Why you should never put a pool on your terrace, explained with structural calculations by an architect

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With the arrival of heat and summer, it is possible that many people wonder: Can I put a pool on my terrace or balcony?

The short answer: NO.

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The long answer: join me on this exciting journey of loads and structural calculations

Dubai takes the record for the deepest pool in the world with a dizzying depth of 60 meters

Why can’t I put a pool on my terrace?

The fundamental reason why a pool should not be placed on a terrace is because it was not designed to hold your weight. What happens is that with that answer we don’t get an idea with how much more weight we are overloading the structure.

Let’s do some quick numbers. A circular inflatable pool with a diameter of 3 meters and a height of 76 centimeters like this one from Amazon has an advertised capacity of 3,600 liters if it is filled to 90% (it is not completely cylindrical, otherwise it would be 4,836 liters).

Inflatable Pool Terrace

An inflatable pool has a mass of 500 kg/m2; the floor of the terrace is designed to withstand 200 kg/m2.

Knowing that the density of water is approximately one kilogram per liter, that is 3,600 kg of mass (3.5 tonswhich is more impressive) spread over an area of ​​7.07 m2, which comes out 509kg/m2.

Do you know what calculation overload is? Technical Building Code (page 9.) for a terrace in a residential building? 200kg/m2. (Actually 2 kN/m2 because they are loads, not masses, but I have changed the units -and rounded- so that it is understood).

That is, with a pool of that size we are making the structure withstand more than twice the load for which it was designed.

This tweet sums it up nicely using more visual units of measure.

This also applies to smaller pools, because it is a matter of weight per surface area. Any pool that is filled 50 centimeters will have a mass of 500 kg/m2 and, therefore, it will suppose an overload of two and a half times that foreseen.

A pool with 50 cm of water weighs 2.5 times what the structure is capable of supporting.

For the calculation we have ignored the weight of the people who would enter the pool, but let’s assume that we fill it to 90% with them inside and that the density of the human body is not very different from that of water.

But what about the safety factors or the redistribution of loads?

It is true that in the calculations are introduced safety coefficients, but those are there for, well, security. In case the materials do not behave as expected, to assume imperfections or construction defects, irregular distribution of loads, loss of bearing capacity due to exhaustion… In addition, they are never greater than two. Even counting on this coefficient, we are taking the floor to the limit (what is under the floor of the terrace) and even the beams and pillars.

When it comes to inflatable pools, not even safety factors or load distribution are enough.

On the other hand, we must also consider that the forged have a compression layer that redistributes the load so that it is assumed by a greater part of the structure, but this layer is more designed to distribute specific loads, such as a shelf or a bathtub. In fact, speaking of bathtubs, which are mentioned a lot in these cases: filling the bathtub is usually about 200 liters of water (aka, 200 kg), a much smaller mass that can also be easily distributed, nothing comparable to 3.5 tons of water.

So, what inflatable pool can I put on my terrace?

Baby Pool

Continuing with the numbers that we have done before, theoretically we could put any pool on the terrace as long as we did not fill it with more than 20 cm (that gives the 2 kN/m2 maximum load). But of course, that’s literally a foot of water. And there, in addition, the occupants of the pool (75 kg per adult) should be added to the calculation, because we cannot consider them submerged in an inch of water.

So keeping that in mind, the biggest pool we should put on the terrace is a small one for babies and fill it at most up to 20 centimeters high.

Even with a baby pool the loads can exceed those anticipated in the structure

For example, in a pool like this one with a diameter of 120 cm and a height of 30 cm, up to 340 liters can fit if we fill it to the top.

An abyss of 50 meters and 43,000 cubic meters of water: the deepest pool in the world will be for extreme diving and space flight simulation

That is already 3 kN/m2 (300 kg/m2 to understand us), 50% more calculation overhead. What happens is that, in this case, the compression layer is more effective in redistributing the load, so for calculation purposes we can consider that it is distributed over a larger surface than that occupied by the pool. Even so, it is appropriate not to fill them beyond 20 centimetersbecause the pool is not the only thing on a terrace.

In the case of balconies, a linear overload of 2 kN/m at the edge of the floor is added to the calculation, that is, they are calculated to support a little more weight. However, we have preferred not to consider it for different reasons: on the balconies we crowd more, so there are more loads apart from the pool, and this linear load usually has more effect on the calculation of the beams and columns than on the floor. , which is what usually yields when it comes to pools in places where it does not touch.

Well, my brother-in-law has one on his terrace and it hasn’t fallen.

And a man who smoked like a carter lived to be 105 years old.

The terraces with swimming pools fall. Happens.

So no swimming pools on terraces and balconies. Please. If you want to cool off, a hose or, at most, a “bathtub” or its equivalent volume on the terrace.

With the arrival of heat and summer, it is possible that many people wonder: Can I put a pool on…

With the arrival of heat and summer, it is possible that many people wonder: Can I put a pool on…

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