The greenest building is almost always the one already standing. Every structure that comes down takes with it the energy that went into making it — the cement, the steel, the years of curing — and every replacement starts that bill again from zero.
Renewal is harder than demolition, and that is the whole difficulty. A retrofit has to be surveyed rather than assumed: what the frame will still carry, where the water has been getting in, which walls are doing work nobody drew. Only then can anyone say honestly what it will cost.
What comes back is worth the trouble. Older buildings were planned around light and air because they had to be, and their proportions are frequently better than what a spreadsheet would put up today. Keeping them keeps a street legible.
Our rule is simple enough to state and slow to apply: replace what has failed, repair what has not, and leave the parts that were right to begin with alone.
The greenest building is almost always the one already standing.
