🥶

The Veggie Cold Box

Proposal: a wood-framed, XPS-insulated walk-in cold box with dual AC cooling — built like a real cold room, reusable for years.

✅ APPROVED · doing both: fridges + box · 12-step visual build guide →

TL;DR

Build a plywood box with XPS foam glued + screwed inside — structural skin outside, insulation inside, exactly how commercial walk-in coolers are made. Our two 5,000 BTU ACs mount in wood-framed openings instead of hanging in tape-sealed foam holes. Real door with hinges and a latch. Rides to BRC fully assembled in the semi.

Cost: ~$320 over the foam-only build · ~1 build day at the Gulch · reusable for future burns.

Why change? The original tape-hinge folding design existed to fold flat for transport. We now have a 53' semi — transport volume is a non-issue. That frees us to build the stronger, more usable, more durable version.

1 · The Design

            ~8' 6" (outer)
  ┌──────────────────────────────┐
  │  ply roof, slight slope, white│   SIDE VIEW
  ├──────────────────────────────┤
  │ ╔══════════════════════════╗ │
  │ ║ 3" XPS in every wall bay ║ │  ~4' 6"
  │ ║                          ║ │  outer
  │ ║ [AC LOW]        [AC HIGH]║ │  height
  │ ╚══════════════════════════╝ │
  ├──────────────────────────────┤
  │ 2×4 skid base — air gap under │
  └──┬────┬────────────┬────┬───┘
     ▓▓   ▓▓           ▓▓   ▓▓   ← skids on blocks


       TOP VIEW (~8'6" × 4'6" outer / 8'0" × 4'0" inner)
  ┌───────────────────────────────┐
  │ ▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒│ ▒ = 3" XPS
  │ ▒                           ▒ │
  │ ▒   wire shelving + crates  ▒ │◄─ DOOR (end wall,
  │ ▒                           ▒ │   hinged ply+XPS)
  │ ▒▒▒▒▒▒▒[AC1]▒▒▒▒▒▒[AC2]▒▒▒▒▒▒│
  └───────────────────────────────┘
        ACs on the SHADED long side
Footprint ~8'6"×4'6", interior ~8'×4'×4' high (≈128 cu ft usable). Same footprint as the original plan.
  • Frame: 2×4 skid base + 2×2 wall studs at corners and AC openings. Everything screws into wood, not foam.
  • Skin: ½" CDX plywood outside (¾" for the floor deck). Painted white / roof wrapped in spare Aluminet.
  • Insulation: the 3" Dow Scoreboard XPS we already own — friction-fit into bays, foam-safe adhesive + screws with fender washers. R-15 walls.
  • Cooling: 2× COWSAR 5,000 BTU 115V window ACs (✅ received, manual controls per David) in framed, flashed openings — one mounted LOW, one HIGH for circulation. Both on the shaded side.
  • Door: ply + XPS sandwich on gate hinges, foam weatherstrip, gate latch + pull handle. Opens outward.
  • Base: raised on skids → air gap kills ground heat-soak, and the box can be dragged/forklifted.
  • Target temp: ~50°F for produce (not a fridge — a produce room). Min/max thermometer inside, logged at kitchen open.

2 · Why Wood + XPS Beats the Tape Yurt

✅ Wood + XPS box (proposed)

  • AC bolts into a wood-framed opening — what window ACs are designed for
  • Screws + glue survive playa heat; no adhesive failure mode
  • Real door — opens 20×/day during kitchen service without re-taping
  • XPS fire + UV weaknesses hidden behind plywood
  • Reusable — burns 2027, 2028… or gulch cold storage off-season
  • Rides assembled in the semi (8'6"×4'6" is nothing in a 53' trailer)

Tape-hinge foam yurt (original)

  • 60 lb vibrating AC hangs in a foam hole held by tape — weakest point of the whole build
  • Tape adhesive degrades fast in heat + UV + dust
  • Door = taped foam flap, re-sealed constantly
  • Bare XPS: flammable + UV-degrades
  • One-burn structure
  • Only advantage was folding flat — solved by the semi
Context: we also evaluated a 12V compressor fridge grid (3× ICECO + solar generator): ~$5,400 for only ~10 cu ft. This box gives ~128 cu ft for ~$920 all-in, ~$620 of which is already bought. Walk-in wins on volume-per-dollar by ~70×.

3 · Materials & Cost

Already owned ✅

ItemQtyStatus
Dow Scoreboard XPS 3"×4'×8' (IBDBGR348-SB)4 (confirm)✅ Picked up 7/11
COWSAR 5,000 BTU 115V window AC (manual controls)2✅ Received
PT-15 shrink-wrap tape 6" + BOMEI bifilament tape2+2 rolls✅ Received — now used for seam sealing, not structure
ROMECH hot knife (foam cutting)1✅ Received

To buy (one Home Depot run, ~$320)

ItemQtyEst.Notes
½" CDX plywood 4×85~$200Walls ×3, roof ×1, door + AC frames ×1
¾" CDX plywood 4×8 (floor)1~$55Or double up ½" if cheaper
2×4×8' (skids + floor frame)4~$16
2×2×8' (wall studs, AC + door framing)8~$28
Loctite PL 300 Foamboard adhesive4 tubes~$24MUST be foam-rated — regular PL melts XPS
Deck screws 2½" + 1¼" + fender washersboxes~$30
Gate hinges ×2, gate latch, pull handle1 set~$25Door hardware
Foam weatherstrip + white exterior paint (1 gal)1+1~$40Door seal + solar reflection
Min/max thermometer1~$12Food-safety temp logging

Total new spend: ~$320–350 · Total project: ~$920 (vs ~$5,400 for the fridge-grid alternative)

Panel check: if we have 4× 3" XPS sheets: floor 1 + long walls 2 + ends/door 1 = exactly 4, with the roof uninsulated ply. Grab 1 more XPS sheet (~$60) on the same run for a properly insulated roof — the roof is the biggest heat gain surface.

4 · Cut List & Assembly Order

Cut list (interior 8'×4'×4')

PartPlyXPS
Floor1× ¾" full sheet on 2×4 frame1× full sheet (under-deck, between skids)
Long walls ×22× ½" full sheets2× full sheets (cut height to 4')
End wall (solid)½ sheet ½"½ sheet
End wall (door end) + door½ sheet ½" + door blank ~30"×45"matching pieces
Roof1× ½" full sheet, ½" slope shims1× extra sheet (recommended buy)
AC openings ×2Cut per COWSAR chassis dims + 2×2 frame around each; one low, one high, shaded side

Assembly order (1 build day, 2–3 turtles)

  1. Build 2×4 skid base + floor frame → screw down ¾" deck → XPS between skids.
  2. Frame corners + AC + door openings with 2×2s on the deck.
  3. Skin walls with ply (screws into frame). Cut AC openings with jigsaw before standing walls.
  4. Hot-knife XPS to fit each bay → PL 300 + press → screws w/ fender washers, 16" grid.
  5. Roof: XPS then ply lid with slope shims, screwed to wall tops.
  6. Hang door (XPS+ply sandwich), weatherstrip, latch, handle.
  7. Mount ACs in framed openings — foam gasket + PT-15 flashing tape around chassis (the tapes finally shine here). Condensate drains slope OUTWARD.
  8. Paint white / wrap roof in spare Aluminet. Thermometer inside. Run test: pull-down to 50°F, check seams by feel.
⚠️ Safety notes: XPS is combustible — it stays fully enclosed in ply, the box lives away from the cook line, wiring passes through grommeted holes only. ACs on a GFCI-protected circuit. This is our documented plan — David reviews before build (7/16).

5 · Power & Open Questions

  • Power draw unchanged: same 2 ACs as the original plan — ~4A each, already in the camp power budget.
  • Runtime: R-15 walls + white skin + shade + raised base should mean low duty cycle at 50°F setpoint. The insulated roof upgrade matters most here.

For David / the team (7/16 call)

  1. Blessing on the wood+XPS approach (transport constraint gone — semi arrived ✅)
  2. Panel swap FYI: Dow Scoreboard XPS instead of R-Max PolyIso (less MOOP when cutting, hot-knife compatible; UV/fire managed by ply skin)
  3. Anchoring: rigid ~300 lb box — stakes + ratchet straps over the roof, or is skid weight enough?
  4. Buy 1 extra XPS sheet for the roof — any objection?
  5. Condensate: drip pans / drain lines to greywater, or evaporate-in-place acceptable?