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Mud brick has been the predominant construction material throughout history in the hot and arid region of Iran for thousands of years.

This material possesses various environment-friendly characteristics. regarding its formation and accessibility, extraction, transport, construction technologies, low emission, maintenance, durability, reusability etc. However, the operation of traditional adobe construction to withstand earthquakes has always been a controversial issue for designers due to its low resistant against seismic hazards.

One key to the safety of adobe buildings against earthquake is an additional building material with good tensile resistance that can create good post-and-beam structure in combination with adobe.

This article investigates three possible building materials for this purpose: timber, steel and concrete to find out which is the most sustainable building material for framing of adobe buildings in this region.

The study is made by application of qualitative method to provide insights into the research question by gaining an understanding of the underlying factors that make each of these three materials be environmentally sustainable or not.

These building materials are compared regarding their degree of environmental sustainability as Well as locality and abundance in the area.

For the first item; timber, steel and concrete are compared in three different phases: pre-construction, construction and post-construction, to find out their degree of sustainability as a building material in the region. The results show that timber owns the most sustainable features, steel on the second place, and concrete is the most unsustainable material amongst The three.

The following part investigates accessibility of timber and steel in the area to define the most sustainable building material in the region.

FAO assessments for forest resource condition are reviewed to assess the accessibility of timber as a building material in hot and arid region of Iran, where suffers from lack of forests. The results demonstrate that Iran's central and-northern forests in their present situation cannot supply the required wood for construction in Yazd. However the present programs for revitalization of the deforested lands can provide the required wood for construction in near future.

Meanwhile the present capacity of steel industry in the area and the existing infrastructure. for production of steel as a building material around Yazd is studied. The extensive development of steel industry in Iran during the past fifty years has established a good infrastructure that can produce sufficient steel regarding the considerable resources of iron ore and steel crude in the area.

This paper finally proposes, for short term; steel as the binding material for improvement of tensile resistance in adobe construction in Yazd. Timber is however the most environmentally sustainable material to be applied after the improvement of the forests in the country in near future.