By Jan Dolezal
In many discussions and articles, “sustainable cities” and “vertical cities” are used almost as synonyms and many imply that floor-space-ratio correlates with sustainability. In this post I present arguments to challenge this popular belief.
Look at China for example. Shanghai Tower – the world’s second tallest building under construction boasts to be “sustainable best practice” and Broader Group’s Sky City which would become world’s tallest building is all intended as a role model of replicable sustainability.
Yes, there are clear energy efficiency advantages of going vertical. Less surface area per usable floor space results in less heat loss and less material required for enclosure. Large scale HVAC systems are more efficient. High density reduces the need for transportation.
But there are also numerous disadvantages to offset the gains. Bottom floors need to carry the full weight of all the upper floors, resulting in significantly more materials for primary structural systems. High buildings require extensive foundations to achieve stability in high winds and earthquakes, which drives material requirements further up. Less surface per floor space may result in less natural light. Smaller roof area versus equivalent horizontal buildings provides fewer opportunities for solar installations. Smaller parcel area does not provide opportunity for geothermal heating and cooling, which can sustainably reduce energy demands of a family house by 40-70% with ~10 year payback. Vertical transportation also requires additional materials to build and energy to operate. Given all these drawbacks the real resource efficiency advantage of vertical construction is at best questionable.
Sustainability is however not only about resource efficiency. Vertical construction poses other environmental challenges. One is visual contamination of high-rise buildings which prompted some place such as Hawaii, Washington DC or Canary Islands to impose limits on height of buildings. Increased stress on soil leads to sinking of many dense centers (e.g., Manhattan) that can hardly be called sustainable.
We can question sustainability of vertical construction even under current conditions, but what if conditions change? Is it really robust? We now live in time of relative peace, but how sustainable is vertical construction in times of war? Super tall buildings are most vulnerable and an easy target as we have already seen in the case of 9/11. Even if enemy does not destroy the whole building, how safe is it in case of a big fire? What if for any reason the electricity grid fails and people are stuck on 200th floor? If generators run out of fuel, how do we pump water to that height? Can you imagine the social unrest if for any reason (war, natural disaster…) supplies for such a building are interrupted? Horizontally distributed city of well insulated single family homes that have own geothermal heating, solar system, can revert to using wood in a fireplace and grab some food in own garden seem like a way more robust sustainable solution.
I don’t want to suggest that everyone lives on a self-sustaining farm, but I protest against implying correlation between verticality and sustainability. Perhaps the optimal solution is somewhere in between, such as 8-story modular buildings?
Image source: http://www.tdrinc.com/images/photos/large/Towers04a1.jpg