CS
Complete Build Plans
Steel-Framed Trailer Cabins · 40ft Container Homes
The full CargoSolar build set: cut lists, assemblies, budgets, and build order for a solid steel-framed cabin on a trailer frame and a 40-foot container home — built to sit, dried in first, finished out on your schedule.
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Contents
What's Inside
- How To Use This Plan Set
- Plan A — Steel Cabin on an 8×12 Trailer Frame
- Plan B — 40ft Container Home
- Solar Sizing Quick Reference
- Master Materials & Tools Checklist
- Build-Day Checklist
How to use this: Print it, or keep it on a tablet at the build site. Every cut list is per unit — multiply by however many you're building. Build all your shells to dried-in first, then finish out one at a time. Prices are material targets, not store quotes; confirm local pricing and code before you order.
Plan A
Steel Cabin on an 8×12 Trailer Frame
A solid, stationary metal-stud cabin on a used trailer frame. The floor decks up over the wheels for a flat 8-ft-wide interior, with an enclosed storage bay underneath. Built to sit — ignore the running gear beyond an occasional slow tow.
Framing Spec
- Walls: 3⅝″ steel studs, 20-gauge minimum, 16″ on center, in matching steel track.
- Roof: 6″/8″ steel joists as rafters, 16″ OC, on a 2:12 shed slope.
- Screws: #8 self-drilling framing screws; #10 at high-load joints.
- Thermal break: 1–2″ continuous exterior rigid foam over the studs before siding (steel telegraphs cold — this is mandatory).
- Corrosion: galvanized studs/track; keep steel out of standing water.
Assembly Stack-Ups (inside → out)
- Floor (raised over wheels): coated frame → sill membrane → risers to clear tires → joists 16″ OC → 3/4″ T&G plywood. The gap is the belly storage.
- Wall: interior panel → steel studs + batt → sheathing → housewrap → continuous foam → furring → metal siding.
- Roof: ceiling panel → steel rafters + batt → sheathing → underlayment → standing-seam/corrugated metal on a shed slope with overhang.
Cut List (Per Unit)
| Member | Cut / Size | Qty |
|---|
| Steel framing — 3⅝″ 20-ga studs, 6″ joists |
| Long-wall studs, high eave | 8′4″ | 10 |
| Long-wall studs, low eave | 7′0″ | 10 |
| End-wall studs (raked) | 7′0″–8′4″ | 10 |
| King/jack at openings | wall height | 8 |
| Wall track (top+bottom) | 10′ sticks | 8 |
| Headers (door + 2 windows) | boxed | 3 |
| Roof rafters | 9′0″ | 10 |
| Floor joists | 8′0″ | 10 |
| Floor risers | per frame | ~14 |
| Skin & dry-in |
| 3/4″ T&G subfloor | 4×8 | 3 |
| Wall/roof sheathing | 4×8 | 13 |
| Rigid foam | 4×8 | 10 |
| Metal roof panels | 3′×9′ | 5 |
| Metal siding | ~400 sq ft | 1 lot |
| Door + windows | 32″×80″ + 2 | 3 |
| Framing screws | bulk | ~1,500 |
Budget (Per Unit)
| Phase | Item | $ |
|---|
| Phase 1 — Dried-in shell (~$4,750) |
| Frame | Prep, level, coat, jacks | 350 |
| Floor | Risers, joists, subfloor | 650 |
| Storage | Belly bay + hatches | 300 |
| Steel | Studs, track, fasteners | 1,150 |
| Envelope | Foam, WRB, flashing | 700 |
| Cladding | Metal siding + roof | 1,100 |
| Openings | Door + windows | 500 |
| Phase 2 — Finish-out (~$3,150) |
| Interior | Insulation, panels, floor | 850 |
| Wet bath | Pan, FRP, toilet, fan | 650 |
| Kitchen | Sink, pump, plumbing | 350 |
| Electrical | Shore, GFCI, lights | 450 |
| Appliances | Fridge, micro, AC | 400 |
| Buffer | Paint, trim, mistakes | 450 |
| Total | Complete, per unit | ~7,900 |
Build Order
- Prototype shell first — build one completely, then repeat.
- Prep & level the frame; set sill and barrier.
- Raise the floor over the wheels; frame & skin the storage bay before decking.
- Stand the steel walls; box every opening.
- Frame the shed roof with overhang.
- Set door & windows.
- Dry it in: sheathing, WRB, foam, metal roof, metal siding. Repeat 2–7 on all frames.
- Finish out one at a time; final level, anchor, tie down.
Plan B
40ft Container Home
One 40-foot high-cube container per unit, set permanently on piers. Spray-foam the steel, frame the interior in metal studs, weld reinforcement around every cut, and run the same plan across each shell.
Key Spec
- Foundation: concrete piers or blocks under corner castings + mid-span, dead level. No full slab required.
- Insulation: closed-cell spray foam on the interior steel skin, 2″ minimum — the real condensation fix.
- Interior framing: steel studs for partitions and the service wall, furred off the foam.
- Cuts: weld steel tube/angle around every door and window before moving on; keep openings modest.
Budget (Per Container)
| Category | Target | Notes |
|---|
| Container + delivery | $4,500 | Used 40' HC |
| Foundation / piers | $1,500 | Level base |
| Cut + reinforce | $3,500 | Steel around openings |
| Spray foam + framing | $4,000 | 2″ closed-cell + studs |
| Windows + doors | $3,000 | Door, windows, flashing |
| Electrical | $2,500 | Panel, wire, fixtures |
| Plumbing + bath | $4,500 | Shower, toilet, heater |
| Kitchen + appliances | $3,000 | Sink, fridge, cabinets |
| Flooring + finish | $2,500 | Durable interior |
| HVAC | $2,500 | Mini-split or window AC |
| Contingency | $3,500 | Hardware, sealants, misc |
| Total | ~$31,500 | Serious DIY low end |
Build Order
- Buy the right shell — inspect floor, corrosion, roof, confirm it's a high cube.
- Set & level on piers before cutting.
- Cut and reinforce — frame every opening immediately.
- Spray foam, then frame interior partitions and service wall.
- Run electrical, plumbing, venting, HVAC support.
- Finish, seal, test for leaks, then live in it before upgrading anything cosmetic.
Three-container note: prove container #1 fully, then repeat. One delivery and bulk foam/steel/finish orders across three usually save 8–12% — budget about $85,000 for three complete.
Bonus
Solar Sizing Quick Reference
Off-grid sizing rule of thumb. Solar is a second phase — get the shell dry and usable on shore power first, then add panels, a battery bank, and an inverter.
| Use case | System | Battery | Parts est. |
|---|
| Lights + phone + fan | 1–2 kW | 2–5 kWh | ~$3–6K |
| + Fridge + small AC | 3–4 kW | 5–10 kWh | ~$8–12K |
| Full off-grid living | 6–8 kW | 10–15 kWh | ~$14–20K |
- Panels: roof-mount on the shed slope facing the sun; leave an air gap.
- Battery: LiFePO4 is the durable choice; keep it inside/insulated.
- Inverter: size to your peak load, not average — AC startup is the spike.
- Shore-power first: wire a 120V inlet + GFCI now; solar plugs into the same panel later.
Bonus
Master Materials & Tools Checklist
Structure & shell
20-ga steel studs + track · 6″ joists · #8 self-drilling screws · 3/4″ T&G plywood · construction adhesive · rigid foam · housewrap · butyl/flashing tape · metal siding · metal roof panels + closures · batt insulation · steel door · windows
Systems (finish-out)
Shower pan + FRP · cassette/composting toilet · exhaust fan · bar/kitchen sink + faucet · 12V pump · water + gray tanks · shore inlet + GFCI + breaker panel · LED lights + wire + bushings · mini fridge · microwave · window AC or mini-split
Tools
Impact driver + framing bits · aviation snips / metal shears · chop saw with metal blade · drill · rivet gun · level (4′ + torpedo) · speed square · tape · clamps · caulk gun · PPE (gloves, glasses, ear) · jack stands · ladder
Bonus
Build-Day Checklist
- Frame level and non-rocking on stands? ☐
- Steel-to-wood contact isolated with membrane? ☐
- Belly storage framed & skinned before decking? ☐
- Every wall opening boxed with double studs + header? ☐
- Wire pass-throughs have bushings/grommets? ☐
- Continuous exterior foam on before siding? ☐
- Roof slope, overhang, and drip edge correct? ☐
- Water-tight (WRB, flashing, roof) before any interior work? ☐
- Window AC verified not a recalled Midea U/U+? ☐
- Ground anchors + tie-downs set for wind? ☐
Questions on your specific frames or containers? The live guides at CargoSolar.com stay updated — and the cost calculator will re-price any change in size, finish, or solar.