From time to time we answer reader’s questions.
Q: Why aren’t people making roofs from earth using domes or Nubian vaults? In impoverished areas the cost of a tin roof is sometimes a year’s salary.
A: Domes and vaults evolved in extremely dry areas of the Middle East, where wood was scarce and lack of rainfall wouldn’t destroy the earthen roofs. People are often captivated by the unique look of domes and vaults and want to build them in other climates. Earthbag building extends the possibilities beyond desert regions, yet still domes and vaults are somewhat vulnerable to moisture problems, and so if this is your plan then you’ll want to design and build them very carefully. Options include using cement stabilized soil or waterproof materials such as lava rock as fill material, cement plaster and elastomeric roof coating. Also, eyebrows over doors and windows are recommended to provide extra protection for these areas. Building a roofed dome is probably the best option in rainy climates.
So yes, wood roofs/metal roofing are costly, but you can see that domes and vaults also have costs: cement for stabilized soil, cement plaster, roof coating, eyebrows. There’s no free lunch unless you want to live in a grass hut or something. Plus, earthbag vaults are tricky to build and therefore limited to small spans.