One thing the game does not make super obvious is that if a room is built out of a mountain it will naturally try to climatize towards 18-21 Celsius. Does not make a huge difference normally but in those extremes it can be a life saver.
I'll be posting a good tip for mountain building--OTHER THAN the
unmentioned note that you get Insect Infestations if you build your living area under Overhead Mountain as the 'roof tile' (pros and cons; impervious to mortars/shelling, climate 'stability', can't drop-pod in either by trade ships or your own, and can't remove so it acts like a permanent roof that you've to support), there's also the note of it being a permanent roof in that if you have a fire in there that starts inside that spreads without anything good to stop 'mass fire', and you've well insulated the place, you're doomed unless you use less flammable material internally.
I had a colony wherein I just wondered how it'd go if I left my folks away for a bit--that's how I discovered the 'non-smart AI' as a simple fire that occurred by 'raid drop pod' (which sparked a fire as I had a tiny valley stretching into the heart of the mountain which had them drop
right there in the heart of my base) turned into a blazing inferno, with temperatures reaching 200+C in a Boreal Forest of ~-40C because I played with the Rimsenal Federation mod that had 'explosive scouts that are useless and don't even melee well'. (On the scout note, those 'creatures' just melee for 1 second, and take a minute to reset. They just freeze and do nothing)
Anyway the lack of firefoam (because it was 'ugly') and my plasteel internal walls due to my richness had me intrigued and wonder if I turned up the notch--Devmoded in Infestations; apparently this also unveils another layer of 'non-smart AI' (basically meaning "more basic AI" just like how DF was very, extremely early on): Pawns/Characters can't rescue at will. Or they can but despite the high priority there's a lot that can skew it >_> They don't auto-attack Hives once an area is cleared of insects, and in a regular mid/end-game, normal unarmed people will usually
not even die because insect attacks/scratch or bites usually result in more pain over damage (even with the "soldier" Megaspiders which lovely aren't stupid spiders in lore, description, or imagery, so I can FINALLY PLAY A GAME THAT DOESN'T HAVE DAMNED SPIDERS UNLIKE TERRARIA). Playtesting it out, 1 our of 12 of my colonists were killed...because of friendly fire in using the Rimsenal Jotun Interstellar corps. AMR gun. One shot my colonist through the chest--40 hp of that part versus the 55 damage armor piercing shots. <_<
And the insects just 'randomly mine'. So compared to the overall integrity of even a plasteel wall, it goes down
extremely easily if you've either "insects that mine" or "wild animals trapped inside". [I had luckily gotten a Megasloth downed and planned to train it to haul given its 97% wildness...or at least be a training puppet for my folks' animal score so I can aim for Thrumbos. This one wild beast 'mined' itself out after no food for quite some time, just knocking down plasteel autodoors
like they were nothing compared to insects attacking it?!]
Thrumbos aren't even that good in combat (as I downloaded a mod that makes them trainable, tameable [90% wildness], and has Thrumbo wool), as they have the usual 'slow melee cooldown' that doesn't seem to be influenced by ANYTHING other than the stat condition in making the game scenario, and the item modifier that is the
attacking item itself compared to the modifiers armor can give. They can be overwhelmed despite having ~200+ base hp for the appendages and 500+ for the torso...and I had kit'd out my thrumbos in bionics! (Armor stat modifiers can influence ranged combat, but melee combat seems tied to only the weapon having a melee DPS modifier given both its wording and devmode checking :/)
...That wall of haphazard text aside, back on the idea of 'internal fire system', the fire spread as all my colonists were downed and I had drop pod'd the last one for safety and non-game ending reasons. In any range of 10+ that makes travel time being a day or more, it's better to 'settle' and make your own drop pod back, as scenarios like these even with internal plasteel walls/doors, it'll burn down within a day. This was my internal colony size of 300x300+. (Imagine at least the maximum scroll box of selection multiplied by 1.5). It burned down slowly, invoking feelings of watching a piece of hard work crumble into decay and disrepair. Bodies rotted, and at the end when the outer 'temperature seals' (walls) were breached, it still burned down at -20C + temperatures with no difference in speed.
This game needs better stuff than firefoam if you're stuck in a mountain.