I used to be in the home-building industry... With a team of three carpenters a hand-saw and hammers I could build a house like the one in the picture in 48 ho

I used to be in the home-building industry... With a team of three carpenters a hand-saw and hammers I could build a house like the one in the picture in 48 hours out of a sustainable material - softwood. With a nailgun I could go quicker still. I could use a 4x2 studding wall, plywood, breather membrane, counter-batten, clad with larch featheredge. Once up a vapour barrier could stapled inside and recycled paper insulation blown in. Inside that I could line out with fire resistant plasterboard (drywall to my transatlantic cousins) (backed with urethane if extra insulation is needed). This design is easily prefabricated if desired. To contrast with the concrete one this would a) use sustainable materials b) meet the building code of a developed nation. If you are dead set on a concrete wall then just build a set of plywood forms (shuttering as it was called in my day) and cast it in place. A day to put the forms up and pour. The forms are reusable too once set. Now you have a bunker to insulate, waterproof and line out. In the UK you would need to build some kind of studding inside your pill-box for insulation and damp control, much like the 'barn-conversions' the UK is full of. This makes the concrete bit semi-redundant. Sorry but I think this is a poor application of 3d printing. All we need now is a start-up to build a house with a cloud-based block-chain to get the VC's really excited. If you want to look at some really quick constructions there are the brilliant post war 'pre-fabs' of the UK, designed to replace housing lost to bombing. Some could be assembled on-site in 4 hours! There are many still in use today. If it wasn't for the amount of asbestos used there may have been many more still remaining. https://en.wikipedia.org/wiki/Prefabs_in_the_United_Kingdom https://en.wikipedia.org/wiki/Prefabs_in_the_United_Kingdom