When I built the house I just spent 7 years working on, I had a lot of days that were just plane monotonous, so I would daydream about the Next Great Project as soon as I finished the house...
If you're OCD you know exactly what I am speaking about.
Perhaps it was watching too many reruns of Stollag 17...
Maybe it was all the Underground cabins we built as kids to have a cool place to hide out in the summer.
Truthfully though I just love to build things and when I designed the house I made the bottom level only half the size of the main floor and the other half is a crawlspace about 4 foot high.
Most of my plumbing and stuff runs around the floor joists down there so I wanted enough room to have access to everything but I didn't want to build an eight foot wall, It took me 7 weeks to do the block for the garage workshop and storage room so saving 4 feet of wall seemed like a good idea.
Looking back if I really intended to do this and had the wife's permission I could have saved a lot of bother by doing this first and I wouldn't have to worry about the house falling on my if I dug out too much from below it.
I didn't leave any vents to the outside mostly cause of wanting to be energy efficient and not have a cold room under one above I was trying to heat in winter. I did talk to the building inspector about this and convinced him I could put a gable vent fan on a timer at each end one blowing in and the other blowing out to ensure a good change of air so it never mildews. I intentionally made it to push air into my workshop and draw replacement air under the house at the far end of the garage. This way in the winter when I am using the wood burner if I am working on something I can open the duct to the workshop and close the damper and the heat travels in a big circle across the garage into the crawlspace and then back into the workshop to circulate the heat so I can work on something midwinter if it is 40 out with a t-shirt on.
I got lost in a Blizzard when I was abut 20 for 23 hours and was 31 miles from where we parked when found, so I don't do cold anymore...
When I laid out the supports to the crawlspace I left a wider gap between two of the columns supporting a beam since the crawlspace is 20 foot wide and I didn't want to pay to special order 20 foot 2 by 12's and I just happened to have gotten a deal on a couple 40 foot beams delivered by accident to my house and unloaded before we discovered they loaded the wrong ones and were two thin to support the bottom garage ceiling. They sold me them to me at cost when they delivered the proper beams a few days later because it would have cost them money to rent a piece of equipment to lift them back on the truck.
I also filled the back of the bottom garage wall wide enough for a ten foot door and didn't put any rebar in that section. All the rest of the bottom level block has rebar in ever other hole and is filled to the top with concrete instead of just every 4 feet as code calls for. I will be able to saw this opening or get some of that ACME black paint they use to make tunnels and then start digging with a bobcat and dumping the dirt on the slope behind the pool so its not as steep a grade since I use a push mower for the exercise.