaboration. Overall, this paper highlights the importance of environmental and policy measures that could be used by policy makers and earthen building advocates in their endeavours to catalyse the representation of earthen building materials and methods in mainstream construction. 1. A brief history of unsustainable architecture Throughout history, human building practices followed the path of building shelters out of locally abundant materials, where the building components were always mined and curated from the nearby environment: earth, stone, trees and grasses. The evolution of these various shelters was developed in different cultures by improving materials, energy, water, and waste solutions, adjusting from generation to generation to meet new needs and opportunities [1,2]. It is only in the last few centuries that our relationship with buildings has changed. Cementitious materials started playing a vital role in the ancient world: the Egyptians obtained cementitious material by burning gypsum; the Greeks used lime by heating limestone; and the Romans developed hydraulic cement by adding crushed volcanic ash to the lime [3]. These techniques were re-developed and patented in western Europe as “Roman Cement” (in 1794) and “Portland Cement” (in 1824) [2,4]. These last developments, accompanied by the industrial revolution, changed the way building materials were produced and the techniques used for construction. Started as a wave in Western Europe, these highly-processed building materials and methods are still spreading into less-developed parts over the world. Thousands of new building products have been developed and replaced local traditional materials in ways that minimize labor and allow an increase in the pace and amount of construction. 1 School of Architecture, Carnegie Mellon University, Pittsburgh, PA 15217, USA 2 Department of Civil and Environmental Engineering, University of Pittsburgh, Pitt, PA 15260, USA  Corresponding author. E-mail: rbenalon@andrew.cmu.edu Nevertheless, these modern building practices require the extraction, transportation, and heavy processing of (often toxic) building products in ways that contribute to the consumption of large amounts of non-renewable resources, contributing to the deterioration of our global environmental [5]. In terms of building materials standardization, conventional modern construction materials, mostly made of steel reinforced concrete, wood, and synthetic insulation, are being implemented in the majority of modern buildings while meeting a wide variety of building codes and standards. Therefore, in light of the environmental impacts specified above, these building codes and standards (that were initially developed to ensure individual safety and public general welfare) are currently neglecting larger, ecologically-based risks to natural systems upon which everyone’s safety and health ultimately depend [6]. Nonetheless, due to an increased interest in sustainable and green building practices, additional nonmandatory regulatory and rating systems have been developed that support materials and resources considerations in projects, as shown by the growing numbers of L.E.E.D certified projects [7,8]. 2. Why earth? The case for earthen building materials and methods Parallel to the interest in sustainable and green building practices, there has been a growing interest in ecological and natural building materials and methods [8]. These are defined as minimally processed and locally available materials that enhance their local environment and economy, rather than only mitigating negative impacts [9]. Examples of natural building materials include natural fibers like straw and hemp, and earthen materials like sand and clay. Specifically, earthen materials exhibit various advantages; they provide high thermal inertia and offer better structural capacity in compression. As opposed to trees and crops, earth is usually abundant in and around the construction site. As opposed to cellulose-based materials, it has better resistance to fungi, insects and rodents. Furthermore, it allows a diversity of forms and styles, from sculptural monolithic assemblies to modular components [11]. Earthen architecture can be defined as building materials and methods in which clay is used as a binder [10]. It is also often referred to as a traditional and/or vernacular building material and method [12]. However, some earthen building techniques were developed in the past few decades (e.g., compressed earth blocks), while others were used traditionally and currently receive a new architectural interpretation (e.g., rammed earth) [13,14]. More specifically, in recent decades, material science has come to know much more about how clay works as a natural binder in building materials. Therefore, earthen building materials are recently suggested to provide a natural concrete alternative, namely a lowcarbon, clay-based concrete [10]. Despite their benefits, earthen building materials and methods remain mostly unrealized in the mainstream construction industry from various reasons. First, the literature lacks aggregation of technical data that could quantify the performance of earthen materials for different climate and seismic conditions [15,16]. Second, there is a broad and often mistaken perception of these materials as being low-tech and having poor overall performance [8,17]. Lastly, one of the main barriers that is especially evident in the case of cob and earthbags is the lack of complete and user-friendly codes and regulations that could give rise to the conventional implementation of, for instance, affordable homes [6,18]. These concerns are broadly echoed in the literature. Woolley (2006) concludes that public policy incentives, particularly formal codes and regulations, should be developed for earthen materials, accompanied with financial incentives, in order to give rise to real-estate investments. Similarly, Swan, Rteil, and Lovegrove (2011) suggest that future research should a) aggregate the existing experimental engineering studies; b) provide analytical and numerical insights that could facilitate the design process and allow the inclusion of earthen materials in building codes; and c) provide a life cycle analysis of earthen construction assemblies. 3. Performance-based assessment of earthen building materials vs. conventional assemblies The performance of a building material describes its functioning in terms of declared characteristic properties. Depicted though levels, classes or short descriptions, these performance parameters can portray the main features of earthen materials as opposed to conventional assemblies. Table 2. Technical performance of earthen materials as opposed to conventional materials Performance Parameter Earthen Building Materials Timber Frame [19] Concrete Masonry [20] uninsulated (insulated) Cob Rammed Earth Light Straw Clay T h er m al Thermal Resistance (mK/W per inch) 0.051 [21] to 0.106 [22] 0.025 [21,23] to 0.06 [24] 0.14 [25] to 0.26 [26] 0.5-0.7 (with fiberglass batt) 0.05 (0.15) [27] Thermal capacity (kJ/mK) 1655 [28] 1830 [29] 400 [26] 10 [26] (25) [30] 170-380, depending

Integrating Earthen Building Materials and Methods into Mainstream Construction Using Environmental Performance Assessment and Building Policy