Imported from terminalskills/skills (skills/spec-to-3d/SKILL.md). Install upstream with npx skills add terminalskills/skills --skill spec-to-3d. Copyright stays with the author (Apache-2.0).

Spec to 3D -- Building Model Generator

Overview

Convert structured architectural data (from architectural-drawing-parser or manual specs) into 3D building models. Supports three output formats: Three.js (interactive web viewer), Pascal Editor JSON (BIM-style node graph), and plain JSON (for IFC/GLB conversion). Works as the final stage in a drawing-to-3D pipeline alongside architectural-drawing-parser and ibc-building-codes.

Instructions

Pipeline

Architectural Drawing (image/PDF)
        |  architectural-drawing-parser
Structured BuildingData JSON
        |  ibc-building-codes (validation)
Validated Building Data
        |  spec-to-3d (THIS SKILL)
3D Model Output:
  - Three.js Group (web viewer)
  - Pascal Editor JSON (BIM node graph)
  - Building3D JSON (for IFC/GLB export)

Input Requirements

The generator expects a BuildingData object with:

• stories -- { permitted, actual } (number of floors)
• units -- Array of { name, area: { sqft, sqm }, occupantLoad } (unit types per floor)
• height -- { permitted, actual } in feet and meters
• occupancy and constructionType -- for IBC validation context

Generation Logic

1. Floor-to-floor height: Default 9'-0" (2.74m) per IBC R-2 residential standard (7'-0" minimum habitable)
2. Unit dimensions: Derived from area using 1:1.5 aspect ratio (width:depth). Override for corridor-loaded or deep units
3. Wall thickness: 300mm exterior, 150mm interior partitions (US wood frame standard)
4. Layout: Units placed side-by-side per floor with 150mm party walls, common corridor along one side (5'-0" / 1.52m wide)
5. Stairs: Two stairwells at building ends, 4'-0" wide x 10'-0" deep
6. Room subdivision: Automatic based on unit area -- studio (<50 sqm), 1-bed (50-70 sqm), 2-bed (>70 sqm)

Output Formats

Key Interfaces

interface Building3D {
  levels: Level3D[];
  totalHeight: number;       // meters
  footprintWidth: number;
  footprintDepth: number;
}

interface Level3D {
  elevation: number;         // meters above grade
  height: number;            // floor-to-floor in meters
  units: Unit3D[];
  corridors: Box3D[];
  stairs: Stair3D[];
}

interface Unit3D {
  type: string;
  position: { x: number; y: number; z: number };
  width: number; depth: number; height: number;  // meters
  rooms: Room3D[];
  walls: Wall3D[];
  openings: Opening3D[];
}

Examples

Example 1: Converting a Building Spec to a 3D Model

A developer has parsed data from an IBC compliance sheet for a 3-story R-2 apartment building and wants to generate a 3D model for visualization.

Input BuildingData:
  occupancy: R-2, constructionType: V-B, sprinklerSystem: NFPA 13
  stories: { permitted: 4, actual: 3 }
  units:
    - Type A: 834 SF (77.5 sqm), 5 occupants
    - Type B: 645 SF (59.9 sqm), 4 occupants

Generated Building3D (format: "json"):
  Level 0 (Ground Floor): elevation 0.00m, height 2.74m
    Type A: 7.19m wide x 10.78m deep (2-bedroom layout: living, kitchen, master bed, bed 2, 2 baths)
    Type B: 6.32m wide x 9.48m deep (1-bedroom layout: living, kitchen, bedroom, bath)
    Corridor: full building width x 1.52m deep
    2 stairwells at building ends

  Level 1: elevation 2.74m, height 2.74m (same layout)
  Level 2: elevation 5.49m, height 2.74m (same layout, no stairs above)

  Total height: 8.23m
  Footprint: ~13.66m x 10.78m
  Wall count: 12 exterior + 8 interior per floor
  Openings: 1 door + 2 windows per unit

Example 2: Generating IFC-Compatible Output

An architect needs to export the building data for use in an IFC/BIM workflow. They generate Pascal Editor JSON that maps to a site > building > level > element hierarchy.

Input: Same 3-story R-2 building as Example 1
Output format: "pascal"

Generated Pascal Editor JSON:
{
  "nodes": {
    "site_1700000000": { "type": "site", "parentId": null },
    "building_1700000000": { "type": "building", "parentId": "site_...", "width": 13.66, "depth": 10.78, "height": 8.23 },
    "level_0": { "type": "level", "name": "Ground Floor", "elevation": 0.00, "height": 2.74 },
    "level_1": { "type": "level", "name": "Level 1", "elevation": 2.74, "height": 2.74 },
    "level_2": { "type": "level", "name": "Level 2", "elevation": 5.49, "height": 2.74 },
    "wall_0_0": { "type": "wall", "parentId": "level_0", "start": { "x": 0, "y": 0 }, "end": { "x": 7.19, "y": 0 }, "thickness": 0.30, "isExterior": true },
    "room_0_0": { "type": "room", "parentId": "level_0", "name": "Living Room", "roomType": "living", "width": 4.31, "depth": 4.31 },
    ... (60+ nodes total across 3 levels)
  },
  "rootNodeIds": ["site_1700000000"]
}

This JSON imports directly into Pascal Editor or can be converted to IFC using ifcopenshell.

Guidelines

• Floor-to-floor height defaults to 9'-0" (2.74m); override if the source drawing specifies otherwise
• Unit aspect ratio defaults to 1:1.5; corridor-loaded or deep units may need 1:2 or higher
• Window and door positions are generated algorithmically; use architectural-drawing-parser room extraction for actual positions from drawings
• The Three.js output creates simple box geometry -- suitable for massing models and spatial validation, not photorealistic rendering
• For production BIM use, export to Pascal Editor JSON and refine in a BIM tool
• Stair geometry is simplified (box representation); detailed stair modeling requires a dedicated BIM tool
• All dimensions are in meters internally; input data in feet is converted using 1 ft = 0.3048 m