Stewart Brand in an article about the Ten Thousand Year Clock
Many of the best preserved artefacts probably spent most of their time underground. The subterranean environment protects them from sunlight and generally keeps a very stable temperature. The rise and fall of temperature accelerates oxidation and aging. In fact, when manufacturers do rapid aging tests for materials, it is done largely through cycling temperatures up and down (and chemical effects, which we will get to next).
The ornate tombs of Luxor, Egypt, cave paintings such as Lascaux in the Les Eyzies valley of the Dordogne in southwestern France, and even delicate artefacts such as the Dead Sea Scrolls were all preserved underground for thousands of years. It is no wonder that modern efforts of preservation such as the Global Seed Vault, nuclear waste repositories and archives are all built beneath the surface.
If we want people to voluntarily rewild, then providing long-lasting basic infrastructure – food, clothing, water and shelter – will be paramount. Because climate can vary substantially, especially if you allow for major volcanoes eruptions, then living underground has a lot of appeal. It has a more stable temperature and less need for heating or cooling.
Also, although there are some potential issues with being below ground, like moisture, a major advantage is that there is no wear and tear or erosion from wind, rain, animals and plants. In theory an underground house could be built which will last tens of thousands of years.
Most online experts seem to think that concrete is not up to the task, for the construction layer in contact with soil. But we do know from ancient structures that stone and ceramics can last thousands of years. Just look at the pyramids… Possibly steel could be used to take the load of the roof and soil above, with the outer layer could be made of an artificial medium, like epoxy. PET plastic can take 450 years to degrade, and plastic bags 1,000 years. That is not long enough for us. Stone however is literally designed to last in that environment, and glass will never degrade (but of course can be broken if thin enough).
Two inch thick structural glass can be manufactured at any size you want, so a “bunker” with four sides would only have 4 joins that need to be dealt with. Even with perfect alignment, and plastic coatings, eventually moisture would get through, so that needs to be addressed.
The load bearing walls could be a combination of, or one each of (for redundancy):
- 2 inch thick structural glass
- stone
- non-reinforced concrete, sandwiched in-between
- epoxy covered steel
Epoxy could be used for all joins and gaps. Perhaps add some layers of different plastic sheets on the very outside, for longer protection. Even carbon fibre sheeting.
The roof needs to be lightweight, considering it will have a depth of earth on top of it. Being waterproof is of course a priority, and the design needs to allow for water to run off. This is perhaps the hardest part to get right, but the good news is that is the easiest for a non-technological people to repair if the walls remain.
The good news is that intention is not the same as a survival bunker, which is usually made with protection from radiation and bad people in mind. The design I am imagining is not going to have any pumps or ventilation systems, and no thick steel doors.
The primary purposes of the “bunker” are:
- Somewhere to sleep
- Stay out of the elements / heat / cold
- Storage of food and other valuables
In general toilets, cooking and water gathering all occur outside, when it is convenient. Even in scorching weather, it is cooler at night. Even in the depths of winter, going outside briefly is just fine with sufficient clothing.
Farming is a different matter, and similar structures to the home could be built to effectively create greenhouses for extremes of weather. The design would not include plastic sheeting or glass… See The Earth-Sheltered Solar Greenhouse Book
For siting, ideally it is built into a natural hill. A deep rectangular pit is dug out, the structure built, and then covered back over with soil and grass. A tunnel goes down from the building to the external slope. It needs a gentle slope for when any stairs fail. The tunnel is also where any water exits. In a worst case scenario, the roof can be replaced with timber and organic materials, and even if it wasn’t completely waterproof it would still be ok, as water can drain out.
Two entrance tunnels, for redundancy. Where they reach the outside world needs some significant structural attention, the equal of inside, to protect the area from erosion. A thousand years of erosion. The tunnels need to have a relative size sufficient for air to recycle. Any doors should be organic and permeable like wood or skin. With sufficient space and multiple points where very thick doors could be added at any time. Possibly ventilation shafts could be used but that could be a temperature issue. If they did exist, then that could also mean that smoke could escape. Possibly the structure has multiple rooms, each with their own external tunnels, and internal tunnels linking them. That way there is more air circulation, and storage, cooking and sleeping could be separate.
By not having systems – heating, cooling, waste, air – the design becomes simple and costs low. For approval from the authorities, the lack of such systems could be enough to convince them it is simply a storage facility.
A negative that needs to be addressed is lighting. All primitive lighting uses fire. Skylights would mean exposure to the elements. Steel mirrors could provide enough light, and kept rust free long-term. The directions of the tunnels would ideally match the rising or setting sun. Or both! But of course, those vary throughout the year.
Light becomes an issue when the structure is large and the tunnel is long and narrow. While these are good for thermal reasons, we could consider other shapes and sizes as well. A much smaller structure, suitable for just 1-2 people, and with a short tunnel, could be used for anything that needs the most light – a living room if you want. There could be many of those in a row, like terraced housing with shared walls, used as bedroom/living areas. While the main structure could still be used for very bad weather, the little hobbit homes could be used at other times and designed so that replacing the roofing was easy.