# LDD-10 · Plumbing — Three Clusters

> **Status:** 🟢 LOCKED v2.0 — supersedes all previous plumbing LDDs.

## One-line intent

Three zones, tight stacks, short runs — everything falls cleanly to the east.

## Why this matters

This is the most disciplined LDD in the set. The three-cluster, vertically-stacked, east-side-drain strategy is exactly how plumbing should be organized in a building with this footprint and program variety. The non-negotiable rules section reads like an engineer's checklist.

## Locked decisions

**Three independent east–west clusters**, each vertically stacked and internally contained.

**Non-negotiable rules**

- No cross-cluster fixture mixing
- No long horizontal routing between clusters
- Vertical stacking prioritized within each cluster
- System must remain legible, organized, repeatable

### North cluster

**Location:** north end of living wing + ILS

**Serves:**

- Ground: large bathroom (Murphy bed zone), ILS bathrooms (shared wet wall)
- Upper: two north bedroom bathrooms

**Special case: ILS kitchen sink** (~20' from north cluster wall)

- Option A (preferred): routed within floor system back to north cluster stack with proper slope
- Option B (allowed): local vertical drop near sink, ties to main building drain under slab

### Middle cluster

**Location:** central living wing

**Serves:**

- Ground: kitchen sink + dishwasher, WC, mech room (support only)
- Upper: laundry / ops core, two bathrooms

**Character:** highest-density plumbing zone; primary service spine; tight integration with mechanical room.

### South cluster

**Location:** south bay

**Serves:**

- Ground: workshop WC, workshop utility sink, equipment room utility sink, equipment room floor drain
- Upper (LOW): bathroom/shower, optional kitchenette sink

**Classification:**

- Primary stacked: workshop WC, LOW bathroom (toilets stack)
- Secondary offset: equipment sink + floor drain, workshop sink (short horizontal runs allowed)

### Vertical stack rules

- Each cluster has its own vertical stack(s)
- No shared stacks between clusters
- Toilets ≤ 6–8 ft from stack
- Vertical alignment prioritized
- Offsets allowed only for non-critical fixtures

### Horizontal distribution

- Confined to wet walls and floor systems only
- Prohibited: cross-cluster routing, long horizontal runs, plumbing in exposed ceilings, soffits for plumbing

### Main building drain

- Under slab, runs east side N → S
- Each cluster connects at nearest practical point
- Discharges to site sewer

### Site sewer

- Primary connection on east side of structure, aligning with public sewer running N–S along east side of lot

## Open items / requires engineer review

- **Hot water strategy** — central tank? Distributed tankless? Hybrid heat-pump water heater? Not specified. Major cost + comfort + energy decision.
- **Recirculation lines** for hot water at distant fixtures (ILS kitchen sink especially) — without recirc or a localized point-of-use heater, ILS kitchen will wait 60+ seconds for hot water.
- **Fixture quantities and specifications** — counted from LDDs but never tabulated.
- **Drain venting strategy** — code-required AAVs vs through-roof vents; in exposed-ceiling building, through-roof venting needs careful coordination.
- **Water softener / filtration** — not mentioned. Mountain-West rural water often has hardness, sometimes arsenic, often sediment. Spec accordingly.
- **Backflow prevention** — required by most codes; coordinate with site sewer connection.
- **Gas service** — if generator (LDD-09) or future cooktop changeover is propane/NG, plumb stubouts.

## Cross-references

- → [LDD-15 mechanical room](15-mechanical-room.md) — middle cluster sources from here.
- ← [LDD-13 south bay](13-south-bay.md) — south cluster serves workshop / equipment / LOW.
- ← [LDD-21 laundry / ops](21-laundry-ops.md) — upstairs middle cluster includes laundry.
- → [LDD-02 radiant slab](02-radiant-slab.md) — under-slab drain and radiant tubing must not conflict.

## Cost drivers

- **Drain-waste-vent (DWV) rough-in**: ~$8–14 per linear foot installed. Three clusters with vertical stacks + east main = ~250–350 lf = **$2–5K** for DWV pipe and labor.
- **Supply piping (PEX/copper)**: ~$3–6/sqft of building footprint = **$22–43K** for a 7,200 sqft building.
- **Fixtures**: kitchen + 2 main + 2 ILS + 1 WC + workshop WC + LOW bath = ~7 toilets, ~10 sinks, 3+ showers/tubs. At mid-spec: $25–45K.
- **Hot water system**: heat-pump water heater $4–7K, or distributed tankless $6–12K, or central tankless $4–8K + recirc $1–3K.
- **Water softener / filtration**: $2–6K.
- **Backflow / site connection**: $2–5K (excluded from this rollup if part of site prep).

**Likely-case rollup: $90–135K total plumbing.** Budgeted at $115K in the waterfall.

## Air-gap concerns

1. **The ILS kitchen sink offset is the only weak point** in an otherwise extremely clean strategy. If Option B (local drop) is used, document the location and ensure the under-slab routing doesn't intersect a column footing.
2. **Hot-water wait time at ILS kitchen** if there's no recirculation or POU heater. 20' from the cluster + cold pipe = a meaningful daily friction point. Specify the answer now.
3. **No mention of slab penetrations being coordinated with radiant tubing.** LDD-02 says "penetrations coordinated before pour" — verify that plumbing under-slab is fully documented before the radiant guy starts pulling tubing. Plumbing wins; radiant routes around.
4. **East main drain runs the full 120' length under slab.** Single drain line failure = whole-building disruption. For a 50-year build, consider a cleanout strategy at each cluster intersection, not just at the ends.
5. **Vent stacks must penetrate the roof** in an exposed-ceiling, organized-MEP-routing building. Locate stacks now so the roof penetrations align with structural bays, not random over a TV wall.
6. **No water-softener bypass for outdoor hose bibs.** If hard water is treated for the whole house, outdoor watering wastes salt regen. Add a bypass at the inlet.

## Diagram

![Three plumbing clusters with east main drain to site sewer](../../diagrams/06-plumbing-clusters.svg)

## Status

🟢 **Green — the discipline here should be the model for the rest of the LDD set.** Resolve hot-water strategy + recirculation before bidding.