An extract on #thebaliguru
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 living space temperature. 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 then 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 are sparsely quoted. The thermal resistance of adobe is quoted as having an R-value of R0 = 0.41 h ft2 F/(Btu in) and a conductivity of 0.57 W/(m K) quoted from another source. A third source provides the following properties: conductivity=0.30 Btu/(h ft F); heat capacity=0.24 Btu/(lb F); density=106 lb/ft3 (1700 kg/m3). To determine the total R-value of a wall for example, multiply R0 by the thickness of the wall. From knowledge of the adobe density, heat capacity and a diffusivity value, the conductivity is found to be k = 0.20 Btu/(h ft F) or 0.35 W/(m K). The heat capacity is commonly quoted as cp = 0.20 Btu/(lb F) or 840 joules/(kg K). The density is 95 lb/ft3 or 1520 kg/m3. The thermal diffusivity is calculated to be 0.0105 ft2/h or 2.72x107 m2/s.