A derivation that walks the modelled building and emits a categorised bill of materials — Framing, Sheathing, Trim, Doors & Windows, Fasteners, Foundation. Lumber comes from each member's cut length and nominal size; roof and wall steel are counted per drawn face; trim runs are measured off the trim panels the engine actually placed; concrete comes from post-hole volume.
Also called: material list · bill of materials · BOM · post frame material takeoff · how much lumber do I need
- 1deriveTakeoff(DerivedBuilding) reads d.members and d.panels — the same objects the renderer uses
- 2Framing cuts are first-fit packed into yard stock lengths
- 3Roof faces are panelised at the roofing profile's coverage width, with waste by face shape
- 4Wall steel is grouped per rectangle at its own height; gable triangles get their own line
- 5Trim is summed per run type from the trim panels drawn (rake, eave, ridge, corner, headwall…)
- 6Fasteners use the SmartBuild sheathing-package formula {sf} × 1.8
- 7Foundation is π r² × embedment × hole count, converted to cubic yards
The header states the discipline: 'Quantities are measured off the SAME members and skins the renderer draws, so the picture and the order cannot silently diverge… every BOM line back-references geometry.' The file also records where each formula came from — screws from the SmartBuild sheathing package, panel coverage from the roof profile, lumber from a first-fit into 8/10/12/14/16/20 ft stock, concrete from hole volume at 18in diameter.
- A hand-counted list drifts from the design as soon as the design changes
- A quantity nobody can trace back to the building cannot be checked
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