Probably the roofs aren’t built to withstand all of the added weight.
Who wants to climb all those stairs if elevators are not to be had?
Prime real estate for such ventures is ground level where people can drop in, drop out and see whatever and whoever is on the street.

I’m also thinking it’s a liability if you have hyper kids running around. Maybe insurance is extra expensive for a space on a rooftop for that reason.

Thanks for the great answers so far.

@kritiper “Probably the roofs aren’t built to withstand all of the added weight.”

I should have been more clear. I’m not asking why they aren’t retrofitted onto existing buildings (because you’re correct, it would be a bad idea to throw something like that up on a building not designed to handle the load), but rather why they’re not a typical feature just like a garage might be on most homes and designed from the beginning to have proper support.

Many office and residential; buildings house air conditioner, heat exchanger, and exhaust fan outlets on the roof. Sometimes water tanks for gravity feed systems. All of which can be noisy, and not amenable to calmness and sport.

Some states like Hawaii; the rooftops are for solar panels, someplaces every square foot they fit them

@gorillapaws, in snow country, at least, you want a sloping roof so snow doesn’t accumulate. It’s pretty heavy stuff. You also want rain to run off. Where it stays warm all the time, and especially warm and dry, we do see a lot of flat roofs, right?

there is also the point that people may not feel safe being on a roof or that it may be used for people to meet and do illegal stuff, so you would have to pay to have cameras on the roof and pay someone to monitor those cameras.

In certain places buildings were designed for rooftop use, especially in preindustrial societies, where rooftops would be cooler and/or breezier at night for sleeping.

Flat roofs tend to be expensive and have more problems. It probably varies by state somewhat.

Many building do take advantage of roof tops:

In NYC there are lots of buildings with rooftop areas for people to socialize. I have an old photo of my mom and grandmother on the rooftop laying in the sun getting a tan.

Memphis has plenty of hotels with rooftop bars.

In Florida there are quite a lot of rooftop pools

Also, Nashville has modern homes that are two and three story with rooftop terraces all over the city.

I have heard of rooftop gardens to lower fuel costs to keep the building cooler. I don’t know how prevalent it is.

In northern cities an angled roof makes more sense on a house so the snow falls off as others have mentioned. Snow is very heavy and roofs collapse more than you might think.

I think a big factor is they are used in dense, urban, cities where land is extremely expensive. If land isn’t very expensive it’s much cheaper to just use the land rather than the roof for entertainment space.

Lots of great points here.

@elbanditoroso “Many office and residential; buildings house air conditioner, heat exchanger, and exhaust fan outlets on the roof. Sometimes water tanks for gravity feed systems. All of which can be noisy, and not amenable to calmness and sport.”

This is a really good point. Where do hotels and other buildings with rooftop restaurants/pools/bars/etc. put all of this stuff? Is it in a walled-off section on the roof? The basement? Somewhere else?

@Jeruba “in snow country, at least, you want a sloping roof so snow doesn’t accumulate. It’s pretty heavy stuff. You also want rain to run off. Where it stays warm all the time, and especially warm and dry, we do see a lot of flat roofs, right?”

Couldn’t this be addressed with some kind of seasonal canopy?

@gorillapaws: From what I can see, when a building has a rooftop recreation area, they still have the air conditioning unit on the roof, along with the top of the elevator, etc. The recreation area is not the entire rooftop.

There’s a building in the Bronx that has a rooftop rec area with a canopy. I’ll see if I can find it and link it.

I’m just remembering so many rooftops now. The Thayer Hotel on post at West Point has a bar, the Zulu Time Roof Top Bar.

Metropolitan Museum of Art roof top cafe and garden over looking Central Park. I actually started to search the link for this for you and came across a whole website of rooftops around the world. Here it is: https://www.therooftopguide.com/rooftop-bars-in-new-york/the-cantor-roof-garden-bar.html

There are tons of examples.

If there is an air conditioning unit that only takes up part of the room.

In trying to find the Bronx building that I can see when I drive down to NYC, here’s a link of new buildings with rooftop pools. It will give you an idea of the insane NYC rents, too.

https://www.cityrealty.com/nyc/market-insight/rental-building-offers/gowanus/top-10-coolest-rental-rooftop-pools-nyc/20282

In my neighborhood where 3— or 4-flat apartments were being replaced with single-family homes or new 3-condo buildings, they usually put a patio on top of the garage (a separate structure) in back.

In a denser neighborhood where I knew people building 3— or 4-flat condos, they usually did included a roof-top deck. Either was sold as a communal amenity for all the units, or it was part of the much more expensive top-floor “penthouse”.

@Call_Me_Jay That’s pretty awesome. What state are you in?

@gorillapaws Those are Chicago buildings.

@gorillapaws, look here, and note item 7 in particular.

Water is very heavy stuff, and snow is water, but in a form that allows it to pile up in places where running water could not.

After you’ve shoveled a few front sidewalks in snow up to your waist, you acquire some respect for how dense it can be, the wet, sticky stuff and not the pretty powder, and how much muscle it takes to move it around. I can’t imagine a canopy that would stand up to it.

As a kid you’re taught not to walk close to buildings or stand beneath the eaves when there’s snow on the roof because there could be an avalanche at any time that could injure or bury you. Have you ever been inside a house when a great slide of snow suddenly detached from the roof and thundered down outside the window? It’s not trivial.

When you look at all the millions of structures arrayed across snow county in thousands of cities and towns across six or maybe seven continents, the consistency of sloping roof design suggests that there’s some accumulated wisdom behind it.

It was tried & didn’t go over very well, but I don’t remember WHY they stopped doing it. I think they stopped after the penthouses became popular & anyone who owned a penthouse didn’t want to maintain a garden nor sit out in the sweltering heat. Go back to movies between the late 60’s to mid 80’s, a lot of NYC apartment buildings had rooftops rented out to certain tenants to use for partying & whatever else suited them. I do remember rooftop gardens being popular…I just don’t remember exactly when they stopped being popular. My guess it was when air conditioning became all the rage. Nobody wants to sit outside when it’s 98 degrees outside with 98% humidity.