It was recently announced that the cost of retrofitting all the UK’s social housing to zero carbon levels would amount to over £100bn. 

That is a lot of money, and in the wake of Covid and Brexit is unlikely to be found; but there will be pressure to retrofit houses, and probably even more pressure to replace houses that do not meet the new targets. That will mean building more houses, and although it is rarely considered as such, building uses energy. 

Chefs will point out that you cannot make an omelette without breaking eggs, but architects rarely admit that you cannot build a zero-carbon house without spending a lot of energy, and developers never tell you that their development of a hundred ‘luxury’ one-bed apartments has come at the cost of losing either green fields or some substantial (and often re-useable) Victorian buildings. Even the most energy-efficient house will have to stand for some sixty years before it has saved the energy that has gone into building it. Passive houses often depend on substantial quantities of concrete, which is environmentally very damaging – some 8% of global CO2 comes from concrete production. 

If we built for long life, as our ancestors generally did, the energy employed to create our houses might be justified, but less than 10% of our housing stock in Northern Ireland is over a hundred years old. Many office blocks in Belfast city centre are demolished after little more than thirty years – long before they could demonstrate any energy saving. We can make a quicker and initially bigger impact on our building energy use by reducing new building than we can by attempting to improve every existing building. 

Energy saving is only one reason for re-using existing buildings. Every year 25m tonnes of UK construction waste goes to landfill. And that is to say nothing about the loss of habitat for birds, insects and plants every time a site is cleared and a new house occupies it. The mature gardens and hedges of an established street contain much more wildlife than a new housing estate does, as everyone who has been walking round their neighbourhood during lockdown will have observed. 

When we have to build new, let it be designed for a long life using minimal energy; but first of all, let us use what has already been built. It is too precious to waste.