# LDD-12 · Exposed Ceiling Systems

> **Status:** 🟢 LOCKED.

## One-line intent

The ceiling is a designed system, not exposed chaos.

## Why this matters

This LDD is the doc set's strongest discipline. Most "exposed ceiling" buildings devolve into a tangle of ducts, conduit, sprinkler lines, and miscellaneous infrastructure that the designer hoped would read as "industrial." Here, the hierarchy is explicit and the routing rules are absolute. If held, this becomes one of the defining experiences of the building.

## Locked decisions

**Core rule**

Everything must be **straight, aligned, intentional**.

**Hierarchy (highest priority placed first; lower layers must defer)**

1. Structure (PEMB frames, purlins, spine beam)
2. Main HVAC trunk
3. Branch ducts
4. Electrical conduit
5. Lighting

**Routing rules**

- Only N–S or E–W
- Only 90° intersections
- **No diagonal runs**
- **No zig-zags**

**Duct strategy**

- Round ducts only
- Long straight runs
- Aligned to structure

**Electrical**

- Bundled
- Parallel runs
- Clean vertical drops only

**Lighting**

- Linear
- Aligned
- No random placement

## Open items / requires engineer review

- **Sprinkler / fire protection routing**, if required by code, has not been called out in the hierarchy. Where does it sit?
- **Communications cabling** (Cat6, fiber, AV) — same question.
- **Plumbing vent stacks** through the roof — these pierce the ceiling plane vertically and must be located now in coordination with the hierarchy.
- **Smoke detectors, CO detectors, security sensors** — placed where? They're always last and always look terrible. Plan them in.
- **Acoustic treatment** — exposed ceiling = no acoustic absorption. The gym in particular will be reverberant. Identify acoustic panels or baffles as needed (and where they sit in the hierarchy).

## Cross-references

- ← [LDD-01 structural](01-structural-pemb.md) — layer 1.
- ← [LDD-05 HVAC](05-hvac-system.md) — layers 2/3.
- ← [LDD-09 electrical](09-electrical.md) — layer 4.
- ← [LDD-08 lighting](08-lighting-framework.md) — layer 5.
- → [LDD-17 soffit system](17-soffit-system.md) — soffits are the controlled exceptions.

## Cost drivers

The exposed ceiling philosophy is mostly free at material level but is **expensive in labor and coordination**. Costs are embedded in each of the contributing trades:

- Ducts: smooth long runs cost ~5–15% more than typical residential ductwork because each elbow is a long-radius and each takeoff is a wye, not a hard tap.
- Electrical: bundled parallel conduit costs ~10–25% more than typical residential.
- Coordination: build a **BIM model or detailed RCP (reflected ceiling plan)** before any rough-in. Designer / coordinator fee $8–18K.

**Net cost premium baked into the trade lines, not separately budgeted.** Roughly $20–35K of premium across HVAC + electrical + coordination.

## Air-gap concerns

1. **Acoustic dead-end.** Hard-surface PEMB + IMP + concrete slab + exposed ceiling = a reverberant building. The gym especially will echo like a high school. Plan acoustic panels (and put them in the hierarchy — they probably belong at layer 5.5, integrated with lighting or as discrete absorber zones).
2. **Sprinklers may be code-required.** A 7,200 sqft mixed-use building including a workshop is sometimes subject to NFPA 13 / 13R sprinkler requirements. Sprinklers in exposed ceilings need careful routing or they kill the visual goal. Verify with AHJ now, not later.
3. **Coordination cost.** "Aligned, intentional, straight" requires every trade to coordinate against a single ceiling plan. A general contractor who hasn't done this is going to push back and want to improvise in the field. Hire a GC who has and budget the coordinator time.
4. **Cleaning.** Exposed ceilings collect dust on every duct top. Plan a 6–12 month vacuuming regimen and design for tall-ladder access (and don't put fragile lighting in places where the ladder will hit it).
5. **Anchor points for future hooks / pull-up bars / hanging plants etc.** The gym ceiling especially deserves a designed grid of structural anchor points. Easy to detail now, expensive later.

## Diagram

![Exposed ceiling hierarchy layers from structure to lighting](../../diagrams/10-ceiling-hierarchy.svg)

## Status

🟢 **Green — hold the line.** Acoustic strategy and sprinkler determination are the only outstanding items.