# LDD-24 · Flooring Systems + Threshold Integration

> **Status:** 🟡 PENDING LOCK — strategy specified by builder (Peter, 2026-05-15); awaiting integration with radiant + spine wall threshold detail.
>
> **Source:** Inbound builder spec — "LDD-FINISH-01" — added to LDD set 2026-05-15.

## One-line intent

Flooring directly supports the operational and sensory needs of each zone, with a strictly flush, zero-threshold datum across the 60' spine wall opening.

## Why this matters

This LDD answers a question the original set left silent: what's on top of the slab in each zone? More importantly, it forces the slab itself to be poured to **multiple finish elevations** so that the finished floor reads as continuous from gym to living wing — a meaningful structural / formwork demand that has to be resolved before slab pour, not after.

## Locked decisions

### System allocation by zone

| Zone | System | Reason |
|---|---|---|
| Gym (west of spine wall) | High-performance poured polyurethane top coat over dual-layer or single-layer vulcanized rubber underlayment | Shock absorption · acoustic dampening · longevity under athletic loads |
| Living wing / ILS (east of spine wall) | High-density rigid-core SPC (Stone Plastic Composite) LVP with factory-attached cushion (IXPE foam or engineered cork) | Thermal stability over radiant slab · standing comfort · room acoustics · no hollow sound |
| Workshop / parking / mech (south + central service) | Industrial sealed and polished concrete | Per foundation LDD; durable, cleanable, compatible with vehicle loads |

### Radiant compatibility constraints

- **SPC core only.** WPC and loose-lay LVP are **strictly prohibited** (buckling and off-gassing risks).
- **Maximum continuous slab surface temperature beneath the LVP** shall be calibrated to the manufacturer's warranty threshold — typically **85°F**.
- Adhesives (if required at high-traffic zones) must be rated for continuous radiant exposure without VOC release over 20+ year lifecycle.

### Spine wall threshold mandate (the load-bearing requirement)

The gym urethane floor assembly (~8–10 mm) is thicker than the residential SPC LVP (~6–8 mm). Therefore:

- **Zero Improvisation Rule:** the underlying structural concrete slab must be micro-adjusted or self-leveled across the threshold of the 18'×10' glass garage door along the 60' spine wall so finish elevations match.
- **Outcome:** the final finished floor across the spine wall opening must be **100% flush**. No T-moldings, step-ups, bevels, or trip-hazards permitted.

> ⚠️ **Pier foundation cascade** — see [LDD-01 site context](01-structural-pemb.md#site-context-delaware) and [LDD-02 foundation cascade note](02-radiant-slab.md). If the first floor is a wood subfloor on piers (option b) rather than a structural slab (option a), the entire flooring assembly stack changes. Lock foundation type before specifying urethane gym floor + LVP transitions.

## Open items / requires engineer review

- **Exact assembly stack-up** for each zone — Peter's spec gives ranges (8–10 mm gym, 6–8 mm LVP). Lock the actual product before slab pour so the delta is known.
- **Slab elevation drop on the gym side**: needs to be ~2–4 mm lower than the LVP side so finished floor matches. Confirm formwork tolerance is achievable (typical concrete tolerance is ±¼" = 6 mm — tighter than that requires self-leveling overlay, which is an added line item).
- **Spine wall threshold transition strip**: even with "100% flush," there is still a butt joint where urethane meets SPC LVP. Decide if this is a hard butt, a small flexible filler, or a metal flush-edge transition. Each has implications for cleanability and aesthetics.
- **Radiant slab control setpoint** in living wing — 85°F slab temp ceiling is binding; verify mechanical designer (LDD-02) is calibrated to this constraint. A comfort-density radiant slab in cold-climate winter can easily hit 90–95°F surface — that exceeds the warranty.
- **Urethane gym floor brand + warranty** — affects color, slip rating, line marking compatibility (basketball lines!), repair regimen.
- **SPC LVP brand + warranty** — radiant compatibility statement from manufacturer in writing.
- **Polished concrete finish level** for the workshop / garage / mech zones — Class 1 (matte) vs Class 3 (semi-polished) vs Class 4 (highly polished). Different cost, different look, different traction.
- **Basketball line painting / sport markings** on the urethane floor — included? Cost adder.

## Cross-references

- → [LDD-02 radiant slab](02-radiant-slab.md) — **the 85°F cap is a real constraint on radiant setpoint and outdoor reset curves.**
- → [LDD-03 spine wall](03-spine-wall.md) — **the 100% flush threshold mandate is a coordination point for slab formwork.**
- → [LDD-18 interior materials](18-interior-materials.md) — flooring is part of the interior material language hierarchy.
- → [LDD-22 basketball hoop](22-basketball-hoop.md) — slab anchorage for hoop frame must penetrate urethane assembly cleanly.
- ← [LDD-01 structural](01-structural-pemb.md) — slab thickness + reinforcement now have a slightly more complex elevation pattern than uniform.

## Cost drivers

- **Gym urethane floor system** (poured PU over vulcanized rubber): $9–16/sqft installed. Gym area ≈ 1,800 sqft (central west bay, gym side of spine). **$16–30K.**
- **SPC LVP with cushion backing**: $5–10/sqft installed. Living wing + ILS + upper living ≈ 4,200 sqft. **$21–42K.**
- **Polished concrete (Class 2–3)**: $4–9/sqft. Workshop + garage + mech ≈ 2,400 sqft. **$10–22K.**
- **Self-leveling overlay** at spine wall threshold zone for elevation match: $2–6/sqft × ~50 sqft = **$0.5–1K** (small).
- **Basketball court line painting**: $1.5–4K.
- **Transition strip / flush metal edge at spine threshold**: $0.5–2K.

**Likely-case rollup: $50–95K total flooring + transition.** *(This was not explicitly in the original waterfall — the budget rollup needs to add ~$70K. The waterfall has been updated.)*

## Air-gap concerns

1. **The 85°F slab cap is the most important interlock.** Comfort-density radiant in a cold-climate January with a 65°F room setpoint can easily push slab surface to 90°F to keep up. The mechanical designer must calibrate the curve so the LVP zone never exceeds 85°F continuous. If it can't, either pick a thinner SPC with higher temperature rating or accept that the LVP warranty is voided — neither is great. **Verify in writing with the LVP manufacturer that 85°F continuous is the cap, and design radiant to never exceed it.**
2. **"Self-leveling across the spine wall threshold" is a real construction sequencing challenge.** Concrete tolerance is normally ±¼" — finer than that needs a high-flow self-leveling underlayment poured after the structural slab cures. Build this into the schedule, not as a "we'll do it during finish" item.
3. **Vulcanized rubber underlayment + urethane top = considerable acoustic + impact damping**, which is excellent for basketball but reduces the floor's stiffness underfoot. Pro-grade gymnasiums use this assembly; weekend league play may feel "spongier" than expected. Set expectations.
4. **Polished concrete in mech room** can be slippery when wet. Plan for hot water heater leaks, radiant manifold drips — the mech room WILL have water on the floor at some point in 50 years. Spec a slip-rated finish (DCOF ≥ 0.42 wet).
5. **Workshop concrete + oil + tool drops** = chipping. Polished concrete shows chips. If heavy fabrication is anticipated, consider a urethane cement overlay in the workshop main work zone (additional ~$8–12/sqft for ~300 sqft = $2.5–4K).
6. **Off-gassing during the first 30 days.** SPC LVP + urethane gym + polished concrete sealer all off-gas. Plan a 14-day flush-out window with high ventilation before move-in, especially for the ILS occupant.
7. **No mention of mats/rugs**, which on radiant slab can create hot spots and shorten radiant life. Document a "no thick rugs on heated zones" rule in the homeowner manual.

## Diagram

(no dedicated SVG yet — see [program zoning](../../diagrams/02-program-zoning.svg) for system allocation map; threshold detail at spine wall is too small for current SVG set, consider Codex prompt for cutaway detail.)

## Status

🟡 **Yellow — direction is correct, several open items must lock before slab pour.** The 85°F radiant cap + the flush spine threshold are the two coordination points that have to land in the next two weeks of design work to avoid rework.