Having worked in construction and a bit in building science, there is a single major problem with subterranean construction: Water. Diffusion/osmosis means th

Having worked in construction and a bit in building science, there is a single major problem with subterranean construction: Water. Diffusion/osmosis means that moisture is going to want to go from high to lower concentrations. Untreated poured concrete is permeable and will allow water to seep through if installed without any sort of vapor barrier. There are building products to help out here, but it’s difficult to identify leaks if you are only leaking a 0.1oz of water per day, it evaporates faster than you can identify it. Once it has some refuge (humid air, damp environment, porous surfaces) it will begin to accumulate and cause problems. I’m not saying it’s not impossible (I think under ground stuff is cool and we should have more of it), but we need to develop standard, cheap methods of reliably sealing off our structures that reach down below. There are other problems that are site-specific (sandy soils, clays, bedrock), but building below grade happens once so these problems can be overcome with enough money.