A cob house wall generally has a low R-value, estimated at R-0.22 per inch of cob thickness. For a thicker wall, this translates to approximately R-2.64 per foot of cob wall thickness.
Understanding Cob Wall R-Values
While the R-value of cob might appear low compared to conventional insulation materials, it's crucial to understand how cob structures manage temperature. The R-value measures a material's resistance to heat flow. For cob, the specific values are:
| Measurement | R-Value |
|---|---|
| Per Inch | R-0.22 |
| Per Foot | R-2.64 |
This means a 12-inch (1-foot) thick cob wall provides an R-value of about 2.64.
The Role of Thermal Mass in Cob Houses
Unlike conventional homes that rely heavily on high R-value insulation, cob houses leverage the principle of thermal mass. Thermal mass refers to a material's ability to absorb, store, and slowly release heat. Cob, being a dense earthen material, possesses excellent thermal mass properties.
- Heat Absorption: During hot days, the thick cob walls absorb heat from the sun and the warm air, preventing it from immediately entering the living space.
- Heat Release: As temperatures drop in the evening, the stored heat is slowly released back into the interior, keeping the house warm through the night.
- Temperature Stability: This process helps to regulate indoor temperatures, reducing drastic fluctuations and creating a more stable and comfortable environment year-round, often without significant reliance on mechanical heating or cooling systems.
Therefore, while the R-value of cob is modest, its inherent thermal mass capabilities contribute significantly to the comfort and energy efficiency of a cob house. Design elements like passive solar heating and strategic shading are often integrated to maximize these benefits.
