# LDD-03 · Gym/Living Spine Wall

> **Status:** 🟢 LOCKED v2.0 — replaces all prior spine wall concepts.

## One-line intent

A structural glass spine that unifies gym and living visually, while maintaining structural, acoustic, and environmental separation through modular glazing flanking a central 18'×10' glass sectional garage door.

## Why this matters

The spine wall is the project's central architectural organizing element and the most identity-defining single feature. It's also one of the highest-coordination items — structure, acoustic, thermal, environmental, and visual all converge here.

## Locked decisions

**Location + extent**

- Along gym/living wing boundary, ~60' long N–S (central 60' core)
- West = gym volume, East = downstairs living wing
- Upstairs UCR / pajama lounge remains visually open to gym above the spine wall zone

**Structural integration**

- Spine beam integrated into primary PEMB structure
- Two offset structural columns only; **no center column**
- **Three structural spans along the 60' wall**: north end ~17' · central ~26' · south end ~17'
- ~30' clear central viewing zone preserved between offset columns
- Per builder, this enables **standard steel gauges** rather than the prohibitive cost of a 60' unsupported beam, while still hitting the 30' viewing aperture target
- Spine beam supports the **18" second-floor assembly** above (deck + joists + gypcrete radiant topping + finish)

**Glazing system**

- Modular mullion glazing — ~36" × 24" panel rhythm throughout
- One central glass sectional garage door, ~18' wide × 10' tall
- Manual counterbalanced operation preferred
- Flanking glazing fields with consistent rhythm on both sides

**Glass intent**

- Laminated safety glazing under active consideration
- Low-E coating under active consideration
- Final acoustic/thermal spec to be coordinated with HVAC and comfort strategy

**South → North wall sequence (locked)**

| Span | Element |
|---|---|
| 8' | Solid wall |
| 3' | Door |
| 3' | Glass panel |
| — | Structural column |
| 3' | Glass panel |
| 3' | Glass panel |
| 18' | Glass garage door |
| 3' | Glass panel |
| 3' | Glass panel |
| — | Structural column |
| 3' | Glass panel |
| 3' | Door |
| 8' | Solid wall |

**Solid wall assembly**

- Independent framed wall assemblies
- Mineral wool acoustic insulation
- Sealed penetrations
- Drywall and/or selective interior finish layers
- Service routing capability integrated within wall depth

**Acoustic strategy**

- Insulated stud wall assemblies + mineral wool
- Sealed penetrations, controlled glazing interfaces
- Independent HVAC zoning between gym and downstairs living wing

## Open items / requires engineer review

- Final glass spec (laminated thickness, lite count, gas fill, Low-E surface)
- STC target for solid wall vs glass — gym basketball play hits ~95 dBA at impact; spine wall STC should be specified (target STC 45–50 reasonable, would need designed assembly)
- Garage door specification: manufacturer, glass weight, counterbalance hardware, header detail
- Door type at the two 3' door positions (swinging vs sliding)
- Threshold detail (slab continues through, or break)
- Thermal continuity across the spine wall in winter — partial boundary means partial thermal performance; how much heat is gym willing to share with living?

## Cross-references

- ← [LDD-01 structural](01-structural-pemb.md) — spine beam + offset column geometry.
- ← [LDD-05 HVAC](05-hvac-system.md) — separate gym vs living zoning depends on this wall as boundary.
- ← [LDD-08 lighting](08-lighting-framework.md) — mullion rhythm coordinates with linear LED runs.
- → [LDD-04 west gym hero wall](04-west-gym-hero-wall.md) — paired with this wall as the gym's two long-edge experiences.

## Cost drivers

- **Glass garage door (18' × 10')** with all-glass panel option: $12–24K depending on specification, plus hardware $4–7K. Manual counterbalance saves $2–4K vs powered.
- **Modular mullion glazing** (~370 sqft of glass total in the spine wall flanking fields): $80–140/sqft installed for thermally broken aluminum with laminated low-E ≈ $30–52K.
- **Two interior structural columns** included in LDD-01 budget.
- **Solid wall sections** (~16' × 12' = ~190 sqft × 2 = ~380 sqft wall area) at $25–40/sqft built-out with mineral wool, drywall, and finish ≈ $10–15K.

**Likely-case rollup for spine wall (glazing + door + finish, excl. structure): $60–95K.**

## Air-gap concerns

1. **STC across an 18' garage door is the limiting acoustic factor.** Even premium glass garage doors will let basketball impact and gym chatter through to the living wing. If acoustic separation is important for, say, watching TV while someone shoots hoops, plan to close the garage door + use the two solid 8' wall ends as the real acoustic mass — and accept that the glass panels are an acoustic compromise the design has deliberately chosen.
2. **Manual counterbalanced 18' door is heavy.** Even a perfectly balanced 18' × 10' all-glass sectional weighs 600–900 lb. "Manual" still means a heavy door with springs that need maintenance and that a kid shouldn't operate alone. Consider safety reversing + soft-close hardware.
3. **Mullion rhythm vs cleaning access.** A 36" × 24" rhythm on a 60' wall = 30+ glass panels, each with seals, gaskets, and hardware. The cleaning regimen and replacement-glass procurement schedule should be planned.
4. **Door threshold continuity through the spine.** If you can drive a wheelchair, scooter, or BBQ cart from kitchen into gym, the threshold under the 18' door has to be flush. This affects slab pours on both sides and the radiant tubing layout.

## Diagram

![Spine wall south-to-north elevation sequence](../../diagrams/03-spine-wall-elevation.svg)

## Status

🟢 **Green — geometry locked, sequence is buildable.** Specification of glass + door hardware is the remaining detail work.