diff --git a/README.md b/README.md
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@@ -55,6 +55,7 @@ A cyberdeck built from salvaged ASUS K501U laptop components and Orange Pi 3B SB
 - [Design Decisions](docs/design-decisions.md) - Build approach, nomenclature, layout
 - [Power System](docs/power-system.md) - IP5389 battery management decision
 - [Port Layout](docs/port-layout.md) - External port placement and allocation
+- [Case Design](docs/case-design.md) - Dimensional constraints, component footprint, floorplan
 - [Initial Bring-up](docs/initial-bringup.md) - First boot and hardware validation
 
 ## Quick Reference
diff --git a/docs/case-design.md b/docs/case-design.md
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+# Case Design
+
+## Form Factor
+
+Briefcase clamshell:
+
+- **Canopy** — Salvaged K501U laptop lid (display, hinge, bezel). Opens upward, hinge at the bow edge.
+- **Base** — Wooden enclosure holding keyboard, SBC, power, and peripherals.
+
+User sits at the stern, facing the bow. See [design-decisions.md](design-decisions.md) for full nomenclature (deck/keel/bow/stern/port/starboard).
+
+## Dimensional Constraints
+
+### Canopy (Lid)
+
+| Dimension | Value | Source |
+|-----------|-------|--------|
+| Width | 39 cm | Measured, rounded up |
+| Height | 26 cm | Measured, rounded up |
+
+The lid dimension is the *outer* shell of the K501U display assembly (plastic casing + LCD panel + bezel). The glass panel itself is smaller — these are the hinge-to-edge and side-to-side mounting boundaries.
+
+### Base External
+
+Tentative, with ~5mm per-side margin beyond the lid:
+
+| Dimension | Value | Notes |
+|-----------|-------|-------|
+| Width | 40 cm | Lid width + margins |
+| Depth | 27 cm | Lid depth + margins |
+| Height | TBD | Depends on component stacking |
+
+Base height (internal depth of the wooden box) is the critical unknown. It depends on whether all internal components fit in a single Z-slice or require multiple layers.
+
+## Component Footprint Inventory
+
+Measured and estimated dimensions for everything that goes inside the base. These are 2D floorplan sizes (width × depth); height determines minimum internal clearance.
+
+| Component | W × D × H | Notes |
+|-----------|----------|-------|
+| TrackPoint keyboard | ~32 × 11 cm × ~1 cm | Depends on specific model, typical compact USB TrackPoint KB |
+| Orange Pi 3B | 8.5 × 5.6 cm × ~1.5 cm | With heatsink. Mount on standoffs |
+| Display controller (eDP→HDMI) | ~7 × 5 cm × ~1.5 cm | Generic board, may vary. Near hinge |
+| IP5389 power board | ~5 × 4 cm × ~0.5 cm | Thin PCB, mount near cell pack |
+| 18650 cells ×6 (3S2P) | 19.5 × 3.6 cm × 1.85 cm | Each cell 18×65mm. 3 cells end-to-end = 195mm, 2 cells side-by-side = 36mm |
+| USB hub PCB (decased, 10-port) | ~12 × 5 cm × ~1.5 cm | Estimate — depends on specific hub |
+| HDMI A/B switch (mechanical) | ~5 × 3 × 2 cm | Passive toggle. Near hinge |
+| PAM8403 audio amp | ~2.4 × 2.1 × 0.5 cm | Tiny, anywhere |
+| Speakers ×2 | ~3.1 × 7 cm × ~1.5 cm | Small drivers |
+| Cooling fan(s) | 4–8 cm square × ~1 cm | Size TBD based on thermal needs |
+| 5A fuse + holder | ~2 × 2 × 1 cm | Inline on power rail |
+
+## Floorplan Strategy
+
+The deck surface has two fixed-location items:
+
+1. **Keyboard** — centered, user-facing (stern edge). ~32 cm wide leaves ~4 cm per side within a 40 cm base width for misc ports or switches.
+2. **Hinge mount** — along the full bow edge, structural.
+
+Everything else floats between them. The major volume items:
+
+- **Battery pack (19.5 × 3.6 cm)** — longest rigid item other than the keyboard. Placement candidates:
+  - Behind the keyboard (between keyboard rear and hinge area) — requires ~20 cm of unobstructed depth behind the keyboard
+  - Along port or starboard side — uses the 4 cm gutter on one side
+  - Under the keyboard — possible if keyboard is a flat membrane type, unlikely for a mechanical
+
+- **OPi 3B + USB hub** — moderate footprint, flexible placement. Could sit in the area behind the keyboard alongside the battery pack.
+
+- **Display controller + HDMI switch** — short HDMI cable runs dictate they live near the hinge.
+
+### Depth Dimensions (Front-to-Back)
+
+```
+Bow edge (back)
+│
+[hinge area — 2-3 cm]
+[display controller / HDMI switch]
+[battery pack and/or SBC/hub zone]
+[keyboard — 11 cm]
+[palm rest area — 5-8 cm]
+│
+Stern edge (front)
+```
+
+Total: roughly 18-22 cm front-to-back for keyboard + palm rest, plus 15-20 cm behind keyboard for electronics. That fits within a ~27 cm base depth with room to spare.
+
+### Port-Starboard Layout (Width)
+
+```
+Port edge (left)                 Starboard edge (right)
+│                                  │
+[2 cm gutter] [keyboard ~32 cm] [2 cm gutter]
+```
+
+The gutters can hold the vertical battery pack, side-mounted ports, or switch cutouts.
+
+## Z-Stack (Depth/Layer Planning)
+
+**Goal: single-slice layout** — all boards and components mounted on the same plane (the keel), with nothing stacked above or below.
+
+Feasibility check:
+- Tallest component: speakers at ~1.5 cm, OPi with heatsink at ~1.5 cm, HDMI switch at ~2 cm
+- Battery pack at 1.85 cm
+- Leave ~5 mm clearance above tallest item → internal clearance of ~2.5 cm
+- Wood base walls at ~1 cm each → total case height ~4.5 cm
+
+This keeps the case within briefcase norms (~8-13 cm is the typical range, but thinner is fine) and avoids the weight and complexity of a second deck layer.
+
+## Open Questions
+
+- [ ] Exact TrackPoint keyboard model — dimensions and mounting method
+- [ ] Battery pack placement — behind keyboard vs side gutter
+- [ ] Fan size and placement — SBC heatsink fan vs case fan
+- [ ] Lid latch mechanism — holds canopy closed in transit
+- [ ] Hinge reattachment — how to mount K501U hinge to wooden base
+- [ ] Cable routing paths — power, HDMI, USB within the case
+- [ ] SD card reader location — stern edge per port layout
+- [ ] Kensington lock slot — stern edge
+- [ ] Wood thickness and joinery method
+
+## Revision History
+
+| Date | Change |
+|------|--------|
+| 2026-06-03 | Initial — dimensional constraints and floorplan approach |
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