Adaptive reuse — converting buildings to uses other than their original purpose — is both more sustainable and often more interesting than demolition and new construction.
The embodied carbon in an existing building (energy used in original construction) is already spent. Demolition wastes it. Reuse retains it.
Beyond sustainability: old buildings have proportions, materials, and spatial qualities that modern construction rarely replicates. The market for loft apartments in converted warehouses, offices in converted factories — this is demand for spatial qualities that only come with age.