Then later on in the film Victoria goes skinny dipping in the pool. This turns out to be a dream but it still raises the question that with no equipment would they really be able to live that high in the atmosphere? and use the pool without getting hypothermia?
Like the Jetsons, their homes were still attached to earth, it shows this at one point when one of the "Aliens", of the movie is looking at it from the ground, you see a giant tripod or stand at the base, that has a pole extending into the sky. The loss of the moon particularly creates properties on earth that we're not aware of such as cloud layer level changes, new gravitational properties, etc.
After Julia is rescued and taken to the Sky Tower, we see a panning shot of one of the Scavs peering through a pair of binoculars up at the house from ground level. It doesn't really appear to be all that high and was perhaps on par with a medium-sized skyscraper. It could be that the tower itself is constructed on elevated ground. We later see Tech 52's house which is on a mountain top but does not rest on top of a huge tower.
I expect that the altitude ensures that the tech can always be in contact with his communications officer and the house is better placed to contact the Tet.
The house itself is sealed and considering their clothes and the pool, it's also heated. The pool scene is not a dream.
The key things to remember here are:
The house is attached to the ground (via a big pole). Yes, this is entirely unrealistic.
I don't think the pool sequence was a dream.
The house is above the clouds because it looks cool. This is a film, and looking cool trumps being accurate and realistic (like, hey, what happens when they flush their toilet!?!)
They're in the year 2077 -
Look at the little fuel cells they have. One alone could heat the house and pool.
Have you gone outside and seen fog? What is that? It's a cloud; clouds form at all different heights. I lived in Flagstaff, AZ and we would always be above the clouds. And sometimes the clouds would be above us.
Look at the top of the Empire State Building. The top deck is at ground level in the movie.
Someone mentioned the moon changing the atmosphere. Now that I think about it, I've been on top of the stratosphere in Las Vegas and been above clouds.
That said, come on - it's a movie based in 2077 so who knows what tech they have? Look at the hydro rigs and tell me how they send power off planet without cables?