Our modern buildings

[George.]

won't last as long as these:

[George.]

Reason: they are mostly reinforced with metal. As anyone who has ever cared for a boat knows, all metal corrodes eventually.

Over the past 80 years or so we have built new housing for most of the world's population, mostly using rebar. How long will our buildings last, I wonder? Will there be a period in the future when rich countries have to demolish and rebuild their cities wholesale, while in poor countries thousands die every year as old buildings crumble?

[ron ll]

In a recent documentary on rebuilding Notre Dame, it was discovered that some stone courses had been held together with iron staples.

As to your point, as a now retired architect, I’ve had the dubious pleasure of seeing a couple of commercial buildings that I designed, be demolished to make room for newer structures as the real estate became more valuable. I try to tell myself it was nothing personal.

[WszystekPoTrochu]

Buildings tend to protect rebar from rusting, even if for the simple reason of its inhabitants not being keen on being exposed to elements.

Bridges and alike, however...

[birlinn]

In a recent documentary on rebuilding Notre Dame, it was discovered that some stone courses had been held together with iron staples.

As to your point, as a now retired architect, I’ve had the dubious pleasure of seeing a couple of commercial buildings that I designed, be demolished to make room for newer structures as the real estate became more valuable. I try to tell myself it was nothing personal.

Only two?
My list is longer.
But two of the survivors are now listed buildings, so might outlast me.

[ron ll]

Only two?
My list is longer.
But two of the survivors are now listed buildings, so might outlast me.

I was being modest. Probably more than two no longer exist.

[George Jung]

We build now for needed replacement, don't ya think? 'It's good business'.

Facades, vs stone construction.

[Rapelapente]

This roman bridge

Roman_Bridge,_Vaison-la-Romaine,_France._Pic_01.jpg

Survived to this in 1992...



Cars are still rolling over.

[Breakaway]

We also may have gleaned societal knowledge that nothing lasts forever and so began building accordingly.


Kevin

[Figment]

The Pantheon has vastly outlived most of it's contemporaries, perhaps unreasonable to uphold the exception as the benchmark.

[Gerarddm]

Iron swells as it rusts. Way bad for massive inclusion in stone structures.

[George.]

The Pantheon has vastly outlived most of it's contemporaries, perhaps unreasonable to uphold the exception as the benchmark.

How about something 1400 years older?

[J P]

For almost forty years, timber framing has been my living. One thing about using heavy timber is that when the buildings, bridges, whatever, have reached the end of their usefulness, the timbers will probably be salvaged and repurposed while most of the rest of the building materials will get smashed up and land-filled.

We often use reclaimed timbers, some might be a couple hundred years old or more, that show evidence of having been used in more than one structure. In fact, I just made some parts for a shave horse out of a piece from an old oak barn timber. That timber had evidence of having been used in two different applications before we put it to use in a third. My shave horse gives it yet a fourth use.

[LeeG]

Do you really want a 2200 sq ft four bedroom five bath suburban house to last 2000 yrs?

[Mrleft88]

There are structural cementicious (Or however it's spelled) building materials that are lighter weight, stronger, and less corrosive than what is mostly used today. The thing is USG and the other big concrete companies don't own the patents to them. Some say that the pyramids of Giza aren't built of stone, but rather a very strong form of concrete.

[Peerie Maa]

For almost forty years, timber framing has been my living. One thing about using heavy timber is that when the buildings, bridges, whatever, have reached the end of their usefulness, the timbers will probably be salvaged and repurposed while most of the rest of the building materials will get smashed up and land-filled.

We crush it and reuse it.

Crushed rubble is a recycled aggregate made from waste materials from construction and demolition projects. It’s available crushed up to 80mm. Suitable as a subbase, this multifunctional material is typically used in large road construction, for driveways, patios and for land-filling tasks such as laying foundations for new homes or extending existing properties. Crushed rubble is eco-friendly and has a relatively long lifespan.

Crushed Concrete Type 1

The material is graded 40mm with reduced fines in accordance with the specification for Highway Works 803 (SHW 803).
Crushed Concrete Type 1 makes a cheap alternative to MOT Type 1.
Uses

Crushed Concrete Type 1 is a standard sub base material for roads but can be used for a wide range of other applications including drives, tracks, paths, trench fill, backfill, capping layers, oversite fills and foundations. Crushed Concrete Type 1 can also be used as a general purpose hardcore.

Mind you, from what I read on here you lot don't built roads, you just let them wear out

[George.]

Still wondering how long the average concrete and rebar building from say, the 1960s, will last before it crumbles or has to be condemned.

[Peerie Maa]

Thius concrete viaduct was built in 1901.

I doubt that rebar was required.
This from 1889 used twisted steel rebar.

[George.]

The first one, without rebar, would be the same technique as the Romans, basically.

The second one doesn't look as challenging structurally as the first one, or as a modern 10-story apartment block.

[Peerie Maa]

The first one, without rebar, would be the same technique as the Romans, basically.

The second one doesn't look as challenging structurally as the first one, or as a modern 10-story apartment block.

It is a very flat arch, which is structurally challenging.
However, you were asking

how long the average concrete and rebar building from say, the 1960s, will last before it crumbles

so the evidence suggests that it could be in excess of 133 years.

[heimlaga]

Likely not that long.
The surface of modern concrete continously takes up carbon dioxide from the atmosphere converting itself to limestone starting from the surface. Limestone has smaller volume that concrete so hairline cracks develop and they go as deep as the carbonatisation has reached. On typical 1960-ies concrete buildings this carbonatination has by now reached the depth of the rebar (between 3 and 5 cm typically) and as the PH in the surrounding material changes to that of limestone and hairline cracks lets in oxygen the rebar starts to rust. As rust has a greater volume that it's constituent iron it breaks the cracked limestone asunder and the concrete crumbles.

Exterior concrete (for instance concrete facades) from the 1960-ies is now pretty much at the end of it's technical lifetime and will be falling down in the coming decades. Indoors in dry conditions carbonatisation is slower and rebar less prone to rust so the typical concrete slabs in brick building from the 1950-ies and very early 60-ies probably still have a hundred years or so to go before the concrete crumbles.

[George.]

So in a hundred years or so everything will have to be rebuilt.

But nature works in waves, not spikes. Let's say the half-life of the average concrete building is 133 years. Half the buildings will fail before then. In the preceding decades there will be crumbling buildings everywhere. Especially in rainy poor countries.

[WszystekPoTrochu]

The second one doesn't look as challenging structurally as the first one, or as a modern 10-story apartment block.

An arch so spread is mostly an aesthetic choice, it won't provide much support

As for durability: This pedestrian bridge, exposed to brutal weather, was built in 1984
This factory from 1912, with concrete clearly exposed to the elements, is nowhere near crumbling

This overpass from 1975 got demolished in 2015, after 40 years of literally no maintenance. It had bad luck of requiring maintenance when history made a leap forward, and then repairing it got as expensive as rebuilding. So they waited another decade, again with little to no maintenance, and then rebuilt. But you know what? Almost every material, be it stone, brick or concrete, requires maintenance. Properly maintained building will last for centuries. Like this beautiful collegiate from the 1100s, or this nice classic wooden church from the 1300s, reusing 1100s foundation of its predecessor. Modern ones won't fare worse. It's fairly easy to find still inhabited homes built during the middle ages, despite them being clearly undersized for today's standards. Or, in some cases, being undersized and awfully crooked. I see no reason to think that our reinforced concrete homes, if maintained, will last shorter than brick and wood structures from centuries ago.

[phiil]

won't last as long as these:

They were also modern when they were built.

[heimlaga]

An arch so spread is mostly an aesthetic choice, it won't provide much support

As for durability: This pedestrian bridge, exposed to brutal weather, was built in 1984
This factory from 1912, with concrete clearly exposed to the elements, is nowhere near crumbling

This overpass from 1975 got demolished in 2015, after 40 years of literally no maintenance. It had bad luck of requiring maintenance when history made a leap forward, and then repairing it got as expensive as rebuilding. So they waited another decade, again with little to no maintenance, and then rebuilt. But you know what? Almost every material, be it stone, brick or concrete, requires maintenance. Properly maintained building will last for centuries. Like this beautiful collegiate from the 1100s, or this nice classic wooden church from the 1300s, reusing 1100s foundation of its predecessor. Modern ones won't fare worse. It's fairly easy to find still inhabited homes built during the middle ages, despite them being clearly undersized for today's standards. Or, in some cases, being undersized and awfully crooked. I see no reason to think that our reinforced concrete homes, if maintained, will last shorter than brick and wood structures from centuries ago.

The difference being that brick does hardly change with age. Neither does lime mortar once it has set. Wood looses it's sap content and becomes a bit brittle and more prone to suck up water as centuries go by but in a soundly designed building that will not matter much. The famous Roman concrete is chemically very different from modern concrete and once set it doesn't change much.

We once restored a log building which was originally built in the 1690-ies and around 80% of the damaged timber which we shifted was damaged only because of a severe roof leak in recent times and around 10% because of a careless remodel in the 1880-ies. Only around 10% of the timber we shifted was past it's natural technical lifetime.
A long lasting building of any material must be built in such a way that every single past of it can be shifted out when that particular part has reached the end of it's lifetime or been damaged by a spell of recklessness.

[George.]

A long lasting building of any material must be built in such a way that every single past of it can be shifted out when that particular part has reached the end of it's lifetime or been damaged by a spell of recklessness.

Just like a wooden boat.

[George.]

As for durability: This pedestrian bridge, exposed to brutal weather, was built in 1984
This factory from 1912, with concrete clearly exposed to the elements, is nowhere near crumbling

Yes, but then you have buildings like the one that crumbled in Florida, or the ones that crumble rather often in places like Rio or Bangladesh.

I am not thinking of individual buildings, let alone the best of the bunch. I am thinking about the average building, which is not so well made. Or rather, about the millions of below-average buildings, which will crumble before the half-life of the average building.

[The Q]

Thius concrete viaduct was built in 1901.

I doubt that rebar was required.
This from 1889 used twisted steel rebar.

Glennfinnan viaduct was indeed built of poured mass concrete without rebar, by Robert McAlpine, it was built hollow with rubble infill.
The nearby Loch Nan Uamh viaduct, has a horse and cart inside, it reversed back to tip rubble in and went to far, falling inside . There was no point in recovering it so it got buried in further rubble.

[WszystekPoTrochu]

I am thinking about the average building

The average building over a 1000 years old looks like this:
get-108.jpg
(almost contemporary to Pantheon, found here)

or like this:
biskupin.jpg
(7th century BC, found here)
at best, and after some extra careful maintenance.

[TomF]

A friend is a civil engineer who runs a business specializing in the preservation and restoration of centuries' old buildings. On the one hand, he's skeptical of the durability of building methodologies and materials with less than 150 years of track record, because by definition we don't have examples of such structures standing up for centuries.

On the other hand, he said that the best predictor of a building's longevity isn't its construction method, but its continued integration within a community's life. If a building is valued, people in the community will maintain it - and repurpose it again and again as context demands. Conversely if a building isn't valued by the community, it will be lost. No matter how it was built.

[Jack Loudon]

Non-historically significant buildings and other structures usually get demolished because they are no longer suitable for modern life. Bridges are too narrow or otherwise unsafe for our bigger faster vehicles. Old office buildings generally have few of the amenities we now expect, and it's usually not cost-effective to retrofit elevators, HVAC & fire sprinkler systems, seismic upgrades, parking structures, etc.

Same with older houses. My mom's house was built by her dad in 1913, and she was born there 7 years later. It has small bedrooms with no closet space. Single pane windows, no insulation, knob & tube wiring, wood stove & electric wall heaters, old galvanized plumbing, antiquated bathroom, terrible kitchen layout, and on and on. When mom is gone (she still lives there, with our help) my siblings and I will be faced with a dilemma; should we demolish it and build a new house or remodel the existing one? The cost would be similar, but the new house would be more comfortable with a nicer layout. In the past I've been involved in big renovations that made me wonder why I didn't just tear the building down and start from scratch. Sounds a lot like some old wooden boats.

[heimlaga]

I work partly in the building restoration trade.
My oppinion is that a building with a solid and well built framework in reasonable condition on a solid foundation is almost always worth rebuilding. Mainly because modern foundations and modern frames are made for a rather short lifespan so the old building getting a half life upgrade may in fact have more serviceable years ahead of it than a new building has. On the other hand shoddily built or rotted out old buildings are only worth the effort to rebuild if they have some sort of historic value which is enough recognized to make someone willing to pay.

In my oppinion modern house layouts are just as stupid and impractical as the old ones. Only in a different way. When you know both worlds is becomes obvious that humans often disregard practicality for what is perceived as modern. Both then and now. Just look at a modern kitchen sink or at a modern open floor plan or at an old American or English sliding sash window or at an old Swedish kitchen fireplace or an old Finnish entrance door and you will realize that humans are as prone to come up with stupid ideas whatever age or country they live in.

[George Jung]

Interesting, heimlaga; care to expand? Particularly

In my oppinion modern house layouts are just as stupid and impractical as the old ones. Only in a different way. When you know both worlds is becomes obvious that humans often disregard practicality for what is perceived as modern. Both then and now. Just look at a modern kitchen sink or at a modern open floor plan or at an old American or English sliding sash window or at an old Swedish kitchen fireplace or an old Finnish entrance door and you will realize that humans are as prone to come up with stupid ideas whatever age or country they live in.

IYO, what is a practical, smart layout?

[CWSmith]

won't last as long as these:

And we wouldn't want them to.

[Keith Wilson]

Bit of selection bias in the initial posts. The overwhelming majority of Roman buildings are no longer there. Will one in 50,000 of our current buildings be around in a millennium or two?