The building industry has a carbon problem, and most of it is not where people assume. Heating and cooling get the attention, but a substantial share of a building’s lifetime emissions is locked in before anyone moves in, embedded in the materials themselves.
Cement production alone accounts for a significant portion of global industrial carbon dioxide emissions. That single fact has pushed architects, engineers and material scientists to look somewhere unexpected for alternatives: at what builders used before Portland cement existed.
The chemistry that got forgotten
Lime was the primary binder in European construction for roughly two thousand years. It was abandoned within a few decades of Portland cement becoming commercially available, for reasons that were entirely practical.
Cement sets faster, reaches higher compressive strength and behaves more predictably. On a construction schedule, those advantages are decisive. Lime’s slower curing simply did not fit an industry moving toward speed.
What got lost in that transition was a set of properties that only became visible later, when cement based repairs on older buildings began failing in ways nobody had anticipated.
Carbonation: the part that changes the carbon maths
The most interesting property of lime is what happens after it is applied.
Limestone is heated to produce quicklime, releasing carbon dioxide. Quicklime is then combined with water to produce slaked lime, the material actually used in construction. Once applied, it slowly reabsorbs carbon dioxide from the air and converts back into calcium carbonate.
A significant share of the carbon released during production is reabsorbed over the material’s life. The cycle is not perfectly closed, since the kiln itself requires energy, but the net balance compares favourably with cement based systems where no reabsorption occurs.
This is not a marginal technical detail. It is the reason lime has re entered serious conversations about low carbon construction rather than remaining a heritage restoration niche.
Vapour permeability and why buildings got damp
The second property that drove lime’s return is permeability.
Traditional masonry was built to manage moisture by allowing it to move through walls and evaporate. When cement renders were applied to those walls during twentieth century renovations, that pathway closed. Moisture that could no longer escape through the surface migrated elsewhere, typically upward or laterally, causing damage above the treated area.
Building professionals encountered this repeatedly across Europe before the mechanism was widely understood. It is now a standard consideration in conservation work, and increasingly in new construction using breathable wall assemblies.
Beyond lime: the wider category
Lime is the most prominent example but not the only one.
Hempcrete, a mixture of hemp shiv and lime binder, has attracted attention because the plant sequesters carbon during growth. Its structural performance is limited, so it functions as insulation and infill rather than as a load bearing element.
Rammed earth has seen renewed interest in regions with suitable soils, offering high thermal mass and minimal processing energy.
Timber, particularly engineered mass timber, has moved furthest into mainstream commercial construction, with mid rise and increasingly tall buildings completed across Europe, North America and Australasia.
Pozzolanic additions, volcanic ash and similar reactive materials, improve lime’s strength and water resistance. The Romans understood this two millennia ago, and their marine structures remain intact today.
The honest limitations
None of this makes traditional materials universally superior, and pretending otherwise damages the argument.
Curing times are longer, which affects project schedules and financing costs. Skilled labour is scarcer, since the trades that once handled these materials have thinned considerably. Structural performance is lower, which constrains applications. Quality control is harder, because natural materials vary more than manufactured ones.
There is also a regulatory dimension. Building codes in most jurisdictions were written around industrial materials, and alternative systems often require additional testing and documentation to gain approval.
Where the shift is actually happening
Adoption is uneven and follows a logic worth noting.
The strongest uptake is in retrofit and conservation, where compatibility with existing fabric makes traditional materials the technically correct choice regardless of carbon considerations.
The second area is low rise residential, particularly in markets with strong environmental regulation or client demand.
Commercial construction has moved mainly on timber, where structural performance and fire testing have advanced enough to satisfy insurers and code officials.
Infrastructure remains almost entirely cement based, and will likely stay that way. The performance requirements do not admit alternatives at present.
What this means practically
For anyone specifying materials, the useful conclusion is not that cement should be avoided. It is that the default should be examined rather than assumed.
Many applications do not require the compressive strength cement delivers. Interior renders, non structural infill, restoration work and low rise masonry all fall into this category, and in each the alternatives perform adequately while carrying a substantially lower carbon burden.
The industry did not abandon lime because it stopped working. It abandoned lime because cement was faster. Whether that trade remains worth making is now a question with a different answer than it had a century ago.
