While I am supportive of measures architects could take to achieve a zero-carbon built environment, I was confused by the mixed messages in Piers Taylor’s comments calling for reducing the use of concrete by three quarters. He correctly notes concrete has a lower CO2 footprint than most other building materials, but ignores the fact that wood used in construction (particularly for mass timber designed structures) also has a high carbon footprint. While innovative changes are indeed being made in the industry that lower the CO2 content of cement used in concrete, limiting concrete to “essential aspects” of construction (i.e. anything lasting 200 years) and using far more timber is illogical and unrealistic. All tall timber buildings in reality are hybrid structures that require concrete or steel for structural support and safety. And it is unrealistic to think that high-density cities of the future can be built with more timber harvested from already over-stressed forests in lieu of concrete.