page_title: Adobe
section_title: Material properties
hierarchical_section_title: Adobe / Material properties
caption_attribution_description: English: Great Mud Mosque, Djenné, Mali Français&#160;: Djenné (Mali). La Grande Mosquée, construite en pisé.
context_page_description: Adobe is a building material made from earth and organic materials. Adobe is Spanish for mudbrick, but in some English-speaking regions of Spanish heritage the term is used to refer to any kind of earthen construction. Most adobe buildings are similar in appearance to cob and rammed earth buildings. Adobe is among the earliest building materials and is used throughout the world.
context_section_description: Adobe walls are load bearing, i.e. they carry their own weight into the foundation rather than by another structure, hence the adobe must have sufficient compressive strength. In the United States, most building codes call for a minimum compressive strength of 300 lbf/in² (2.07 newton/mm²) for the adobe block. Adobe construction should be designed so as to avoid lateral structural loads that would cause bending loads. The building codes require the building sustain a 1 g lateral acceleration earthquake load. Such an acceleration will cause lateral loads on the walls, resulting in shear and bending and inducing tensile stresses. To withstand such loads, the codes typically call for a tensile modulus of rupture strength of at least 50 lbf/in² (0.345 newton/mm²) for the finished block.
  In addition to being an inexpensive material with a small resource cost, adobe can serve as a significant heat reservoir due to the thermal properties inherent in the massive walls typical in adobe construction. In climates typified by hot days and cool nights, the high thermal mass of adobe mediates the high and low temperatures of the day, moderating the temperature of the living space. The massive walls require a large and relatively long input of heat from the sun (radiation) and from the surrounding air (convection) before they warm through to the interior. After the sun sets and the temperature drops, the warm wall will continue to transfer heat to the interior for several hours due to the time-lag effect. Thus, a well-planned adobe wall of the appropriate thickness is very effective at controlling inside temperature through the wide daily fluctuations typical of desert climates, a factor which has contributed to its longevity as a building material.
  Thermodynamic material properties have significant variation in the literature. Some experiments suggest that the standard consideration of conductivity is not adequate for this material, as its main thermodynamic property is inertia, and conclude that experimental tests should be performed over a longer period of time than usual - preferably with changing thermal jumps. There is an effective R-value for a north facing 10-in wall of R0=10 hr ft² °F/Btu, which corresponds to thermal conductivity k=10 in x 1 ft/12 in /R0=0.33 Btu/(hr ft °F) or 0.57 W/(m K) in agreement with the thermal conductivity reported from another source. To determine the total R-value of a wall, scale R₀ by the thickness of the wall in inches. The thermal resistance of adobe is also stated as an R-value for a 10-inch wall R₀=4.1 hr ft² °F/Btu. Another source provides the following properties: conductivity=0.30 Btu/(hr ft °F) or 0.52 W/(m K); specific heat capacity=0.24 Btu/(lb °F) or 1 kJ/(kg K) and density=106 lb/ft³ or 1700 kg/m³, giving heat capacity=25.4 Btu/(ft³ °F) or 1700 kJ/(m³ K). Using the average value of the thermal conductivity as k = 32 Btu/(hr ft °F) or 0.55 W/(m K), the thermal diffusivity is calculated to be 0.013 ft²/h or 3.3x10⁻⁷ m²/s.
caption: The Great Mosque of Djenné, Mali, is built in adobe. The struts projecting from the wall serve as decoration, as well as supports for scaffolding during maintenance.
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