The local fire laws state there has to be easy egress from all levels. I can just image being on the 30th underground level and having a fire break out.
And no basement room can be counted as a bedroom.
Well, yes you can. In fact, this site has a whole lot of them listed. Although they seem to be going fast.
As for a private island, just go and take a look and pick one you like. That site has them listed all over the world.
What, they don’t have anything in the Canary Islands? Damn, I thought I have finally located somebody who has one for sale.
Yes, you’d be more likely to hit grounwater on an island, as long as you are close to sea level.
Water tables can sit above or below sea level depending on the soil makeup and other local features, like a large bed of underground clay could hold groundwater water above sea level.
I know you aren’t actually going to doing this, but if your mind is on this kind of stuff consider learning about the water table and how water moves through the soil, the study of this is called hydrology. Water seeks the lowest level, so if you dig below sea level, you must keep an endless onslaught of H2O at bay. If you want your lair on an island, the most structurally sound and environmentally secure option would probably be to find an island with above-ground bedrock, like a mountain, and carve out this lair there to avoid water issues. It depends if you want “underground” to mean below sea level, or just under a geologic surface.
If you want to dig below sea level, you are going to have challenges with water (as well as permits) pretty much anywhere there is rain or snow-melt to fill the pore space of the soil. Bedrock has virtually no pore space because it is solid rock instead of particles of sand or clay etc. so you can carve out a water-tight enclosure. Although the earth is constantly changing, so even solid rock will crack and have water flowing through the cracks at some point, it’s just an issue of when; will it be in 100,000 years when you’re underground anyway, or in 5 years during your Secret Underground Lair Annual Christmas Party?
I wonder how deep he’s dug in twelve years.
Regards,
Shodan
Not quite 30 levels, but “building down” is definitely a thing.
I’ve thought about this a lot and would like to dig a basement hideout. Would be a cool ongoing hobby! 
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How does Mr Armstrong come to find a 12 year old thread which spurs his registration and makes this his initial post?? What is the motivation for ressurected zombie threads by brand new members? Would honestly like to know… :dubious:
Google indexes SDMB quite thoroughly (it’s a complement really – Google has identified SDMB as a good source of information) and we often get new people finding a thread they are looking for directly from a Google search and not noticing the date.
You don’t dig a hole where there isn’t one, you build your structure where there’s already a hole, like an old quarry, and then you fill in around it.
With lava!
You know, if I go to the building permit people and say, “I’d like to build a building a third of a mile long and every exit is going to be at one end of it.” they’d laugh me out of the office, yet if I say I’m going to stand it up on end with all the exits at the bottom all of a sudden there’s no problem. It’s the same issue with your 30 story underground building. Those bottom floors get pretty far from the exits.
Sort of off topic, but I’ve always wanted a giant underground mansion you could only get to through a dilapidated trailer on the surface. So everyone would think you’re poor and have nothing to steal, but when you take the stairs (or elevator) in the bedroom closet, you enter this amazing underground complex. Like the Bat Cave but without the Wayne mansion on top, just a crappy trailer. Or maybe an entire squalid trailer park, for maximum believability. Or an outhouse, or a TARDIS in the woods!
So, for all you asking about the motivation behind this sort of request, besides safety from missiles for third world dictators, there’s also this reason, to cleverly disguise rich people. All I have to do now is get rich…
And yes, I believe old government missile silos out west would be the best choice. You can get them for cheap. Like 10 stories underground for $100k. Of course, you have to build all the floors yourself, increasing the cost quite a bit.
You’ll need to get a couple of chums and a chauffeur so you can form a detective agency as well.
I’ve heard there are buildings 10, 20, even 30 stories above the ground (those top floors get just as far from the exits). I think some of those buildings even have building permits.
To be fair, those buildings usually are regulated to require different features than buildings with only one or two floors.
And furthermore, how long in general does it take for google to discover some new page that appears anywhere on the web? I’ve noticed that new SDMB posts appear in google searches within just a few minutes of being posted! I looks like Google pays special attention to this board. I can’t imagine keeping up with the entire Web that fast!
Ever heard of Forestiere Underground Gardens?
Entire underground mansion (well, not 30 stories I don’t think), hand-built by Italian immigrant Baldasare Forestiere in Fresno, Ca. Okay, this site mentions it’s three levels. I imagine it was a ways out in the country when it was built but is definitely in a fairly built-up area of Fresno now, with a major thoroughfare passing right by it. (I imagine the same about the Winchester Mystery House too.)
From this major thoroughfare, the place looks like a nearly vacant lot, with some scattered scruffy trees and shrubbery. I’ve been told those are actually the tops of underground trees and shrubs sticking up through open skylights. There’s a large sign at one corner saying “Forestiere Underground Gardens” but it looks very old and weathered and faded – like some ancient long-abandoned business or something. Not at all inviting looking.
I like your style.
If I had obscene amounts of money I’d buy a mountain and hollow it out. My home would be accessible from a tunnel at the base and would extend upward to an observation deck poking out of the summit.
Building a hobbit-hole in a hillside with the entrance at the bottom and the inside floors higher than that is also a good design, as it keeps the rain from running in.
After thinking about it for twelve years, I suggest that you don’t try this in a suburb. The building department/permit center/whatever will not want you doing anything that could affect your neighbors, and if you hit, say, a sand pocket a hundred feet down, it will affect them in a big way; also they’ll mostly be checking your plans to see that they meet standard regs. There are no standard regulations for digging down that far.
Try someplace out away from other houses. And outside city limits. Prepare to have to pay big bucks for geotechnical reports and structural engineering reports. If you’re in a hurry, start the geotechnical testing at multiple locations, in case some of them turn out to be infeasible.
If you start to feel lonely, you can build a suburb around your house later, after it’s proved to be stable.