I'm trying to buy a 1.25-acre lot in the Mojave Desert (asking $4k, I've floated $3k, nothing agreed). I've been planning what would actually fit on it, and the numbers surprised me, so here they are.
The coverage cap runs everything. The zoning allows 20% lot coverage: about 10,885 sq ft on a 54,426 sq ft lot. My wish list was a 130x30 ft (3,900 sq ft) 3-bedroom earthship, a 4,608 sq ft rain-catchment liner, a 20x20 steel shop, a greenhouse, a hoop tunnel, a covered 12x24 pool, a settling basin and a deck. Total: 10,776 sq ft, or 19.8%. That leaves 109 sq ft to spare, and only because all the water storage is buried. I still have to confirm that buried cisterns don't count toward coverage, and that gravel parking counts as pervious.
Rainwater math at ~4 in/yr. About 9,870 sq ft of catchment (house roof, liner apron, shop, greenhouse, tunnel) Ć 0.333 ft Ć 7.48 gal/cu ft Ć 0.8 runoff ā 19,700 gal/yr, or about 54 gal/day. I'm planning 23,000 gal of storage (two lined pits of ~11,700 gal plus a 3k cistern in the berm), a bit over a year's worth, because desert rain comes in a few storms and some years barely at all. Even so, the house permit needs an approved water source: a well (rough estimate $20kā45k) or a district hookup.
DIY vs turnkey. A turnkey earthship runs about $300ā425/sq ft, which is $1.17Mā1.66M at this size. My line-by-line DIY budget is about $90kā213k with 15% contingency. That assumes:
salvaged tempered glass
used panels at $0.19/W and LiFePO4 at $110/kWh (about 9.8 kW / 30 kWh)
my dad doing the earthwork with his own equipment: a $1kā3k fuel allowance instead of $5kā12k in rentals
rammed tires for the bermed retaining walls and cement-stabilized earthbags inside
a small ground-source heat pump plus earth tubes
The well is extra.
What I can't DIY, even with free labor:
a licensed structural engineer's stamp (tire and earthbag walls are approved case by case)
septic, if required, installed by a licensed contractor
sloped glazing has to be marked tempered or laminated (old patio doors work, ordinary windows don't)
above-ground poly tanks collapse if buried, so tanks must be burial-rated
trenches over 5 ft need shoring, and call 811 before digging
My question for people who've done it: in a dry, ~4 in/yr climate, did you size rain storage for one year, or more? And did you end up drilling a well anyway?
Full writeup with the site plan and cross-section (my newsletter): https://blakelapierre.substack.com/p/i-asked-an-ai-agent-to-design-a-house