Rooftop pools: what do they weigh? What kind of reinforcemnet?

Factual Questions
1

I love swimming and pretty much the only thing I care about when I do my real estate porn is the pools. (Favorite house on the front page. Except it has no pool!)

Today’s pools in Huffpo LA are hotels, and a couple of them are rooftop. Rooftop pools amaze and scare me. Water is heavy. A pool of water is very heavy. How are these things built? What kind of reinforcement is needed? Obviously the actual pool itself must be pre-molded fiberglass or something similar, and how well does that hold up to earthquakes?

And how much does an average-sized fiberglass pool filled with water weigh?

2

Water weighs around 8 lbs/gallon. A decent sized residential pool might be 20,000 gallons, so the water would weigh 160,000 lbs or 80 tons.

3

Yikes! 80 tons at the top of a building???

4

I think 20,000 gallons would be a lot for a rooftop pool. Looking at those pictures, most are pretty small and not very deep. Unfortunately, it’s hard to get real facts on how big they are.

5

Well, buildings are strong - just think about a parking garage…

Even a residential building is designed for a floor load of 40 lbs / square foot, so a 2,000 square foot apartment would be designed to support 40 tons.

6

Naaaaw. Rooftop pools are so 90s.

Think rooftop cantilevered pools!

7

Seemingly every building in New York City has a water tank on its roof, and these things usually hold 5,000-10,000 gallons. They’ve been part of the skyline for the past 100+ years, so it’s no major engineering accomplishment to have that much weight on a rooftop.

8

Cool! Where is that?

9

I always wonder, if I weigh 200 lbs, and stand on the ball of one foot, I’m exerting, say, 1600 pounds per square foot on the floor, and yet don’t fall through it. :stuck_out_tongue:

10

Madrid
http://www.treehugger.com/files/2009/03/hemeroscopium-house.php

11

not a structural engineer but i worked with design and feasibility. a building can stand the weight of a swimming pool (compressive force) but the question is what happens during an earthquake. the building will sway excessively with all that weight at the top and concrete is weak when it comes to tension/shearing forces. so they put a seismic line on both lateral axes of the pool to allow for some movement. a 2-inch gap or something like that.

12

If the ball of your foot measures 2" x 3", you’re exerting 33.333 pounds per square inch, which equals 4800 lbs. per square foot.

13

If you think that’s cool, check out thisone!

14

Those pools double as water storage for fire suppression, don’t they?

15

A few hotels I’ve stayed at had concrete rooftop pools. They were built over the parking decks.

16

Pool volume calculator here. I tried the “inground rectangle” form, with A=20’, B=40’, shallow-depth = 4’, and deep-depth = 12’. Came up with 48,000 galons; at 8.3 pounds per gallon, that’s 499,758 pounds of water.

For some realistic numbers, These guys build prefab lofted pools. Their dimensions are as big as 14x40 feet. This one is 14’x40’, average depth 45 inches (3.75’). That’s 15,760 gallons, 131,000 pounds of water.