Embodied carbon in heritage buildings: A counterintuitive case

Heritage buildings present a counterintuitive sustainability case. On first inspection, they appear to be inefficient by contemporary standards: solid wall construction, single glazing, and minimal insulation are all common features of pre-1918 building stock. The energy performance gap between a typical Berlin Altbau and a contemporary new build can be substantial.

Yet when the full lifecycle carbon footprint is calculated, heritage buildings frequently outperform new construction over realistic time horizons. The embodied carbon committed in existing fabric represents a carbon investment that has already been paid. To demolish and rebuild is to pay that cost again, plus the additional carbon emissions of demolition, disposal, and new construction.

• The embodied carbon of pre-1918 Gründerzeit housing stock is typically 250 to 400 kg CO2e per square metre of treated floor area, already committed
• New construction adds 500 to 800 kg CO2e per square metre on top, plus demolition emissions of approximately 50 to 100 kg CO2e per square metre
• The operational carbon penalty of retained heritage buildings can be reduced by 60 to 80 percent through internal retrofit, while preserving the entire embodied carbon investment

The retrofit approach

Heritage retrofit requires sensitive technical work, but the architectural answers are well established. Internal insulation, where appropriate to the construction; secondary glazing rather than replacement glazing where heritage glass is significant; high-efficiency heating systems replacing fossil fuel boilers; and careful detailing to avoid the moisture problems that have plagued some early retrofit work.

• Internal lime-based insulation systems maintain breathability and avoid the interstitial condensation problems associated with some impermeable insulation systems
• Secondary glazing preserves heritage glass while delivering U-values comparable to modern double glazing
• Air source heat pumps and high-efficiency electric heating are now compatible with the moderate operating temperatures suited to heritage fabric

"The carbon case for retrofit is now incontestable. The technical case is also clear. What remains is the cultural shift to treat heritage buildings as the climate asset they really are."