I apologize for the vagueness in the title, I will explain what I mean in here. In my world, I am thinking that in the future, the path of buildings started to go into building deeper underground, instead of just making taller skyscrapers. Kinda like inverted skyscrapers.

How advantageous would be building into the underground be compared to building into the sky. And how exactly can this be made safe and sustainable, in terms of air, CO2-O2 Levels, and heating? Does this list even make logical or practical sense for a society to do?

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    $\begingroup$ Eventually you hit the local water table, at which point down stops being much of advantage. $\endgroup$
    – John
    Dec 31, 2021 at 3:21
  • $\begingroup$ @Zoey Just as it makes little sense to build a sity of many separate skyscrapers, it makes little sense to build a city of many separate deep underground spaces. Just as it makes sense to build a city with one gigantic city wide skyscraper, it makes more sense to build a city with one gigantic city wide multilevel underground building. $\endgroup$ Dec 31, 2021 at 20:52

3 Answers 3


There are advantages and disadvantages, as in everything. In some cases the same aspect can be a pro and a con.


  • better insulation: the deeper you go, the more stable is the temperature year around. No need to worry about seasonal temperature excursion.
  • better protection: there are way less weathering agents underground. That's why we find fossils and ruins there


  • access to natural light: you can basically forget about it
  • air: getting fresh air becomes tricky, plus you want to avoid exposure to radon for its radioactivity
  • heat management: the better insulation means that, in the event of a fire, cooling the involved volume will take much longer. Also, with a geothermal gradient of 25 C/km, environments get uncomfortably warm pretty soon.
  • radioactivity: depending on the layers you are digging into, you might be surrounded by radioactive products (see radon)
  • waste management: while I can imagine that engineering the management of a toilet flush from the restroom on the top of Burj Khalifa has its head-scratches, underground it becomes more tricky, because you become the lowest point almost naturally.
  • volume management: on the surface if you need more space you have it basically for free, underground you need to dig it.

Summing up, I think the energetic balance is in the negative: what you save in heating is lost in what you need to put in for ventilation, illumination, flow and transport, without accounting for the building itself.

  • $\begingroup$ I see, well as I see it the having to dig becomes less of an issue due to an increase in technology making it easier to mine it away. But yeah, heat was one issue I was worried about, in what ways can you cool it down? $\endgroup$
    – Zoey
    Dec 31, 2021 at 5:03
  • $\begingroup$ @Zoey: The ways to remove heat from underground are: (1) movement of air, for low temperature heat or (2) refrigeration cooling. In both options cool air is sent underground & then returned to the surface but at a location that is distant from the air intakes for the underground infrastructure. $\endgroup$
    – user81881
    Dec 31, 2021 at 12:04
  • $\begingroup$ @L. Dutch 1) Natural light is overrated, at least in the opinion of people who have skin cancer from it. 5) I believe there are toilets designed to vaporize waste water, which could then be expelled to the surface through ventillation shafts. $\endgroup$ Dec 31, 2021 at 20:48
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    $\begingroup$ That is actually a pretty decent idea, vaporizing the waste so that it would be able to be sent up shafts far easier than liquids or solids. But there would then be the issues of high amounts of required energy. $\endgroup$
    – Zoey
    Jan 1, 2022 at 0:59

World specific reasons?

There are circumstances which might exist on your world that are rare on Earth, and which might favor downwards building. Examples:

1: Very high winds on the surface stress the building. Underground there is no wind.

2: Solar radiation is bad on the surface. Underground the substrate shields you.

3: It is very cold on top. Underground the substrate insulates you.

4: There are dangers in space that are looking for you. It is hard to see you underground.

  1. There already exist underground structures on this world that are easy to press into service as dwellings. Animal burrows? Alien ruins? This one is my favorite, because these underground structures have much more space than you need. It is not clear how far down they go.
  • $\begingroup$ Mostly that building taller began to get to the point where going taller started to become very disadvantageous. Moreso they reached the practical limit of building taller. It is also part of a type of zeitgeist or trend. In terms of pollution it isn't as bad as many future works, but isn't really a utopia either, it just had people actually work somewhat to try to find better energy methods, with nuclear power becoming popular. $\endgroup$
    – Zoey
    Dec 31, 2021 at 20:46

One way to handle the problems with building a city deep underground would be to build a city on and above the surface with a really deep city wide basement.

If the air in the vast basement region is always at the same temperature, it can be sucked up and circulated near the ceilings in the summer to cool rooms down, and sucked up and circulted near the floors in the winter to warm rooms up.

Additional heating and cooling of the air from underground would be necessary at times, and would be most efficient if done by neighborhood or city scale heating and cooling units.

Presumably the vast city basement would also contain vast pools or tanks of waters, since water retrains heat, and it would further moderate the air temperatures in the basement.

New air would need to be sucked into the vast underground basement and should be sucked through filters to filter out dust, pollen, spores, and various undesirable gases.

And the streets of the city could be underground, connecting the basements of the various buildings in the top levelof the city wide basement, and there could be storm shelters in the top levels, while most of the basement levels would be vast air spaces.

And such cities might be the first steps to building totally underground cities.


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