diff --git a/.trellis/spec/blender/index.md b/.trellis/spec/blender/index.md
index 1d9cb9b..42b98fc 100644
--- a/.trellis/spec/blender/index.md
+++ b/.trellis/spec/blender/index.md
@@ -37,7 +37,8 @@
 │   osmassets/mesh.py       MeshBatch 等几何构建            │
 │   osmassets/materials.py  材质构建（消费 catalog 的声明）  │
 │   osmassets/tree.py       树实例化                        │
-│   osmassets/water.py grass.py scrub.py   要素装配         │
+│   osmassets/water.py grass.py scrub.py                    │
+│   osmassets/building.py fountain.py   要素装配            │
 │                                                          │
 │   generate_scene.py   export_cesium.py   两个入口         │
 │   tools/scene_digest.py                  结构摘要工具      │
@@ -120,14 +121,15 @@
 
 | 文件 | 行数 | 层 |
 |---|---|---|
-| `generate_scene.py` | 999 | bpy · 入口 |
-| `export_cesium.py` | 624 | bpy · 入口 |
+| `generate_scene.py` | 899 | bpy · 入口 |
+| `export_cesium.py` | 647 | bpy · 入口 |
 | `osmassets/tree.py` | 318 | bpy |
 | `osmassets/geom.py` | 241 | 纯 |
-| `osmassets/materials.py` | 218 | bpy |
-| `osmassets/catalog.py` | 195 | 纯 |
+| `osmassets/materials.py` | 232 | bpy |
+| `osmassets/catalog.py` | 197 | 纯 |
 | `osmassets/mesh.py` | 126 | bpy |
 | `osmassets/osm.py` | 89 | 纯 |
+| `osmassets/building.py` / `fountain.py` | 56 / 49 | bpy |
 | `osmassets/water.py` / `grass.py` / `scrub.py` | 15 / 22 / 13 | bpy |
 | `tools/scene_digest.py` | 171 | bpy · 工具 |
 | `tests/test_pure.py` | 372 | 纯 · 测试 |
diff --git a/.trellis/spec/blender/module-structure.md b/.trellis/spec/blender/module-structure.md
index 89e1b0a..bdd79cd 100644
--- a/.trellis/spec/blender/module-structure.md
+++ b/.trellis/spec/blender/module-structure.md
@@ -24,7 +24,8 @@
      osmassets/mesh.py       MeshBatch、prism、polyline
      osmassets/materials.py  材质构建
      osmassets/tree.py       树实例化
-     osmassets/water.py  grass.py  scrub.py   要素装配
+     osmassets/water.py  grass.py  scrub.py
+     osmassets/building.py  fountain.py       要素装配
      generate_scene.py  export_cesium.py      两个入口脚本
      tools/scene_digest.py                    结构摘要工具
 ```
@@ -51,6 +52,7 @@
 | `materials.py` | bpy | 把 `catalog` 的规格变成真实材质：`from_spec()`、贴图、程序化噪声、tint、alpha-clip |
 | `tree.py` | bpy | 两个 vendored 模型 → 一套可实例化的运行时形状 |
 | `water.py` / `grass.py` / `scrub.py` | bpy | 单一 OSM 面要素的装配 |
+| `building.py` | bpy | 单一 OSM 面要素 `building=*` 的装配 |
 | `fountain.py` | bpy | 单一 OSM 点要素 `amenity=fountain` 的装配 |
 
 ### `geom.py` 的两条隐含约定
@@ -95,6 +97,20 @@ def assemble(name, x, y, collection, materials):
 创建三张 fountain 材质，并维护 `counts["fountain_count"]`。模块只负责在已投影
 坐标上创建 basin / water / pedestal / spray objects，保持对象名和自定义属性不变。
 
+`building.py` 是面要素模块，但不裁剪 ring；入口在调用前已经过滤
+`len(ring) >= 3`，并且建筑要保持原始 OSM footprint 参与相机取景：
+
+```python
+def assemble(ring, way_id, tag, office_overrides, collection, materials):
+    ...
+    return added, industrial_added, ring_pts
+```
+
+`generate_scene.py` 仍负责解析 `--office-overrides`、创建六张 building 材质、
+分发 `building=*` way、累加 `counts["building_count"]` /
+`counts["industrial_count"]`，以及写 `scene["office_override_way_ids"]`。
+模块只负责 prism / roof / windows / bevel / building custom properties。
+
 ### 加一种新 OSM 要素
 
 目标形态：**新增一个模块 + 注册一行，不改 `build()`**。
@@ -110,7 +126,7 @@ def assemble(name, x, y, collection, materials):
 
 ## 两个入口脚本
 
-| | `generate_scene.py` (999行) | `export_cesium.py` (624行) |
+| | `generate_scene.py` (899行) | `export_cesium.py` (647行) |
 |---|---|---|
 | 调用 | `--background --factory-startup --python` | `--background --python` |
 | 输入 | `--osm` + `--geojson` | `--blend` |
diff --git a/.trellis/spec/guides/artifact-parity-guide.md b/.trellis/spec/guides/artifact-parity-guide.md
index 45732cb..3dabe00 100644
--- a/.trellis/spec/guides/artifact-parity-guide.md
+++ b/.trellis/spec/guides/artifact-parity-guide.md
@@ -163,7 +163,7 @@ capturedAt / durationMs / label
 |---|---|---|
 | P0 | 抽纯函数到 `osmassets/{osm,geom}.py` | ✅ 已完成 |
 | P1 | `catalog.py` 单一定义源 + `check_layers` | ✅ 已完成 |
-| P2 | 要素注册表 | ⚠️ **部分**——`water/grass/scrub/tree/fountain.py` 已拆出，但**没有 `features/` 注册表**，`building` / `roads` 仍在 `generate_scene.py` 里 |
+| P2 | 要素注册表 | ⚠️ **部分**——`water/grass/scrub/tree/fountain/building.py` 已拆出，但**没有 `features/` 注册表**，`roads` 仍在 `generate_scene.py` 里 |
 | P3 | 材质契约化（自定义属性传递 spec） | ✅ 已完成——`catalog.MATERIALS[*]["cesium"]` 经 `materials.from_spec()` 写入 `material["cesium_export"]`，`export_cesium.py` 优先读该属性；四张材质名表仅作旧 `.blend` 回退 |
 
 ### 已知缺陷（记录在案，本轮不修）
diff --git a/.trellis/tasks/08-03-extract-building-module/check.jsonl b/.trellis/tasks/08-03-extract-building-module/check.jsonl
new file mode 100644
index 0000000..aaa7c65
--- /dev/null
+++ b/.trellis/tasks/08-03-extract-building-module/check.jsonl
@@ -0,0 +1,3 @@
+{"file": ".trellis/spec/blender/testing.md", "reason": "Defines pure test command and bpy-layer parity expectations for validation."}
+{"file": ".trellis/spec/guides/artifact-parity-guide.md", "reason": "Defines compare contract and expected no-diff result for refactors."}
+{"file": ".trellis/spec/blender/module-structure.md", "reason": "Defines dependency direction and safe import boundaries to review after new module creation."}
diff --git a/.trellis/tasks/08-03-extract-building-module/design.md b/.trellis/tasks/08-03-extract-building-module/design.md
new file mode 100644
index 0000000..353de1d
--- /dev/null
+++ b/.trellis/tasks/08-03-extract-building-module/design.md
@@ -0,0 +1,68 @@
+# Design
+
+## Architecture
+
+`building.py` will join the bpy-layer feature modules under
+`blender/osmassets/`. It may import `MeshBatch`, `add_roof`,
+`add_wall_panel`, and `make_prism` from `osmassets.mesh`, plus
+`parse_height` from `osmassets.osm`.
+
+The module will expose:
+
+```python
+def assemble(ring, way_id, tag, office_overrides, collection, materials):
+    ...
+```
+
+The function returns:
+
+```python
+(added, industrial_added, ring_pts)
+```
+
+This keeps `generate_scene.py`'s count and focus-point handling unchanged while
+removing building geometry construction from the entry script.
+
+## Boundaries
+
+- `generate_scene.py` keeps CLI parsing, OSM way dispatch, material creation,
+  count accumulation, focus-point accumulation, scene custom properties, and
+  stdout markers.
+- `building.py` owns only building object creation and building-specific facade
+  details for a ring that has already been projected.
+- `building.py` is a bpy-layer module. It must not be imported by pure Python
+  modules or pure unit tests.
+- `catalog.py` remains the material declaration source; no material entries or
+  order change in this task.
+
+## Data Flow
+
+1. `generate_scene.py` parses `args["office_overrides"]` into a set.
+2. `generate_scene.py` creates `building_mats` from `catalog.MATERIALS`.
+3. OSM ways are projected to local-meter rings in `generate_scene.py`.
+4. For ways with a `building` tag and at least three ring points,
+   `building.assemble(ring, str(way["id"]), tag, args["office_overrides"],
+   buildings_c, building_mats)` creates the prism, roof, windows, custom
+   properties, and bevel.
+5. `generate_scene.py` updates `counts["building_count"]`,
+   `counts["industrial_count"]`, and `focus_points` from the return tuple.
+
+## Compatibility
+
+The move must preserve object names, mesh names, material assignments, bevel
+modifier fields, custom properties, window-band geometry, and return values.
+Cesium export consumes the resulting `.blend`, so parity should see no
+non-ignored contract difference.
+
+## Trade-Offs
+
+The `office_overrides` set is passed into `building.assemble()` rather than
+passing the whole `args` dict. This narrows the module contract while preserving
+behavior. A full feature registry remains deferred until building and roads are
+both isolated enough to compare safely.
+
+## Rollback
+
+Rollback is mechanical: move `assemble()` and its helper back into
+`generate_scene.py`, restore direct calls, remove the `building.py` import, and
+delete the module.
diff --git a/.trellis/tasks/08-03-extract-building-module/implement.jsonl b/.trellis/tasks/08-03-extract-building-module/implement.jsonl
new file mode 100644
index 0000000..b8c1ba2
--- /dev/null
+++ b/.trellis/tasks/08-03-extract-building-module/implement.jsonl
@@ -0,0 +1,3 @@
+{"file": ".trellis/spec/blender/module-structure.md", "reason": "Defines bpy-layer module boundaries and feature module responsibilities for moving building assembly."}
+{"file": ".trellis/spec/blender/asset-generation.md", "reason": "Defines MeshBatch, material order, deterministic generation, and Cesium material constraints relevant to building assembly."}
+{"file": ".trellis/spec/guides/artifact-parity-guide.md", "reason": "Defines mandatory before/after parity validation for pure Blender scene refactors."}
diff --git a/.trellis/tasks/08-03-extract-building-module/implement.md b/.trellis/tasks/08-03-extract-building-module/implement.md
new file mode 100644
index 0000000..ed31bbf
--- /dev/null
+++ b/.trellis/tasks/08-03-extract-building-module/implement.md
@@ -0,0 +1,47 @@
+# Implementation Plan
+
+## Checklist
+
+1. Capture a parity baseline before product-code edits.
+2. Add `blender/osmassets/building.py` with the current building assembly and
+   detail helper logic.
+3. Import `building.py` in `blender/generate_scene.py`.
+4. Remove inline `_assemble_building()` and `add_building_details()` from
+   `generate_scene.py`.
+5. Replace the building call site with `building.assemble(...)`, passing
+   `args["office_overrides"]` instead of the full `args` dict.
+6. Run Python validation:
+   - `python3 -m py_compile blender/osmassets/building.py`
+   - `python3 -m py_compile blender/generate_scene.py`
+   - `python3 -m unittest blender/tests/test_pure.py`
+7. Capture parity after the refactor.
+8. Compare before/after parity snapshots and inspect any non-ignored diff.
+9. Update `.trellis/spec` and `docs/changelog.md` only for durable status or
+   convention changes discovered during implementation.
+10. Commit, archive the task, and record the journal entry.
+
+## Validation Commands
+
+```bash
+node scripts/parity.js capture building-module-before --stages blender,cesium
+python3 -m py_compile blender/osmassets/building.py
+python3 -m py_compile blender/generate_scene.py
+python3 -m unittest blender/tests/test_pure.py
+node scripts/parity.js capture building-module-after --stages blender,cesium
+node scripts/parity.js compare building-module-before building-module-after
+```
+
+## Risk Points
+
+- Passing `office_overrides` instead of `args` changes the function contract;
+  verify `office_override` custom properties and industrial classification via
+  parity.
+- `Building_<way_id>_Windows` mesh construction depends on `MeshBatch` object
+  naming and `add_wall_panel()` geometry; copy it mechanically.
+- `make_prism()` can return `None` on degenerate input, but the current call
+  site filters `len(ring) >= 3`. Preserve the existing behavior and return
+  tuple shape.
+- Do not reorder building material creation or catalog entries; material order
+  affects GLB material indices.
+- Parity is mandatory because this is a pure refactor of bpy-layer scene
+  generation.
diff --git a/.trellis/tasks/08-03-extract-building-module/prd.md b/.trellis/tasks/08-03-extract-building-module/prd.md
new file mode 100644
index 0000000..950e3fc
--- /dev/null
+++ b/.trellis/tasks/08-03-extract-building-module/prd.md
@@ -0,0 +1,93 @@
+# Extract building module
+
+## Goal
+
+Move building assembly out of `blender/generate_scene.py` into a dedicated
+bpy-layer module, keeping generated `.blend` / `.glb` / metadata structure
+unchanged. This continues the documented P2 feature-module direction after
+`fountain.py`.
+
+## Background
+
+- `.trellis/spec/guides/artifact-parity-guide.md` records P2 as partial:
+  `water.py`, `grass.py`, `scrub.py`, `tree.py`, and `fountain.py` are already
+  split out, while `building` and `roads` still live in `generate_scene.py`.
+- `blender/generate_scene.py:72` defines `_assemble_building()`.
+- `blender/generate_scene.py:179` defines `add_building_details()`, which
+  creates office / industrial window bands with `MeshBatch` and
+  `add_wall_panel()`.
+- `blender/generate_scene.py:789` dispatches OSM ways with a `building` tag,
+  increments `counts["building_count"]` and `counts["industrial_count"]`, and
+  extends `focus_points` with the returned ring.
+- `blender/generate_scene.py:710` creates `building_mats` from the existing
+  `catalog.MATERIALS["building_" + key]` entries.
+- `blender/generate_scene.py:910` persists `office_override_way_ids` as a scene
+  custom property from `args["office_overrides"]`.
+
+## Requirements
+
+1. Add a new bpy-layer module at `blender/osmassets/building.py`.
+2. Move the current building assembly behavior into the new module:
+   - `_assemble_building()`
+   - `add_building_details()`
+3. Expose an `assemble(...)` function from the new module that returns the same
+   tuple shape currently returned by `_assemble_building()`:
+   `(added, industrial_added, ring_pts)`.
+4. Keep `generate_scene.py` responsible for:
+   - parsing `--office-overrides`;
+   - creating `building_mats`;
+   - filtering OSM ways with a `building` tag and `len(ring) >= 3`;
+   - updating `building_count`, `industrial_count`, and `focus_points`;
+   - writing `scene["office_override_way_ids"]`;
+   - writing the existing `SCENE_DONE` JSON shape.
+5. Preserve existing building object names and mesh names:
+   - `Building_<way_id>`
+   - `Building_<way_id>_Roof`
+   - `Building_<way_id>_Windows`
+6. Preserve existing building custom properties:
+   - `osm_height`
+   - `render_height`
+   - `building_kind`
+   - `osm_building_tag`
+   - `office_override`
+7. Preserve current height rules:
+   - industrial buildings use the parsed source height;
+   - non-industrial buildings under 30m render at 11.4m;
+   - source height has a 3.0m floor and `parse_height(tag, 12.0)` default.
+8. Preserve current facade behavior:
+   - industrial buildings use one high horizontal band;
+   - office buildings use floor-based window bands;
+   - bevel modifier name, width, and segment count stay unchanged.
+9. Do not introduce a full `features/` registry in this task.
+10. Do not modify roads, material definitions, `MATERIALS` order,
+    `ROAD_LAYERS` order, stdout markers, parity ignore lists, or known
+    unrelated defects D1-D3.
+
+## Acceptance Criteria
+
+- [x] `blender/osmassets/building.py` contains building assembly behavior and
+      imports only bpy-layer-safe dependencies.
+- [x] `blender/generate_scene.py` imports and calls the new building module; no
+      inline `_assemble_building()` or `add_building_details()` remains there.
+- [x] Building counts, industrial counts, focus point behavior, scene custom
+      properties, and `SCENE_DONE` JSON keys remain unchanged.
+- [x] `python3 -m py_compile blender/osmassets/building.py` passes.
+- [x] `python3 -m py_compile blender/generate_scene.py` passes.
+- [x] `python3 -m unittest blender/tests/test_pure.py` passes.
+- [x] A before/after parity comparison is run for the Blender/Cesium stages and
+      any non-ignored diff is either absent or explicitly explained as
+      expected. For this refactor, the expected result is no contract diff.
+
+## Out Of Scope
+
+- Full feature registry implementation.
+- Road extraction.
+- Building visual redesign.
+- Building material or Cesium export contract changes.
+- Moving CLI parsing or `office_override_way_ids` scene metadata out of
+  `generate_scene.py`.
+- Changing geometry helper APIs in `osmassets.mesh`.
+
+## Open Questions
+
+None.
diff --git a/.trellis/tasks/08-03-extract-building-module/task.json b/.trellis/tasks/08-03-extract-building-module/task.json
new file mode 100644
index 0000000..e1bea36
--- /dev/null
+++ b/.trellis/tasks/08-03-extract-building-module/task.json
@@ -0,0 +1,26 @@
+{
+  "id": "extract-building-module",
+  "name": "extract-building-module",
+  "title": "Extract building module",
+  "description": "Move building assembly out of blender/generate_scene.py into a dedicated bpy-layer module without changing generated artifacts.",
+  "status": "in_progress",
+  "dev_type": null,
+  "scope": null,
+  "package": null,
+  "priority": "P2",
+  "creator": "dingkang",
+  "assignee": "dingkang",
+  "createdAt": "2026-08-03",
+  "completedAt": null,
+  "branch": null,
+  "base_branch": "main",
+  "worktree_path": null,
+  "commit": null,
+  "pr_url": null,
+  "subtasks": [],
+  "children": [],
+  "parent": null,
+  "relatedFiles": [],
+  "notes": "",
+  "meta": {}
+}
\ No newline at end of file
diff --git a/blender/generate_scene.py b/blender/generate_scene.py
index 65a79d0..030b9f3 100644
--- a/blender/generate_scene.py
+++ b/blender/generate_scene.py
@@ -52,12 +52,10 @@ from osmassets.materials import (  # noqa: E402
 from osmassets.mesh import (  # noqa: E402
     MeshBatch,
     add_polyline,
-    add_roof,
-    add_wall_panel,
-    make_prism,
     new_collection,
 )
 from osmassets.osm import Projector, parse_height, parse_osm  # noqa: E402
+from osmassets import building as _building  # noqa: E402
 from osmassets import fountain as _fountain  # noqa: E402
 from osmassets import water as _water  # noqa: E402
 from osmassets import grass as _grass  # noqa: E402
@@ -65,35 +63,6 @@ from osmassets import scrub as _scrub  # noqa: E402
 from osmassets import tree as _tree  # noqa: E402
 
 
-# Building assembly stays in this file because it needs make_prism, add_roof,
-# add_wall_panel, and add_building_details — Blender geometry helpers that
-# live a few lines above.  The other feature assembly code lives under
-# osmassets/ and keeps build() focused on data dispatch, materials, and counts.
-def _assemble_building(ring, way_id, tag, args, buildings_c, building_mats):
-    industrial = (tag.get("building") == "industrial" and
-                  way_id not in args["office_overrides"])
-    source_height = max(3.0, parse_height(tag, 12.0))
-    height = source_height if industrial or source_height >= 30.0 else 11.4
-    material = building_mats["industrial"] if industrial else building_mats["default"]
-    building_name = "Building_" + way_id
-    building_obj = make_prism(building_name, ring, 0.08, height,
-                              material, buildings_c)
-    if building_obj:
-        building_obj["osm_height"] = source_height
-        building_obj["render_height"] = height
-        building_obj["building_kind"] = "industrial" if industrial else "office"
-        building_obj["osm_building_tag"] = tag.get("building", "")
-        building_obj["office_override"] = way_id in args["office_overrides"]
-        bevel = building_obj.modifiers.new("Soft facade edges", "BEVEL")
-        bevel.width = 0.16
-        bevel.segments = 2
-    roof_mat = (building_mats["industrial_roof"] if industrial
-                else building_mats["office_roof"])
-    add_roof(building_name, ring, height + 0.095, roof_mat, buildings_c)
-    add_building_details(building_name, ring, height, industrial,
-                         building_mats, buildings_c)
-    return 1, int(industrial), ring
-
 MODEL_ROOT = os.path.abspath(os.path.join(
     os.path.dirname(__file__), "..", "assets", "models", "polyhaven"
 ))
@@ -176,34 +145,6 @@ def cli_args():
     return values
 
 
-def add_building_details(name, ring, height, industrial, materials, collection):
-    footprint = ring[:-1] if len(ring) > 1 and ring[0] == ring[-1] else ring
-    if len(footprint) < 3:
-        return
-    glass_mat = materials["factory_glass"] if industrial else materials["glass"]
-
-    glass_batch = MeshBatch(name + "_Windows", collection, glass_mat)
-    edges = list(zip(footprint, footprint[1:] + footprint[:1]))
-    if industrial:
-        band_height = min(1.8, max(0.75, height * 0.16))
-        band_base = max(0.9, height * 0.52)
-        for start, end in edges:
-            add_wall_panel(glass_batch, start, end, band_base, band_height,
-                           thickness=0.055, inset=0.12)
-    else:
-        floor_height = 3.25
-        floor_count = max(1, int((height - 0.7) / floor_height))
-        for floor in range(floor_count):
-            band_base = 0.55 + floor * floor_height + 0.95
-            if band_base + 1.25 > height - 0.18:
-                break
-            for start, end in edges:
-                add_wall_panel(glass_batch, start, end, band_base, 1.25,
-                               thickness=0.045, inset=0.10)
-    glass_batch.finish()
-
-
-
 def add_geojson_layer(path, layer, projector, collection, material, z):
     if not os.path.exists(path):
         return 0
@@ -787,8 +728,9 @@ def build(args):
             tree_rows.append((ring, tag))
             focus_points.extend(ring)
         elif "building" in tag and len(ring) >= 3:
-            added, ind_added, ring_pts = _assemble_building(
-                ring, str(way["id"]), tag, args, buildings_c, building_mats)
+            added, ind_added, ring_pts = _building.assemble(
+                ring, str(way["id"]), tag, args["office_overrides"],
+                buildings_c, building_mats)
             counts["building_count"] += added
             counts["industrial_count"] += ind_added
             if ring_pts:
diff --git a/blender/osmassets/building.py b/blender/osmassets/building.py
new file mode 100644
index 0000000..93e4a51
--- /dev/null
+++ b/blender/osmassets/building.py
@@ -0,0 +1,56 @@
+"""Building feature assembly (`building=*`)."""
+
+from osmassets.mesh import MeshBatch, add_roof, add_wall_panel, make_prism
+from osmassets.osm import parse_height
+
+
+def add_details(name, ring, height, industrial, materials, collection):
+    footprint = ring[:-1] if len(ring) > 1 and ring[0] == ring[-1] else ring
+    if len(footprint) < 3:
+        return
+    glass_mat = materials["factory_glass"] if industrial else materials["glass"]
+
+    glass_batch = MeshBatch(name + "_Windows", collection, glass_mat)
+    edges = list(zip(footprint, footprint[1:] + footprint[:1]))
+    if industrial:
+        band_height = min(1.8, max(0.75, height * 0.16))
+        band_base = max(0.9, height * 0.52)
+        for start, end in edges:
+            add_wall_panel(glass_batch, start, end, band_base, band_height,
+                           thickness=0.055, inset=0.12)
+    else:
+        floor_height = 3.25
+        floor_count = max(1, int((height - 0.7) / floor_height))
+        for floor in range(floor_count):
+            band_base = 0.55 + floor * floor_height + 0.95
+            if band_base + 1.25 > height - 0.18:
+                break
+            for start, end in edges:
+                add_wall_panel(glass_batch, start, end, band_base, 1.25,
+                               thickness=0.045, inset=0.10)
+    glass_batch.finish()
+
+
+def assemble(ring, way_id, tag, office_overrides, collection, materials):
+    industrial = (tag.get("building") == "industrial" and
+                  way_id not in office_overrides)
+    source_height = max(3.0, parse_height(tag, 12.0))
+    height = source_height if industrial or source_height >= 30.0 else 11.4
+    material = materials["industrial"] if industrial else materials["default"]
+    building_name = "Building_" + way_id
+    building_obj = make_prism(building_name, ring, 0.08, height,
+                              material, collection)
+    if building_obj:
+        building_obj["osm_height"] = source_height
+        building_obj["render_height"] = height
+        building_obj["building_kind"] = "industrial" if industrial else "office"
+        building_obj["osm_building_tag"] = tag.get("building", "")
+        building_obj["office_override"] = way_id in office_overrides
+        bevel = building_obj.modifiers.new("Soft facade edges", "BEVEL")
+        bevel.width = 0.16
+        bevel.segments = 2
+    roof_mat = (materials["industrial_roof"] if industrial
+                else materials["office_roof"])
+    add_roof(building_name, ring, height + 0.095, roof_mat, collection)
+    add_details(building_name, ring, height, industrial, materials, collection)
+    return 1, int(industrial), ring
diff --git a/docs/changelog.md b/docs/changelog.md
index 1f8b051..eda6c54 100644
--- a/docs/changelog.md
+++ b/docs/changelog.md
@@ -18,6 +18,10 @@
   保留点要素过滤、投影、材质创建和计数。Blender/Cesium parity before/after 在
   `nantaizi-lake-innovation-valley` 与 `hanyang-block` 两个样本上均 identical；P2
   剩余未拆出部分更新为 `building` / `roads`。
+- 抽出 building 要素装配：新增 `blender/osmassets/building.py`，迁移 building prism、
+  roof、window bands、bevel 和 building custom properties；`generate_scene.py` 继续
+  负责 `office_overrides`、材质创建、way 分发、计数和 scene metadata。Blender/Cesium
+  parity before/after 在两个样本上均 identical；P2 剩余未拆出部分更新为 `roads`。
 
 ## 2026-07-31（三）远看发黑的真正原因：反照率没被提亮