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A common question seems to be how to survive tsunamis / floodings and the like.
However I'm interested in what a building would look like after a year under the water.

Depending on the depth and the increasing pressure, as each part of the building is able to withstand differing amounts of pressure / erosion / animal life encroachment...

Do windows survive for long?
Will wood warp and crack, will doors be able to stay adhered to their frames or would they inevitably float to the surface?

A direct analogy I can draw is with sunk boats, but they're usually designed for more aquatic purposes than buildings, so perhaps not a wholly usable comparison.

What would a building under water truly be like after a year?

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    $\begingroup$ How does the water appear? Is it a slow trickle, or a literal flash flood? Most buildings have openings everywhere that would allow water to get in, which would expose surfaces to water that definitely aren't meant for that but would also even out the pressure quite quickly. $\endgroup$ – a CVn Sep 10 '15 at 8:58
  • $\begingroup$ Would the results be vastly different given the one year submerged? Other than perhaps flash floods shattering windows and causing damage by objects dragged in its wake, I'm mostly wondering what the effect of time on a submerged building would yield. $\endgroup$ – Reaces Sep 10 '15 at 9:00
  • $\begingroup$ Pushing and pulling of wave(harmonic oscillation) is akin to vibration(mechanical resonance) is bad for most surface concrete structures. $\endgroup$ – user6760 Sep 10 '15 at 10:17
  • $\begingroup$ Sea water is more corrosive, that is bad for the metallic structures. $\endgroup$ – Vincent Sep 10 '15 at 14:37
  • $\begingroup$ I think nearly all buildings would faire very badly, even if it's all done gently and carefully. $\endgroup$ – alan2here Sep 10 '15 at 14:59
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It all depends, mostly on the materials used, salinity, pH levels, oxygen concentration, temperature, availability of calcium carbonate and water currents/waves.

These effects are non-linear, for example, corrosion rates generally increase with temperature, but if you raise the temperature further in can slow corrosion by removing oxygen (among other things).

Calcium carbonates (e.g. limestone) in the water can deposit scale that protects the underlying materials. You often see these scales on water pipes. These scales can protect the materials for a long time.

There are many examples of buildings and towns that have been submerged for long periods of time. Many are intentional and result from building reservoirs, but almost all of these are fresh water.

Since we build ships, we have also studied the issues associated with submerged materials used in ships.

Building materials. Sheetrock is rapidly ruined. Wood treated with creosote survives for a long time, 50 or 100 years is usually not ruined. Creosote is not much used anymore for marine applications due to environmental concerns. The other treatments are not as effective, but I don't have actual survival times. Plywood may delaminate within a few years depending upon the glue.

Steel -- Steel used in construction is rarely stainless, so corrosion begins immediately as even fresh water always conducts current. Depending upon the other materials this may be accelerated greatly because of galvanic effects. In fresh water, the rate of corrosion depends upon very minor environmental differences, including the consistency of the steel the result is often pitting where the slightly more corrosive gets used up in preference to the other areas. Experimental data is not even particularly accurate because the results are so variable. Salt water is just a worse problem as electrical conductivity is high.

Some coatings will protect steel for quite a while (even decades), but they all eventually fail due to imperfect coating and leaching of the material. Zinc-dipped steel is best known and for good reason. It is very effective as coverage is nearly perfect and the Zinc will be sacrificed first during corrosion. It will still fail eventually (cracks in the coating, etc.) but I don't expect this to be common in construction. It certainly is not used for the steel fasteners that many constructions depend upon. I.e., once the nails go, the building collapses.

For a nice online guide that gives a hint of the difficulty see Fundamentals of Metallic Corrosion in Fresh Water

Windows may tend to survive better than you might expect because they are frequently designed to resist moisture problems, so the wood is treated and the glues are moisture resistant. Still, just observe the deterioration of a leaky window and you will know that they really don't survive that well.

So what does last? Stone and kiln dried ceramics. You might get thousands of years from some of these. However, the mortar is first common point of failure. Some mortars can fail within a decade, others might last for a hundred years or even somewhat longer. If you have mortarless stone construction and you don't have problems due to earthquakes or excessive currents or wave you could live there when the waters recede a few centuries later.

The end result of all this variability is that we don't simply design construction to last for 50 years in underwater environments. We design the best we can and begin a program of inspection and maintenance. We have to inspect because we don't know when failure will occur and the maintenance is needed because failure will occur if we don't prevent it.


So what about 1 year of submersion. Any structure would require cleaning, refinishing, etc. before it would be usable. Note that most flooding also means sewer overflows are included in the floodwaters. Definite intensive cleanup is required and well as repainting, etc.

In general terms.

Wood -- unless specially treated for water, the wood will be damaged beyond what you would wish to use. This includes most windows as construction materials are often selected based on price rather than quality in residential usage. Plywood is even less likely to be usable as water can interpenetrate common plywood more easily than bulk wood.

Steel -- unless specially treated for water, significant corrosion will be present making the cost of cleanup very high. If steel fasteners are used in construction, it will be unsound (or at least not provably sound)

Brick, concrete, stone -- Most mortars should survive and be safe to use after a year underwater provided they have had sufficient time to cure completely prior to flooding -- still a nasty cleanup job will be needed and the organic materials, etc. will get into every nook and cranny.

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  • $\begingroup$ What about water current? Is this all mostly based on still water? $\endgroup$ – Reaces Sep 10 '15 at 21:15
  • $\begingroup$ Yes, I am pretty much using assuming limited water motion. Currents just accelerate materials breakdown. How much acceleration is once again specific to the remaining circumstances. $\endgroup$ – Gary Walker Sep 11 '15 at 0:06
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The building structure may do OK, but the devil is in the details

Gary Walker gave a good comprehensive description of what will happen to the structural materials - wood, brick, steel, etc. But there is a lot more to a modern building:

  • Electrical

Everything electrical - wiring, HVAC equipment, thermostats, lighting - will fall apart pretty quickly. Circuit breakers (which are much more complex than the fuses of yesteryear), light bulbs (incandescent will (literally) crack under the pressure; CFLs and LEDs will die a quick death as the electronics rot), telephone equipment, alarm systems - even an ordinary "in & out" flood will ruin much of that and extended submersion will ruin it all.

  • Plumbing

Even though plumbing is designed to transport water, many of the parts are not designed to have water on the outside and will corrode.

  • HVAC

In addition to the electrical components (compressors, air handlers, thermostats, control circuits) all becoming junk very quickly, the duct work will rust and/or be covered with mold, algae and other wonderful stuff.

  • Floor Coverings

Carpeting won't last more than a few days. Wood won't last much longer as it starts to warp. Ceramic tile may be the only flooring that lasts the year.

  • Walls

While walls themselves may do OK - particularly brick and stone - paint, wallpaper and other wall treatments would be ruined very quickly. Drywall won't fare well - it doesn't last if it isn't "dry".

  • Miscellaneous

Doors will likely be ruined - steel will rust, wood will warp. Railings, hinges, poles and other hardware will rust or rot. Insulation (fiberglass, foam, etc.) will get really nasty. Plus plenty of other things I haven't thought of yet.

In short, even if a building is structurally sound (doubtful), if you were to somehow get it out of the water after a year it would likely be cheaper to tear it down and start from scratch than to replace every bit of electrical wiring & equipment, HVAC systems and floor covering; clean/dry & repaint all walls; replace doors & windows, plumbing fixtures, etc.

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    $\begingroup$ From personal experience with home flooding, carpet and flooring materials are ruined in a few (less than 6) hours with clean fresh tap water. Drywall ditto. Fiberglass insulation, ditto. $\endgroup$ – pojo-guy Jul 3 '18 at 2:27
  • $\begingroup$ I've seen carpeting dried out professionally after floods. But after a year (even a week) I don't think it has much chance. I forgot about insulation - I'll add that to the answer. $\endgroup$ – manassehkatz Jul 3 '18 at 2:37

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