[defrost]

The novel, as I recall, didn't start out stratified by wealth etc. It begins with a new arrival to a recently completed high-rise building.

The wikipedia page, for what that's worth, appears to agree:

     Life in the high-rise begins to degenerate quickly, as minor power failures and petty grievances among neighbours and between rival floors escalate into an orgy of violence. Skirmishes become frequent throughout the building as whole floors of tenants try to claim lifts and hold them for their own. Groups gather to defend their rights to the swimming pools, and party-goers attack "enemy floors" to raid and vandalise them.

The outcome is as you recall:

    The lower, middle, and upper floors of the building gradually stratify into distinct groups.

I believe it's a thesis of Ballard's that no matter the initial state social systems evolve (for the worse) into stratified rivalries, I suspect this may have been burnt into his soul by his experieces as a young boy interned during Japanese occupation.

~ https://en.wikipedia.org/wiki/High-Rise_(novel)

[radarsat1]

Nice thanks for that, it's been a while since both I read the novel and saw the film. That's actually a much more nuanced and intriguing take. I might have to reread it now! This article makes me want to read the rest of his works, too.