Pros and cons of using cob vs brick for thermal mass?

Building with Cob

Cob is a mixture of clay, sand, water, and sometimes straw that can be molded into various shapes for thermal mass construction. It has a higher thermal mass capacity compared to other natural materials due to its high clay content, making it suitable for storing heat from a rocket mass heater. A well-insulated cob wall with a thermal mass capacity of 300-400 kWh/m3 can store heat for several hours.

Durability and Maintenance

Brick, on the other hand, is more durable and requires less maintenance compared to cob. However, brick thermal mass requires a thermal mass capacity of at least 500 kWh/m3 to be effective. Brick can be more expensive to purchase and install, especially for a large-scale application. In contrast, cob is often free or low-cost, depending on the location and availability of materials. However, cob structures can be prone to weathering and erosion over time.

Comparison and Applications

When choosing between cob and brick for thermal mass, consider the size and complexity of the project. For small-scale off-grid applications, such as a single-family home or a cabin, cob can be a viable option due to its cost-effectiveness and eco-friendliness. However, for larger-scale applications or those requiring higher durability, brick may be a better choice. In both cases, proper insulation and design are crucial to achieve optimal thermal mass performance.