The BIM Layer

brepjs-bim turns brepjs geometry into building information. You describe elements as typed parametric specs (a wall is a length, height, thickness, placement, and material, not a mesh); the model assembles them into a spatial structure (project → site → building → storey), layers on property sets, materials, quantities, and classifications, and serializes the result to a valid IFC-SPF file. A matching importer reads IFC back in.

npm install brepjs-bim brepjs web-ifc

Two ways in:

• Through families (recommended for new models): author a declarative element tree with brepjs-families and project it with familiesToBim. Identity, openings, and containment come from the tree; GlobalIds derive from key paths and survive reorders. Start at IFC Export.
• Direct BimModel: imperative add* calls when you already know exactly what to build, or when you need elements the families projection does not cover yet.

import { BimModel, toIfc } from 'brepjs-bim';
import { unwrap } from 'brepjs';

const model = new BimModel();
model.init({ name: 'Example' });

const siteId = unwrap(model.addSite({ name: 'Site' }));
const buildingId = unwrap(model.addBuilding({ name: 'Building' }));
const storeyId = unwrap(model.addStorey({ name: 'Level 1', elevation: 0 }));
const project = model.getProject();
if (project) model.aggregate(project.localId, siteId);
model.aggregate(siteId, buildingId);
model.aggregate(buildingId, storeyId);

const wall = model.addWall({
  length: 4000,
  height: 3000,
  thickness: 200,
  origin: [0, 0, 0],
  axisX: [1, 0, 0],
  axisZ: [0, 0, 1],
  materialName: 'Concrete',
});
if (wall.ok) model.placeIn(wall.value, storeyId);

const ifc = await toIfc(model, { applicationName: 'example-app', applicationVersion: '1' });
// ifc.ok && ifc.value instanceof Uint8Array

Three design decisions carry the package:

1. Specs are the source of truth. Every add* call validates its spec (zod schemas; the parse*Spec functions are exported for standalone use), builds the brepjs solid analytically, and stores a typed element. The IFC writer emits parametric entities (IfcExtrudedAreaSolid, profile defs) from the same spec, so the exported file stays editable data, not frozen triangles.
2. Geometry is unplaced template geometry. Element solids live in local coordinates; origin / axisX / axisZ are applied by the IFC layer via IfcLocalPlacement. Use placedSolids(element) when you need world-placed solids for display.
3. Results, not exceptions. Every operation returns Result<T, BimError> from brepjs. Validation issues travel inside reports; nothing throws across the API boundary.

Dimensions are millimeters everywhere; IFC export emits SI metres. Reading element geometry needs only the brepjs kernel; toIfc / fromIfc additionally load the web-ifc peer dependency.

Continue with the element catalog, IFC export & import, validation, and interop.