Why clay bricks can have a lower carbon footprint than alternative masonry units — a comprehensive, evidence-based article

When evaluated sensibly — using whole-building functional units (area of wall or thermal/structural function) and life-cycle boundaries — clay bricks often produce less net carbon over a building’s life than many alternatives (especially cement-rich concrete blocks and some lightweight manufactured blocks). The reasons are threefold: (1) clay bricks’ embodied carbon is concentrated in firing (which is addressable with efficiency and fuel changes), (2) many alternatives rely heavily on Portland cement (very carbon-intensive), and (3) clay bricks provide thermal mass and longevity that reduce operational energy over decades. The net result: under typical South African conditions and when local production and whole-life impacts are considered, clay masonry frequently performs as well or better on CO₂e than alternatives. Clay Brick+2ResearchSpace+2

1. How we should compare materials (the right frame)

To avoid apples-vs-oranges mistakes, comparisons must use:

• The same functional unit — e.g., 1 m² of external wall delivering the same structural and thermal function, or whole-building cradle-to-grave impacts (50-year life is common).

• Life-cycle boundaries — cradle-to-gate (production only) misses operational savings from thermal mass; cradle-to-grave (or whole-building LCA) captures both embodied and operational emissions.

• Local context — grid carbon intensity, transport distances, dominant fuel types for firing, and construction practices all change outcomes. The Clay Brick Association (CBA) and University of Pretoria work recommend whole-building LCA comparisons for South Africa. Clay Brick+1

2. The basic emissions profile: clay bricks vs cement-rich alternatives

• Clay bricks (fired): the lion’s share of embodied CO₂ is from kiln fuel used to fire bricks; industry LCAs in South Africa report typical production-phase intensities around ~0.27 kg CO₂-e/kg (cradle-to-gate) as an industry average (formal sector). This means energy/fuel choices and kiln efficiency dominate the footprint. Clay Brick

• Concrete blocks / concrete masonry units (CMUs): their embodied carbon is heavily influenced by cement content. Portland cement/clinker production is extremely carbon intensive (often ~0.7–0.9 kg CO₂ per kg of cement depending on technology and calcination share). Even when concrete blocks use aggregates (which lower embodied carbon per kg), the cement fraction drives a large share of their emissions. CSIR and other studies note concrete blocks’ impacts are primarily cement-driven. ResearchSpace+1

• Autoclaved aerated concrete (AAC) and lightweight blocks: AAC can be lighter and give structural/insulation advantages (reducing dead load, steel/concrete for structure), but some LCAs and comparative studies show that per kg or even per m³ AAC may have similar or higher impacts depending on manufacturing energy, autoclaving process, and raw materials — and the end result depends on how much material is needed to perform the same function. Several recent studies find AAC’s environmental advantage is not automatic and depends on functional comparison. MDPI+1

3. Why clay bricks often come out ahead on a fair, functional basis

A. Thermal mass reduces operational (use-phase) emissions

Clay brick walls have high thermal mass: they store and delay heat flow, smoothing indoor temperature swings and lowering heating/cooling energy in many climates. Whole-building LCA and thermal performance studies in South Africa show brick walls can reduce operational energy needs — and when those savings are modelled over a 50-year life the operational savings can offset a substantial portion of the production emissions. Thus, on a cradle-to-grave basis clay masonry often achieves lower net CO₂ than lighter, low-mass walls that require more heating/cooling. IRBNet+1

B. Cement (not aggregate) is the big carbon driver in concrete blocks

Concrete and cement-rich blocks derive a large share of embodied CO₂ from clinker/cement manufacture (calcination + fuel combustion). Because clay bricks’ production emissions are concentrated in thermal energy (which can be improved or decarbonised) and because cement’s process emissions are intrinsic to its chemistry, reducing emissions in clay brick production is often more tractable (fuel switching, heat recovery, kiln efficiency) than eliminating the chemical CO₂ inherent in cement. Comparative analyses highlight cement’s central role in concrete block impacts. ResearchSpace+1

C. Durability, reuse and lower maintenance

Clay bricks are durable, resistant to weathering and often reusable (reclaimed face bricks). Reuse removes the need for new manufacture for replacements and can reduce lifecycle emissions. Recycling pathways for concrete and AAC exist, but reclaimed face bricks have a strong market value in many contexts, improving the lifecycle outcome for clay masonry. The SA CBA LCA notes reuse and long service life as important whole-life advantages. Clay Brick

D. Local manufacturing and transport sensitivity

If clay bricks are produced locally and distributed regionally, transport emissions are lower than heavy imports or long-haul concrete products. Many countries (including the UK example) show imported bricks have much higher CO₂ footprints due to shipping — a reminder that local sourcing matters. The Guardian+1

4. Where alternatives can win (and why we must remain nuanced)

Clay bricks do not always outperform every alternative in every metric. Situations where alternatives may be lower-carbon:

• Structural optimisation: AAC and some lightweight blocks can lower the total material demand (smaller structural section sizes, less steel/concrete in the framing), which can reduce whole-building embodied carbon on multi-storey projects — but this depends on the building design and must be modelled at the building level. MDPI

• If clay bricks are fired with high-carbon coal and alternatives are manufactured using low-carbon electricity or low-carbon cement substitutes, an alternative may have lower production emissions. Local energy mix and fuel sourcing matter a lot. Clay Brick+1

• Innovations in cement (e.g., LC3, partial clinker replacement) and increases in low-carbon cement production can reduce the concrete block penalty over time. But currently, cement is chemically constrained and still a large emissions source. ACS Publications

The upshot: you must compare whole-building cradle-to-grave impacts for the same functional performance (insulation, strength, fire protection, floor area) to be certain which material is best for a given project.

5. Evidence highlights (key references for the most important claims)

1. South African industry LCA for clay bricks (CBA) — provides production (cradle-to-gate) intensities and notes the dominance of firing energy and the importance of whole-building comparisons. This is the core source for SA figures. Clay Brick

2. University of Pretoria / Van Rooyen & Vosloo thermal performance studies — show how wall type and thermal mass affect operational energy in South African climates; supports the thermal mass argument. IRBNet

3. CSIR / comparative embodied energy work — explains that concrete blocks’ embodied emissions are dominated by cement content and that manufacturing choices strongly influence outcomes. ResearchSpace

4. Recent LCA literature reviews — e.g., MDPI review of EPDs and studies of masonry products — show variability across products and the need for functional comparisons; some studies find AAC has higher impacts per mass but may perform differently per functional unit. MDPI+1

5. Comparative and regional studies — multiple peer-reviewed studies (and regional LCA work) conclude that clay bricks’ production emissions are solvable via energy efficiency and fuel switching, whereas cement’s process emissions are more fundamental — underpinning the argument for clay bricks’ relative advantage under many realistic scenarios. ScienceDirect+1

6. Practical implications — what builders, specifiers and manufacturers should do

For architects / specifiers:

• Request whole-building LCAs (cradle-to-grave) or at least compare per-m² wall functional units rather than per-kg numbers.

• Value thermal mass where it reduces operational energy (hot daytime/cool night climates benefit most). IRBNet

For manufacturers (clay bricks):

• Prioritise fuel switching (away from coal), kiln insulation, and heat recovery — the highest leverage interventions for lowering production CO₂. Document energy and emissions transparently (EPDs). Clay Brick+1

For those considering alternatives:

• Model total building impacts (material savings vs increased operational energy). Don’t assume AAC/concrete blocks are automatically lower-carbon without that modelling. MDPI

7. Bottom line / conclusion

• Clay bricks can and often do have a lower life-cycle carbon footprint than many alternative masonry units when evaluated on a like-for-like functional basis in South Africa. The main reasons are (a) the potential to reduce or decarbonise the firing energy that dominates clay bricks’ production emissions, (b) the intrinsic high carbon intensity of cement used in many concrete blocks, and (c) clay bricks’ thermal mass and durability, which lower operational emissions over decades. Clay Brick+2ResearchSpace+2

• That said, outcomes are context dependent — local fuel mixes, transport distances, manufacturing technology, building design, and advances in low-carbon cement are all important. The responsible professional practice is to always compare whole-building LCA results for the specific project and locations under consideration. MDPI+1