However, if we had to replace buildings once they reached sixty we would be in big trouble. Why?

For a start, our ability to recycle and re-use from demolished buildings means that we would be sending practically our entire building stock to landfill every sixty years. I shouldn’t really need to explain why I think this would be a bad idea.

Even in Japan, where traditionally homes were rebuilt by every generation, there are now serious Government moves to stop the practice. The Japanese authorities now believe that two-hundred years should become the new standard on how buildings should last.

Traditionally, buildings have been built to a nominal sixty-year design life using conventional building techniques. However, looking at Georgian buildings in Dublin, we see that with upgrades, refurbishment and a bit of ingenuity these buildings are operating at many multiples of a sixty year period.

So sixty years shouldn’t really represent what we really expect in terms of lifespan. But could we assume that the buildings we build today will be upright and useful in two-hundred years time? Honestly?

I suppose this might be a good time to say what I don’t mean. I don’t mean to restrict innovation, change or even say that buildings need to be built like nuclear bunkers and last forever.

However, I do think that in a time when there are so many agendas - such as the climate, sustainability, offsite construction - driving change through the industry, we should be really clear about how long buildings should be expected to last.

I’ll explain what I mean by means of an example. Some years ago, I was asked by a house designer what length of time he should design a house for.

I later found out that he was building on a floodplain and wanted to know how high to raise the ground floor level and still retain an acceptable level of risk of flooding. I explained to him that I thought that he might want to assess the length of time he thought that the house would be used and that this could be hundreds of years.

He was of the opinion that nobody would thank him for doing that (probably true) and that sixty years would be enough.

Whatever you think of the designer’s actions, he used an industry convenience – the sixty year design life. If he and his client (and perhaps planning authorities) were forced to sit down and rationally make decisions as to how long the building would be expected to function and design it accordingly, then it would not have occurred.

Being forced to think about the buildings functional lifespan might also mean that we would design buildings for much shorter life spans when appropriate, such as factories or superstores.

Why would we commit more resources to a building which we know it will be obsolete in twenty years?

We should be far more specific about how long we expect our buildings to remain functional or else we might just get the default sixty years.

This article was written exclusively for irishconstruction.com by Éanna Nolan, head of BRE Ireland.