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SIP Interface Rules

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Static connection rules between SIP components: roof-to-wall, wall-to-foundation, wall-to-wall corners, and opening-to-wall. Injected alongside domain skills.

/skills/sip_interfaces.md

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# SIP Interface Rules Skill

This skill describes the **static connection rules** between SIP component types. Every agent that interfaces with another component receives this skill. Use it to know which side of a connection you are responsible for, and what dimensions to use.

Dimensional values are declared in the `connection_details` catalog injected into this stage. Reference catalog entries by key rather than hardcoding values.

> **Note on dynamic dimensions:** This skill covers interface *rules* (who cuts what, where). The *actual dimensions* of adjacent components (e.g. the exact thickness of the roof panel chosen for this project) are resolved at manifest time and passed via the agent's `domain_knowledge` and `interfaces_provided` fields. Use those values when available; fall back to catalog defaults when not.

---

## Roof-to-Wall Interface

**Rule:** The wall agent is responsible for the connection geometry at its top edge. The roof agent bears on the wall top plate and does not modify the wall.

**Wall agent responsibilities:**
- The double top plate (2× 45×90mm timber) provides the bearing surface for the roof panel.
- For pitched roofs: the top plate must be cut at the pitch angle so the roof panel bears flat. Model this as an angled-cut top plate or use a separate angled bearer.
- For flat roofs: the top plate is horizontal; the roof panel bears flat on it with no cuts needed.
- The wall top plate depth is `CORE_THICKNESS` (not `TOTAL_THICKNESS`) — it slots into the foam groove.

**Roof agent responsibilities:**
- The roof panel eave end bears on the wall top plate.
- For pitched roofs: cut the eave bevel (`eave_bevel_y = TOTAL_THICKNESS / tan(PITCH_RAD)`) so the panel bears cleanly.
- For flat roofs: the panel bottom face sits directly on the top plate — no cuts needed.

**Shared dimension:**
- `PANEL_THICKNESS` (wall SIP total thickness) defines the inset for roof panel positioning:
  - Mono-pitch: `Placement(Vector(0, PANEL_THICKNESS, EAVE_HEIGHT), rot)`
  - Duo-pitch south: `Placement(Vector(0, PANEL_THICKNESS, EAVE_HEIGHT), rot)`
  - Duo-pitch north: `Placement(Vector(0, BUILDING_DEPTH - PANEL_THICKNESS, EAVE_HEIGHT), rot)`

---

## Wall-to-Foundation Interface

**Rule:** The wall agent is responsible for the sole plate (bottom plate) at Z=0. The foundation agent is responsible for the slab surface and DPC layer.

**Wall agent responsibilities:**
- Create a 45×90mm PT timber bottom plate at Z=0 as the first solid.
- Plate depth = `CORE_THICKNESS` (not `TOTAL_THICKNESS`) — it slots into the foam groove.
- Y-offset = `FACE_THICKNESS` so OSB skins overhang on both faces.
- SIP panels start at Z=90 (top of bottom plate).

**Foundation agent responsibilities:**
- The slab top surface is at Z=0.
- A DPC (damp proof course) layer sits between slab and bottom plate — model as a 3mm high-density polyethylene layer if required, or omit for clarity.
- The slab extends `SLAB_OVERHANG` (minimum 200mm) beyond the wall footprint on all sides.

**Connection detail:** `sole_plate_to_slab` in the `connection_details` catalog.

---

## Wall-to-Wall Corner Interface

**Rule:** For L-corners, one wall runs full length to the outer face; the perpendicular wall butts against it. A double block spline fills the internal corner pocket.

**Responsibility split:**
- The "full-length" wall includes the corner panel at its end — no special treatment needed.
- The "butting" wall's end panel butts against the exterior OSB face of the full-length wall. Its bottom plate runs to the face of the full-length wall. A double block spline (2× 45×90mm) fills the corner pocket on the butting wall's end.

**Corner spline geometry:**
```python
# Double block spline at L-corner (butting wall end)
# Both splines sit in the foam channel, side by side
spline_a = Part.makeBox(45, 90, PANEL_HEIGHT,
                        Vector(x_corner, (TOTAL_THICKNESS - 90) / 2, BOTTOM_PLATE_H))
spline_b = Part.makeBox(45, 90, PANEL_HEIGHT,
                        Vector(x_corner + 45, (TOTAL_THICKNESS - 90) / 2, BOTTOM_PLATE_H))
```

---

## Opening-to-Wall Interface

**Rule:** Openings (windows, doors) are framed within the wall component. The wall agent is responsible for stopping SIP panels at the king stud face and building the full-depth timber buck. If a window or door is described in the wall brief, the wall component includes all framing — there is no separate framing agent.

**King stud depth:** `KING_D = TOTAL_THICKNESS` (full wall thickness, not 90mm).

**Opening agent (if separate):** A separate opening agent adds only the glazed unit or door leaf — it does NOT build framing. Its X position, width, and height come from the wall agent's `interfaces_provided`.

---

## Quick Interface Checklist

Before generating any component that touches another, confirm:

| Check | Wall | Roof | Foundation | Opening |
|---|---|---|---|---|
| Sole plate at Z=0 with CORE_THICKNESS depth | ✅ my responsibility | — | — | — |
| Top plate angled for pitched roof | ✅ my responsibility | — | — | — |
| Eave bevel cut | — | ✅ my responsibility | — | — |
| Slab extends SLAB_OVERHANG beyond walls | — | — | ✅ my responsibility | — |
| King studs are TOTAL_THICKNESS deep | ✅ (if I have openings) | — | — | ✅ |
| Corner spline on butting wall end | ✅ (butting wall only) | — | — | — |
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