Arianne Shahvisi on the ills of construction (London Review of Books, 18 March)

The point at which we’ll have to reckon with rash, careless building is fast approaching. A recent paper in Nature noted that in 2020 the weight of human-made stuff exceeded living biomass for the first time. (It was just 3 per cent of biomass in 1900.) While trees and other vegetation weigh in at around 900 gigatonnes, buildings, roads and other infrastructure add up to 1100 gt (animals contribute 4 gt, half the weight of plastic on land and sea). There is now more concrete in the world than any other man-made material. After fossil fuels, it is the largest source of carbon dioxide, contributing 8 per cent of emissions, which puts it ahead of aviation and agriculture. Each of its ingredients has a calamitous footprint. Around 2 per cent of all water withdrawn from circulation is locked into concrete, contributing to aquifer stress and drought. Cement production involves intensive quarrying, dust pollution, high-heat kiln combustion and the release of carbon dioxide through calcination reactions. Then there’s sand, which is beginning to run out, triggering vast illegal networks around its extraction and trade. Desert sand is abundant, but its wind-sculpted grains are spherical; it’s the angularity of sea-eroded sand that makes the grains stack and bind so well (the ‘crackle’ that Vitruvius was talking about). Most land sources have been depleted; the dredging of beaches and riverbeds is wrecking marine ecosystems in many parts of the world.

Yet we need more homes. The government claims that its ‘green building revolution’ will hold new houses to higher standards of energy efficiency, leading to a reduction in emissions (improved insulation delivers a large share of that efficiency). They also boast of a six-year low in the numbers of rough sleepers, but this is down to the exceptional measures taken during the pandemic, and ignores the fact that deaths among homeless people rose by a third last year (more than a thousand people died on the streets in 2020). The government’s environmental claims focus too narrowly on the homes once inhabited – the ‘operational’ emissions – while neglecting the colossal ‘embodied’ emissions of the resources extracted and sunk into them. A badly built home may never make good the initial outlay in environmental terms, even if it does tick all the ‘green’ boxes. And there is the cost of all those vacant houses, embodied in bricks and mortar, but also represented by darkened windows, security guards, alarms and paid ‘guardians’: the expensive business of keeping houses empty when there are people who need them.