ᐅ Load-bearing capacity of terraces for hot tubs – any experiences?

Dear all,

I live in a top-floor apartment and have a terrace at the same level as my living area. I would like to install a hot tub on the terrace.

Information from the structural engineer:
The design loads for the terraces on the top floor were specified as a dead load of g2 = 1.9 kN/m² and a live load of q = 3.2 kN/m².

I looked it up and understand that this corresponds to 320 kg per square meter (sq m).

I have three questions:

1) It seems that the dead load is not relevant for me—am I correct?

2) The 320 kg per sq m represents the minimum load the terrace must safely support. Typically, how much over this value is generally acceptable without issues?

3) The terrace area is 20 sq m, and the hot tub covers 5.3 sq m. Since roughly 15 sq m will have no load, am I right to assume that the 5 sq m area with the hot tub can bear significantly more load than if the entire 20 sq m were loaded?

Thank you very much in advance for any answers! I welcome multiple or differing opinions.

Best regards,
Thomas

Thomasberger schrieb:

The terrace is 20 sqm (215 sq ft). The hot tub is 5.3 sqm (57 sq ft). Since about 15 sqm (161 sq ft) remain unloaded, am I correct in assuming that the 5 sqm (54 sq ft) area can bear a much higher load than if the entire 20 sqm (215 sq ft) were loaded?

This is an area load that does not increase because of free-standing parts.
Your weight, the empty weight of the pool, and the water all add up.
It may be that you can only fill it with 20 cm (8 inches) of water, and then important parts of you are no longer submerged.
In short, forget it.

You are mistaken; it is the specification in kilograms per square meter that is the limiting factor.

Simply put, the smallest step your wife takes hurts more than an elephant stepping on you.

For reference, 1 by 1 meter and 10 cm (4 inches) already equals 100 kg (220 lbs). Now add yourself and your wife/girlfriend sitting there. At this point, the load of 320 kg per square meter is nearly reached, and you are only just wet.

Unfortunately, this kind of collapse happens quite often.

Um, when a person is in the pool, they displace the water. Water weighs roughly the same as the mass of the person being displaced.

Could someone who is a structural engineer, knows one, or has discussed this topic please answer only this?

2) The 320 kg per square meter is the minimum load that the terrace must support. How much above the value given by the structural engineer is typically acceptable without problems?

THANK YOU,
Thomas

Thomasberger schrieb:

Can someone who is a structural engineer, knows one, or has spoken with one please just answer this?

What do you expect? That this structural engineer then says his colleague was just talking nonsense before?

Thomasberger schrieb:

2) The 320 kg per sqm (about 314 kg actually) is the minimum load the terrace must withstand. How much more than the value given by the structural engineer is usually not a problem?

Let me explain slowly:

If 320 kg per m² (about 314 kg actually, but I don’t want to be holier than the pope) is specified, then that is the decisive value — and that corresponds roughly to about 30 cm (12 inches) of water on the terrace WITHOUT a person sitting in it (the pool itself also has some weight).

The advantage of physics is that it doesn’t argue — as an engineer and a good friend of a structural engineer, I’ve never encountered alternative mechanics or traditional Chinese thermodynamics. She still laughs about it.

On such surfaces, often even children’s paddling pools are not allowed (today’s standards often require about 400 kg per m² (about 390 lbs per sq ft)).

Summary: avoid it — just don’t do it. Because if it collapses, no insurance will cover the damages, since you knowingly built something unsafe.

Thomasberger schrieb:

Um, when a person is in the pool, they displace the water. Water weighs about the same as the mass of the person they displace.

That means if the water level reaches 30cm (12 inches), you are definitely at the load limit, regardless of whether a person is inside.

Thomasberger schrieb:

The 320 kg per m² (66.0 lbs per ft²) is the minimum load capacity the terrace must withstand. How much more than the value specified by the structural engineer is usually not a problem?

For insurance, 0%,
up to 500-1000% before collapse in a new building,
but then you would have to pay for all the damages yourself.