Dwarves DO live in mountains

[madd0ct0r]

OK. rules.

Tolkienesque world - so european climate, crops and animals. no purple worms.

Renaissance tech, with justifiable developments.

Construction tech look at cathedrals - we've got stone masons, stone saws and heavy winches and bock lifts

Mining tech - chisels, freeze thaw shattering and wet stake splitting



Build a sustainable Dwarven City, Lonely Mountain style.



I've got my own ideas about how a Dwarven city would be slowly built, but I'll see what others say first.

[Dalton]

Man, why limit it to the Lonely Mountain? Look at Moria.

[Serafina]

Sustainable? No problem, just rely heavily on trade.
In real life, larger cities didn't do their farming themselves, they were sustained by the surrounding farmland. Just trade your superior dwarven tools for food.
Realistically you'll need a bit more than just that for trading, but you get the idea.

Self-sustaining? Now that's more tricky. And not just the food either.
People always wonder about the food when talking about underground cities, but actually you need to worry about much more than just that. Where do you get your leather, your wool (or other textiles), your wood and all your other plant/animal-based materials?

The simplest answer is just having a valley that is accessible solely via your underground city, and thus being well-defended. Or having farmland outside your lonely mountain, with the actual habitation inside the mountain. Set down a good road-network, or even use horse/ox-drawn railway-carts, and you can actually have almost all your population underground while still having farmland. With good nightvision you can actually do your farming at night, if you want to stay nocturnal.

If you want to move your farming underground, it gets tricky.
Fishing can be a potential source for food and possibly bones which you can use for crafting.
You can grow mushrooms, but those only provide nutrition and no straw, which is a loss.
You can potentially keep farm animals underground - the artificial illumination will harm them though. Moving them outside during the warm months will be necessary. Then again, you can keep lifestock on alpine ranges, so that fits dwarfen lifestyle very well.
Wood is a severe problem. You don't necessarily need it for heating if you have coal deposits, that's a plus - but you still need it for construction. The scarcity of wood actually provides a nice explanation for the apparent wealth of such a community - for example you might have metal or porcelain-dishes instead of wooden ones simply because they are cheaper than wood ones when wood is scarce. At either rate, that's something you'd most likely have to import.
Since you have no plant matter, several textiles become unavailable, as well as several dies and such.


You will most likely end with the following:
- Scarcity of nutrition. Basic calorie intake might work out, but you'll most likely end up deficient in vitamins. All types of fruit would be highly desirable trade goods.
- Scarcity of textiles and leather. Your only source will be your small lifestock population which you keep overground during the warmer months, correspondingly small for your population. Thus, clothing will be of premium value.
- Absence of plant matter. That affects your textile situation again.
- Absence of wood. That'll force you to build a lot of stuff out of metal which we'd normally build out of wood, with the corresponding challenges in craftsmanship.
All of this can be solved via trade of course.

[fgalkin]

For an underground city, the biggest obstacle isn't food, it's air and light. I don't think you can properly ventillate a city of several thousand with medieval or Renaissance technology.

Given the difficulty of digging in, I doubt there would be any real incentive for the ancient Dwarves to go live underground, any more than there was for ancient humans. I suppose you can start with a set of mountain valleys with a large network of natural caverns (as I've did for a world I made), but you would need a very good reason to have underground-dwelling Dwarves.

Have a very nice day.
-fgalkin

[Zor]

If you want Dwarvish cities to be self self sufficient. One idea i had was Manasynthetic plants that could use background magic in place of light and as such could survive and grow underground.

That said one thing that you should take into consideration, Waste Heat might be an issue. Huge forges underground in confined tunnels. It could get very hot in their.

Zor

[Skgoa]

Many mountains have forests on them and animals often live even farther up than trees grow. And even if this particular mountain doesn't have those, there is no reasons the dwarfs couldn't dig a tunnel to the base of the mountain. (E.g. in Lord of the Rings.) So while mountain-dwelling dwarfs would have a harder time aquiring wood and animal products, it's not nearly as bad as it would seem at first glance. The scarcity of edible plants could be a problem, though. The soil would be far worse than what humans, elves, etc., can use.

For an underground city, the biggest obstacle isn't food, it's air and light. I don't think you can properly ventillate a city of several thousand with medieval or Renaissance technology.

What about using a chimney-like effect? That would also explain the giant chasms.

Given the difficulty of digging in, I doubt there would be any real incentive for the ancient Dwarves to go live underground, any more than there was for ancient humans. I suppose you can start with a set of mountain valleys with a large network of natural caverns (as I've did for a world I made), but you would need a very good reason to have underground-dwelling Dwarves.

Security? Ressources like rare earths and (precious) metals? They might simply have realized at some point that it makes more sense in the long run to stay underground, where there is everything they need to base their livelihoods on, and just trade for whatever they need.

[Eframepilot]

Security? Ressources like rare earths and (precious) metals? They might simply have realized at some point that it makes more sense in the long run to stay underground, where there is everything they need to base their livelihoods on, and just trade for whatever they need.

The engineering difficulties are far far greater than the advantages. The primary reason that fantasy dwarves live underground is cultural, just as how elves live in forests instead of clear-cutting them and building much more efficient cities.

[madd0ct0r]

Well - regarding the elves, Tolkien was pretty clear that they'd shaped the forests around them, that most of the tree species were created and gave 'crops' of some sort or the other.
There was a section where he showed how they spun the bark of one tree to make the magical rope, although it was cut before publication (the whole mysterious beings thing was better literature).

Humans never built cities because they were more efficient, cities just developed naturally from the way humans live together. And so I belive to be the case with Dwarves.


Step 1 – Small groups of families settle on the slopes of the Crag. Some farm the valley, others start to fell trees for timber and a few start prospecting the mountain above for ores. Classic Homesteading Stuff. Principle crops at this time would oats or barley with sheep/goats on the hillside.
With a small and slow growing population, and limited mobility the crofters are quite defensive in nature, relying mostly on wooden stockades.

Step2 – The farming and timber have limited value. They can sustain the local population but there’s little left over for trade. The few seams of ore detected are proving more useful though, with simple 2 dwarf galleries being hacked into the Crag. Streams coming off the Crag are being slowly harnessed for grinding and making flour, and the village smithy does a good trade with passing caravans.

Step3 – A few hundred years later, we are now looking at a small town. Trade is thriving, with all variety of items, but espcially preserved food being imported. Timber is now almost purely for charcoal production. The smithy bellows and main hammer are both waterwheel powered.
The main construction pattern now is Timber poles with stone infill, with larger houses being entirely stone. When you live 250years, you build to last. The main roads are paved and most tracks are sealed with gravel spoil from the mining in the Crag. Chalk quarries have been set up elsewhere in the valley, and quicklime is an important export. Coal is expected to be the next important mined substance.
As the galleries in the crag get deeper, ventilation is becoming more important. A temporary measure is using children to run up and down the narrow galleries to move the air* but several entrepeneurs are toting their chimney or sail based solutions. An agreement for the design, constrcution and interconnection between shafts is expected at the next clanmoot.
Several underground streams that have interfered with the mining have been diverted along spare or old shafts towards the main town resivoir. Some are sugesting that canals within the main galleries could be effcient for moving goods and tempreture control, others that water from lower in the valley might be pumped to resivoir by use of windmills.


*actually done in real life


Step4 – The town has fortified walls (built as two stone walls sandwiching a dense layer of minespoil), and a keep that backs onto the Crag. Numerous old mineshafts now run directly into the keep, and the growing interconnections between tunnels has led to additonal outposts and covered areas being built up the mountain. The terraces for farming have been gradually upgraded over the years with the available stone and are now used for both wet and dry crop cultivation, water storage and as foundations for wealthy family homes. As with the Keep, most of these homes will use a tunnel connection to the main network for times of seige or dangerous weather.
Deep water canals circulate through the mountain and layers of the keep, providing low but consistent power to numerous waterwheels, sanitation, a fire safety system and a high level of climate stability.
Some of these canals are entire old mineshafts. They were partially flooded, and then sections hewed from the ceiling straight into the boat for transport out. The blocks were mostly intended for building, and spilt out using the blocks own weight and careful crack patterns from chisels. In this way, the tunnel above the ‘canal’ was cut rapidly, forming a larger tunnel with wide pavements either side of the canal.

Step 5 – As hundred and hundreds of years pass, the Crag becomes largely hollowed out, with great arching halls where once there were galleries. It is unclear wether the Keep has receeded into the mountain or the mountain has grown outwards to encompass the keep. Every inch of the Crag’s surface seems to have been built upon or put to use many times over. Even so, the bulk of the population live inside the Crag itself. As each wave of invaders has washed against the walls the people have been safe inside, and after each invasion as many stay to work and live inside as return to the less stable perimeter.

[Zixinus]

Another problem is sewage and trash?

You'll have to pump that shit (and worse) out (and I guess you need water for it?). Where will you pump it and how? Deep underground?

Then there is trash. Some of it probably will be reusable, but how much?

Oh dear, I might be channeling Shroom here but... will dwarves make some of their walls out of trash and their shit? Like, as an extra defense measure against invaders, if they manage to break the wall, they'll have a small avalaunche of centuries of dwarven shit and piss land on them?

[Skgoa]

Throw it in the lava.

[Sea Skimmer]

What about using a chimney-like effect? That would also explain the giant chasms.

Early coal mines were actually ventilated with that effect. You'd have a system of doors and vent ducts to make it such that a nice big fire was constantly pulling fresh air to the working face of the mine. The Dwarven foundries could actually be an integral part of keeping the tunnels habitable by ventilating them. The massive cost of lighting would be a bigger problem, candles would get absurdly expensive and lots of open fires would be a serious problem, as are large numbers of light shafts, which would have limited effectiveness anyway.

Throw it in the lava.

Or just burn it all, once you have serious fires burning trash and waste wouldn't be that big a deal. They might also backfill unwanted tunnels with debris and such, and ash from the fires. Course, one issue also is, what on earth are they doing with all the rock being cut to dig the tunnels in the first place? Complexes like Moria would have completely massive piles of debris outside of them, but this never seems to get much mention. Some good stone might be hauled off to build surface structures, but you'd have lots and lots of gravel thats good for nothing but fill, and very hard to haul any distance.

[madd0ct0r]

ok. in reverse order:

Spoil heaps - i think i touched on that in my post. Gravel goes for roads and concrete. A trading nation will have a vested interest in having good road access and it's an easy way to get rid of huge quantities of gravel. (maybe they used it to fill some of the natural chasms in Moria?)

Lighting - not something I'd really considered. I seem to recall dwarves having good night sight, so the problem is reduced in magnitude compared to humans. At the moment I'm going to go for oil lamps with later progression to gas lamps. I've found some sources claiming some mines used rotting fish for phosphorescent lighting in real life. Perhaps (yet another) use for the canals?
(fireflies are cute, but they don't really produce enough light, seen it myself)

Sewage
- option 1 - dump it in the canal (suitable only for low density population).
- Option 2 - night soil men collecting buckets and winching it to the top farming terraces.
- Option 3 - as above, but used for natural gas generation first
Urine is quite a useful industrial ingredient, so that might even be bought up.

Trash - same method used by all cities up to the industrial revolution. pile it up, pick it clean of useful stuff and burn it. (Ash itself can make a type of concrete, if you do it right. It's quite an easy discovery too.)

[Johonebesus]

Wouldn't it make more sense to give them cliff-cities, like the Anasazi or some Anatolian sites? They could have large chambers, corridors, and mines carved into the hills, even tapping into natural caves, but they would spend most of their time outside farming and herding. They could retreat into their tunnels and caves when attacked by humans, leaving men with the impression that they live deep underground. Legend could then exaggerate the size and depth of the subterranean chambers. There are some fantastic underground "cities" in Cappadocia, but even the largest ones were almost certainly used primarily as refuges. People might have dwelt in them long term, but much activity still happened outside.

I just don't see how giant cities built into mountains could work. In addition to the other problems already mentioned, wouldn't tectonic activity and weathering make them impossible to maintain? If you want more rational fantasy races, maybe you should back away from the clichés. As odd as it might seem, more mundane dwarves would actually be more unique and, to me, more interesting.

[madd0ct0r]

Whats the difference between a giant city built into a cliff face and a giant city built into the side of a mountain?

tectonics dosen't affect northern europe much and why would weatherng be a problem when you have a city full of dwarves?

[Johonebesus]

Whats the difference between a giant city built into a cliff face and a giant city built into the side of a mountain?

None, but what I was getting at was that it isn't at all practical to have an entire city completely underground. While you could have large underground chambers for storage, sleeping, ceremonies, and hiding, people would still spend most of their time above ground. That's why I brought up real world examples.

tectonics dosen't affect northern europe much and why would weatherng be a problem when you have a city full of dwarves?

Scandinavia actually does have a fair number of earthquakes. Any mountainous region is going to be near fault zones. Even the Appalachians occasionally get small tremors.

Weathering, tectonic activity, and other geologic processes are steadily destroying real underground cities. Think about it. If an earthquake knocks down some surface structures they can be rebuilt. But if underground structures carved from the living stone collapse, any repairs will necessarily enlarge and change the original chambers. If certain parts were essential for structural support, it might be impossible to recreate the original chamber. If the mountain is hollowed out, a combination of weathering and a good quake could cause the whole thing to collapse.

[madd0ct0r]

ok - your real world example had most of the population outside FARMING.

my example (which you don't seem to have read) had dwarves farming outside, forestry, and trading centers for dealing with other races. The forges, workshops, storage area and most industrial activity (so 70-80% of the population) are inside the mountain.
Problematic?

---

Tectonics:
Scandanavia gets frequent earthquakes? that i did not know. However, large parts of the UK, Germany, Switzerland and France manage to have large mountains with almost no earthquakes.

and I think the point is moot, since "if underground structures carved from the living stone collapse, any repairs will necessarily enlarge and change the original chambers. If certain parts were essential for structural support, it might be impossible to recreate the original chamber."
I agree. (i think you overestimate what an earthquake will do to a subterranean structure, but lets roll with this). So I have a large banquetng hall with other rooms running off it, and another floor opened up above it. Earthquake hits and the roof collapses.
Once the rubble has been cleared, I'll have a huge open high area. I'll need to put in large pillars to support the roof above it, probably with sensibly arch spans between them to share the load out.
hmmm. does this sound familiar?

[Sea Skimmer]

Spoil heaps - i think i touched on that in my post. Gravel goes for roads and concrete. A trading nation will have a vested interest in having good road access and it's an easy way to get rid of huge quantities of gravel. (maybe they used it to fill some of the natural chasms in Moria?)

Filling natural chasms might work very well if they exist and filling them doesn't cause floods; construction any distance from the mines is infeasible unless they had canals to ship the material, and even then it'd be pretty painful loading and unloading by hand. I suppose they might have structures to let them do the loading by gravity. Even today it’s very expensive to move aggregate any distance except by rail or barge. Given the indicated size of Moria, just moving the material within the tunnels would require a pretty massive effort. I suppose we might assume the flooding risk is minimal, because if the rock is wet this whole concept isn't going to work well. It'd be a constant rotting disease factory, well even more so then it would be no matter what.

Lighting - not something I'd really considered. I seem to recall dwarves having good night sight, so the problem is reduced in magnitude compared to humans. At the moment I'm going to go for oil lamps with later progression to gas lamps. I've found some sources claiming some mines used rotting fish for phosphorescent lighting in real life. Perhaps (yet another) use for the canals?
(fireflies are cute, but they don't really produce enough light, seen it myself)

Well, night vision is still dependent on the total light supply. Certain animals can see well in the dark because stars and the moon actually produce fairly large volumes of infrared light humans can't see. In a cave you don't have this hidden light to work with. Rotting fish is new to me, and a pretty awful idea from a sanitary standpoint. Early coal miners died like flies in any case.

. In some fiction I've been working on slowly, I toyed with the idea that Dwarves have some IR vision as well as simply using massive amounts of radium paint to light up less important areas, reducing the need for combustion based illumination. This would mean stuff like random trash tunnels could just have a few radium paint lines on the walls as directions. Its also part of the story that the Dwarves are highly resistant to radiation, allowing them to not all end up with cancer from doing this. If the Dwarves somehow knew to make it, you can make such paint with very basic technology.

Sewage
- option 1 - dump it in the canal (suitable only for low density population).
- Option 2 - night soil men collecting buckets and winching it to the top farming terraces.
- Option 3 - as above, but used for natural gas generation first
Urine is quite a useful industrial ingredient, so that might even be bought up.

Those might work, but they sure wouldn’t be popular or easy on labor. If they have a lot of big chasms, maybe they can fill them in with alternating layers of shit and gravel and pile on clay caps from time to time to try to lock in the gases.

Trash - same method used by all cities up to the industrial revolution. pile it up, pick it clean of useful stuff and burn it. (Ash itself can make a type of concrete, if you do it right. It's quite an easy discovery too.)

Cities in the industrial revolution usually did that that within the city limits; underground you just have this endless problem of constricted transportation. Sure you can make fly ash concrete, but one still has to haul the ash out of the mines, or else be hauling in cement. A pretty big fraction of Dwarven resources is going to have to go into transporting all this stuff in every direction, and the more animals they use the more air they need and the more food. This in turn would tend to favor more development on the surface or near surface rather then deep underground, raising more questions of why underground at all.

[Simon_Jester]

Whats the difference between a giant city built into a cliff face and a giant city built into the side of a mountain?

Number of times you personally have to swing a pickaxe during your life.

[Malagar]

Sewage
- option 1 - dump it in the canal (suitable only for low density population).
- Option 2 - night soil men collecting buckets and winching it to the top farming terraces.
- Option 3 - as above, but used for natural gas generation first
Urine is quite a useful industrial ingredient, so that might even be bought up.

Those might work, but they sure wouldn’t be popular or easy on labor. If they have a lot of big chasms, maybe they can fill them in with alternating layers of shit and gravel and pile on clay caps from time to time to try to lock in the gases.

How about mixing it with a good deal of water, store it in minor chasms/chambers, and then use wind power to pump it to the top of the mountain.
You could even use channels to distribute it to the individual fields.
If you have enough water available, then this would work well with roman style toilets.

Or am i overestimating the strength of wind power?

[Sea Skimmer]

I think the issue would be not wind power exactly, some powerful windmills can be made of wood and cloth, but rather transmitting that power. Basic belting and shafting systems are horrendously inefficient and not going to be able to function over distances measured in possibly thousands of meters. Even 18th century wooden and iron pumps are also going to leak in various manners and are not well suited to high continuous vertical lifts.

The best solution would be natural drainage of water and waste by gravity, if it were possible to cut a drain shaft of sufficient slope to a low enough point external to the mountain. Such gravity drains running for many kilometers might also act as miniature one way canals as a means of removing spoil using crude rafts or even just the flow itself to get rid of small debris, dirt and dust. But this would in turn be completely dependent on regional geography and the exact internal layout of the tunnels. It’d be a hard thing to have early in the life of the tunnel complex as well, so its not a way to explain how underground life as opposed to mere work got started.

[LaCroix]

They might have run into an underground cavern and river when digging their first shafts - usually, a settlement is done near a well. That well would come out of the mountain, and usually, flowing water would have dug a cavern into the rock - so they very likely would have started with an already existing cave (network?)

[madd0ct0r]

I've been thinking about this a little more, and came to the vague conclusion that Renaissance tech cities hadn't really solved the issue either.

I might try 'building' another few dwarfy cities, similar rules and emphasis on how each step is the logical one at the time - maybe one based in soft rock (salt cavern? coal mine?) and another craggy one but no canals this time

[Sea Skimmer]

A coal mine would be awful, you get far too much deadly gas and dust out of the coal seams. Digging into natural water worn caverns or wells also presents a massive problem of the tunnels forever being wet, cold and generally unsanitary. What you want is a large thickness of soft, consistent dry rock. Dry limestone would work pretty well; you can get dry limestone if it has a thick layer of harder impermeable rock above it. Chalks are also really, really easy to dig in though I dunno about tunnel stability within a mountain of chalk, if chalk can even make 'normal' mountains (no idea, likely possible). I can't think of anything above grade level bigger then the cliffs of Dover at the moment. If you had any coal involved in this, it should be in remote parts of the complex which can be very well isolated from the rest. You'd want not just air locks, but some kind of chicane system that will dampen the spread of blast of methane or coal dust explosions and direct it towards vent shafts. More then a few Dwarves might die to figure this out, and its not unlikely that even if the tunnels did once connect, all or the most direct connections would be back filled with barriers at least 40-60 feet thick.

Salt caverns would be easy to dig in, but then you have that pesky problem of your walls being easily dissolved. I don't think one normally finds mountains with major salt deposits because of this factor, if the salt seam reaches the surface it'd start being eroded in the rain rapidly. Things we've talked about like dumping your waste down a pit or digging canals for easy underground transport would be impossible or very risky. Coral makes for excellent easy to dig caves, and in the Pacific corals outcroppings can be hundreds of feet high but IIRC, coral is what turns into limestone in the long run.

The downside of soft rock tunnels BTW is its a lot more likely that you'd need to support the roof, and large span caverns could just be impossible depending on the thickness of the overhead cover. However near any rock will need extensive support if its to stand up for centuries. Since you can't have rock bolts before the 19th century this means archwork or support props, and only after you clear away and loose roof which in a large cavern could mean 40ft thick rocks falling down... keeping tunnels small really helps. Those movie Moria caves might actually be possible, but only if they had some vaulting on the ceiling I think. I have a file somewhere which suggested a unsupported 600ft diameter sphere deep underground is more or less plausible (purpose was to conceal underground nuclear tests, void space reduces the earth shock people detect) but this was to last only short term. I'll see if I can find that file again and what kinds of rock it was studying.

Also keep in mind its possible to tunnel in almost any rock with very basic tools using the fire method, build fire against wall, heat up rock, splash water on rock to crack it, but this would be very slow.

[madd0ct0r]

Vaulting - a given for any mining solution. It's a nice way to finish off the ceiling, and will provide a secondary protection layer. I'd also suggest that the dwarves develop the http://en.wikipedia.org/wiki/New_Austri ... ing_method relatively quickly, albeit probably not using steel props.

coal / salt: the logic was it operated as a large scale mine for a long time, opening up big areas underground. (both seem products with a large market in at the time. Chalk I'm not so sure about, although the dwarfs themselves would find it useful)

Once a large area had been mined out, then the space is put to use by the dwarf's moving in. I'm not for a minute suggesting they live in tunnels hacked into coal. Gas is certainly a problem, but since, unlike a classic mine, the tunnels would need to be well ventilated to be lived in, they might get away with it.
You are right that it would take a few goes and some dwarfs to get right.

Ventilation is the same thing I'd be looking at for improving the natural caverns. If you can divert the feeding streams / partially seal, partially channel infiltrating water you could probably bring the humidity down a touch. Certainly, I wouldn't see it as worse then the canal solution, as long as you have a constant air movement upwards through the mine.

I can actually see a way to do top-down construction using Renaissance tech, although I've not yet come up with a justification for it, unless the dwarves are contracted to build a tower/catherdral/huge monument and need to build hollow foundations for it. It's not really a stronghold then.

[Sea Skimmer]

Vaulting - a given for any mining solution. It's a nice way to finish off the ceiling, and will provide a secondary protection layer. I'd also suggest that the dwarves develop the http://en.wikipedia.org/wiki/New_Austri ... ing_method relatively quickly, albeit probably not using steel props.

Vaulting being so expensive and time consuming, I wouldn't really call it a given. It'd be used when it has to be used. Also since vaulting with stonework won't be water proof, it could actually make areas of wet tunnel more dangerous. It would help if the dwarves also have concrete technology. Not for structural use, but to use as waterproofing behind stonework. In real life that's actually how concrete in fortifications got started (at least in the modern era, no idea on Rome) it was used to waterproof the external surfaces of masonry used on British coastal forts in the 1860s. Concrete is not totally waterproof either, but it can help mitigate the spread, and direct it towards easier paths into drains.

coal / salt: the logic was it operated as a large scale mine for a long time, opening up big areas underground. (both seem products with a large market in at the time. Chalk I'm not so sure about, although the dwarfs themselves would find it useful)

The problem with this idea is that normally when people mine for a product, they dig out only exactly the space needed to get out the desired material. With salt that isn't so big an idea, since the seams tend to be very thick, but with coal it often leads to very oddly shaped tunnels. Converting them into safe useful space can be very resource consuming. Chalk, well its simply very easy to dig into. Two Dwarf's with a pick and shovel could dig multiple feet per day as long as the ones behind them can keep up with removing the debris. It would help to have some kind of pack animal which is no taller then the tunnels, so not a mule or donkey as we know it, to help haul away stuff. Normal tunnels should would be taller then Dwarfs to provide better venting ect.. but I doubt they'd be human height. After all keeping them small, at least until deep into the mountain would also provide a defensive advantage.

Also random thought, the Dwarfs would want to dig emergency exits that are say 15-20 or so feet short of breaking out of the surface. Thick enough that someone on the surface digging himself a hole for some random purpose would not break into the tunnel, but thin enough that the exit can be quickly opened in the event of a attack/flood/fire

Once a large area had been mined out, then the space is put to use by the dwarf's moving in. I'm not for a minute suggesting they live in tunnels hacked into coal. Gas is certainly a problem, but since, unlike a classic mine, the tunnels would need to be well ventilated to be lived in, they might get away with it.
You are right that it would take a few goes and some dwarfs to get right.

The ventilation you need to keep down gas and dust in a coal mine is much higher then what would be needed to simply support human life and keep the air dry. Coal mines normally wall off all unused shafts so they can avoid ventilating them. Some exposure to coal would be acceptable I imagine, if you had the airflow rigged the right way so the air from the coal area is never drawn into other parts of the complex, but converting a whole coal mine is a non starter.

Ventilation is the same thing I'd be looking at for improving the natural caverns. If you can divert the feeding streams / partially seal, partially channel infiltrating water you could probably bring the humidity down a touch. Certainly, I wouldn't see it as worse then the canal solution, as long as you have a constant air movement upwards through the mine.

Water that is already flowing in streams or what have you isn't such a killer for humidity as surface area is limited. The worst problem is the seeps out of the walls making the walls and roof constantly wet. Lots of surface area like that turns into lots of humidity, and the water is not easily collected and drained away. Even today this is a problem. But like I was saying above, wrote this reply patchwork like, if you had concrete held against the wall with masonry you could have some hope of directing the water into drains. But this still means the drains have to go out of the mountain somehow. That's when a canal system would be handy, since frankly I'd rather not rely on diverting water and waste into natural channels which may increase erosion with completely unknown effects on the stability of the cave system. That could mean stuff collapses, with the risk that a roof fall in the water channel could turn into a dam, causing a flood.

I can actually see a way to do top-down construction using Renaissance tech, although I've not yet come up with a justification for it, unless the dwarves are contracted to build a tower/catherdral/huge monument and need to build hollow foundations for it. It's not really a stronghold then.

Top down, you mean like cut and cover? I was thinking cut and cover would be a lot better for underground living then tunnels, but it certainly would be very expensive. The stronghold nature would depend on just how thick the overhead cover was and if you can expect external help to drive away an enemy before he digs through. Good enough stone vaulting could support a damn lot of rubble, but then you have to move all that rubble back and forth. Of course, it is worth considering that if you have tunnels into soft rock, then its totally plausible that an enemy will dig his own tunnels to invade anyway. You also have the endless problem of the enemy diverting water into your stronghold, if possible, and blocking up air shafts will always be a threat, though if they are high enough up in the mountains they could be very difficult for an attacker to reach with the approaches and vent structures fortified in positions in which the enemy cannot bring siege engines of any great size against them.

You might be interested BTW, a while ago I obtained some Ebooks via certain sources you might want which deal with extensive British efforts to convert underground quarries into magazines and factories in the 1930s-WW2 which touch on a lot of unexpected problems with conversions, such as floors not being leveled, impossible water problems (within the budget anyway) as well as cut and cover construction you might be interested in. The overall technology was far more advanced of course, but many of the solutions were actually nothing very high tech, just very time and money consuming. Also several of them collapsed, and one exploded when someone used the wrong hammer on a stack of fused 4,000lb bombs. None of the facilities though was really into a mountain, most had more like 100 feet of overhead cover which created stability issues in some cases once the best sites had all been taken.