I've been planing a earth roof my cabin next year. I want it to be as light as possible and still function. As I understand it, the thinner you go on earth the less able the vegetation is able to survive drought.
This morning it hit me. What if I used a bunch of wood chips for a base layer and got the water retention benefits of hugelkulture? (I know water is not light)
I might second the charcoal recommendation, and add: even if it's absorbed in something very lightweight, enough water for intensive plant growth is going to be extremely heavy.
Since you're designing and building this all on your own, might I recommend very shallow soil where it will be difficult to support, and very deep soil where it will be easy? Often walls will be able to support tons in addition to the roof, but soil should be spread thin over long spans. Vegetation can still be thick over the whole roof, if it vines out from the intensive planter beds, and a low-maintenance groundcover remains as an understory.
"the qualities of these bacteria, like the heat of the sun, electricity, or the qualities of metals, are part of the storehouse of knowledge of all men. They are manifestations of the laws of nature, free to all men and reserved exclusively to none." SCOTUS, Funk Bros. Seed Co. v. Kale Inoculant Co.
posted 10 years ago
timber is ideal, steel is great- if you are using conventional framing I would pair 2X12s at 14 or so OC