That’s a solid idea, but it’s a chess match with the codes. First, you’ll want to check the local building code for wind load—those tables in Section 16.3 will tell you the required gage for a storm shelter, and the fine print about egress windows. Next, the “green” angle: you can’t just slap a green sticker on anything. If you’re using recycled steel, you need to prove the material came from a certified source; the certificate of compliance has to be on file. For concrete, look at the embodied carbon numbers—there’s a whole clause about using supplementary cementitious materials like fly ash. Then there’s the safety code: you’ll need a structural engineer to submit a design that meets the seismic and wind criteria, and the fire department will want to see a fire-resistance rating. If you use timber, be sure it’s seasoned per the fire code’s ASTM standard. And don’t forget the egress requirements—two exits, a maximum of 1.2 meters to the exit, and the fire-rated doors must meet the 60‑minute standard. The rainwater collection spreadsheet I keep on my spreadsheet: it can help you design a catchment system that feeds the shelter’s potable water needs during an emergency. Just make sure you reference the local potable water regulations; the fine print says the catchment must be a separate system with a minimum 2‑meter pipe to the storage tanks. If you can get a single‑story, reinforced concrete structure that uses recycled aggregates, meets those wind tables, and passes the fire rating, you’ll have a shelter that’s both storm‑ready and truly green. Keep an eye on the “green‑washing” clauses—those are where people lose the point.