Swimming pools and coronavirus confinement

Today more than ever Socrates' famous phrase "I only know that I know nothing" is rather relevant. The coronavirus crisis in Spain has left us all on standby and even though the recovery has begun, the situation remains without much certainty, not knowing if we will have guaranteed health around the corner, if we will keep our jobs or, on a more trivvial note, if we will be able to go on holiday this summer.

The most prudent amongst us are already seeing the reality that no, this year there will be no holidays to the Caribbean and perhaps not even to your favourite beach in Almería. However, for this precise reason, enquiries about houses with swimming pools are soaring. According to idealista data, visits to real estate listings of houses for sale with swimming pools reached 29% of the total visits to houses for sale in the month of April, which gives a year-on-year increase of nearly four percentage points. 

In normal circumstances, if in the big cities you're lucky enough to have a pool in summer, (and you suddenly become popular amongst your friends), what can we say about those who have a pool this summer of 2020 in which movements will be limited by the coronavirus.

If the purchase of a property with a pool is not feasible and is simply just a dream for now, or if you don't have a holiday home, perhaps many are considering placing or installing a pool in their garden. Sounds perfect. But beware of placing it on a terrace or balcony because you may run into problems. With the help of architect José Ramón Hernández, let's have a look at how to safely have a swimming pool at home.

Let's talk about the technical details of structures and loads first: "When calculating the structure of a building, all the loads it will have to bear are taken into account. On the one hand, those that are fixed, certain and constant are considered: the weight of the structure itself, that of the flooring and that of all the construction materials. On the other hand, those that may or may not be present are evaluated, those that are variable and inconstant: these are called overloads (wind, snow, use etc...). In a conventional residential building, the overloads of use that are estimated are 2 kN/m2 (kilonewtons per m2), which are approximately about 200 kilograms-force per m2 (203.9 kg/m2). Not to be confused: a house is designed to withstand, in addition to what it already weighs with all its materials, 200 kg/m2", he explains.

"A swimming pool, just like a piece of furniture, a group of people, etc., is considered to be overloaded with use, and has to carry a maximum of those 200 kg/m2 that have been considered for the calculation. This, in a swimming pool, is equivalent to a layer of water 20cm high. If we think about a 50cm pool we have to know that it will load about 500kg/m2. One of 70cm, 700 kg/m2, and one of 1 metre in height will load 1000kg/m2. This is much more than what was taken into account when calculating the structure of the building," he warns.

At this point it should be clarified that to the load calculation estimates, that is, those we have seen before, a safety coefficient is applied that increases them. And to the resistance of the materials (steel and concrete) another coefficient is applied that reduces their true resistance. Therefore, we are in an area that plays with a good safety margin. "But these safety margins are there to be maintained, not to be rushed," he says.

At this point some may be thinking that the pool will not occupy the entire terrace, and that is correct. "The estimated overload of 200 kg/m2 is over the entire surface of the floor. For example, it is not that someone weighing more than 100kg, hugs another person of a similar weight and in the living room, and they already respresent 200kg in one m2, but consider that in every square metre of the living room, the house and the whole building there are two 100kg individuals embracing each other. In that sense, you have to think that the pool does not occupy the whole terrace, nor the whole floor of the building, it is true, and that is why it does not behave as a uniform surface load, but as a punctual load".

"It's as if we put a huge pot with a tree, or a statue, on the terrace. We have to see how many kilos (often more than a ton) we are putting on the terrace without being aware of it. This will cause the structure to behave in an unexpected way," the architect explains.

What dangers can a punctual load pose?

"In general, we are not talking about the terrace sinking or collapsing (although there have been cases), but about the deformation of the floor, and therefore of the ceiling on the lower floor, as well as the cracking of partitions, the detachment of suspended ceilings, the breaking of tiles on the terrace, etc. The state of conservation of the building, its previous defects, etc. must also be taken into account".

In short, the architect explains, "putting a swimming pool on a terrace or rooftop is a risky thing to do. A technician should be consulted first. I wouldn't put it in my house, and I certainly wouldn't be at ease if my upstairs neighbour put it there. The most I would dare to do would be to put one for small children, pools that are more like a big bowl", concludes the architect, who is sure that the pools themselves have manuals with warnings advising them to be installed on firm ground and not on the structure of any building.