A renewable building material is defined by its ability to naturally replenish on a human timescale, meaning the resource can be regrown or restored within a generation. Materials like timber, bamboo, or straw bales fit this description because they are biological resources with relatively short growth cycles. Bricks are not classified as a renewable resource because their primary components are geological in origin, having been formed over vast stretches of time. The core ingredients of traditional bricks are mined from the Earth, making them inherently finite materials with no natural regeneration process that can keep pace with human consumption.
The Finite Nature of Brick Raw Materials
The composition of a traditional fired brick relies on materials that are extracted directly from the Earth. Clay and shale, the main ingredients, are complex geological formations consisting primarily of silica (50–60%) and alumina (20–30%). These minerals are the product of slow geological weathering and sedimentation processes that take millions of years to occur. This means the supply is fixed and cannot be replenished once it has been quarried.
Obtaining these raw materials requires surface-level mining operations, often involving the extraction of clay from pits or the quarrying of shale. While clay is an abundant resource, extraction results in a permanent loss of that specific material from the local environment. This mining activity alters land use and can lead to habitat disruption. The consumption of clay and shale today represents a final use of a material that will not naturally reform for millennia.
Energy Consumption in Brick Production
A significant factor in the environmental profile of bricks is the substantial energy required to transform the raw materials into a finished building product. This energy used during manufacturing, transport, and construction is known as embodied energy. The production process for fired clay bricks is highly energy-intensive, with the most demanding step being the kiln-firing stage.
Bricks must be fired at high temperatures, typically ranging from 700°C to 1200°C, to achieve the necessary strength and durability through a process called vitrification. This thermal process fuses the clay particles together, requiring a large input of heat, which is often generated by burning fossil fuels like natural gas or coal. The energy consumed during the firing and drying stages alone can account for up to 87% of the total energy used in the manufacturing process.
The embodied energy of a typical fired clay brick is between 1.2 to 4.26 megajoules per kilogram (MJ/kg). This high energy demand results in a measurable embodied carbon footprint, estimated to be around 0.2 to 0.3 kilograms of carbon dioxide equivalent per kilogram of brick. The carbon emissions from powering the kilns represent a major environmental consequence associated with the production of new bricks.
Bricks in the Circular Economy
Despite using non-renewable raw materials and high manufacturing energy, bricks perform well in other sustainability metrics, particularly within a circular economy. The durability and longevity of fired bricks are a major advantage, as structures can last for 100 years or more, with many surviving for centuries. This long service life reduces the need for frequent replacement, avoiding the embodied energy and resource consumption of new construction materials over time.
When a brick building reaches the end of its life, the material can be recovered and utilized in two primary ways. The highest-value option is the direct reuse of intact bricks, which involves salvaging the units and cleaning them of old mortar. These reclaimed bricks are sought after for new construction and restoration projects, preserving the original embodied energy and eliminating the need for reprocessing.
The second end-of-life solution is recycling or downcycling the material into an aggregate. Bricks that are not structurally sound enough for direct reuse can be crushed into small particles. This crushed brick aggregate is then used as a substitute for virgin materials in applications such as road base, sub-base fill, or as a component in new concrete mixes. Although this process is considered downcycling because the material loses its original form, it diverts significant waste from landfills and reduces the demand for newly mined aggregates.