diff --git a/applications/audit-generator/handler.py b/applications/audit-generator/handler.py
index e69de29b..6ad89ccb 100644
--- a/applications/audit-generator/handler.py
+++ b/applications/audit-generator/handler.py
@@ -0,0 +1 @@
+from applications.audit_generator.handler import handler  # noqa: F401
diff --git a/applications/audit-generator/handler/audit_generator_trigger_request.py b/applications/audit-generator/handler/audit_generator_trigger_request.py
index e69de29b..165a8e6c 100644
--- a/applications/audit-generator/handler/audit_generator_trigger_request.py
+++ b/applications/audit-generator/handler/audit_generator_trigger_request.py
@@ -0,0 +1 @@
+from applications.audit_generator.audit_generator_trigger_request import AuditGeneratorTriggerRequest  # noqa: F401
diff --git a/applications/audit_generator/__init__.py b/applications/audit_generator/__init__.py
new file mode 100644
index 00000000..e69de29b
diff --git a/applications/audit_generator/audit_generator_trigger_request.py b/applications/audit_generator/audit_generator_trigger_request.py
new file mode 100644
index 00000000..042db001
--- /dev/null
+++ b/applications/audit_generator/audit_generator_trigger_request.py
@@ -0,0 +1,9 @@
+from pydantic import BaseModel, ConfigDict
+
+
+class AuditGeneratorTriggerRequest(BaseModel):
+    model_config = ConfigDict(extra="ignore")
+
+    task_id: str
+    sub_task_id: str
+    hubspot_deal_id: str
diff --git a/applications/audit_generator/handler.py b/applications/audit_generator/handler.py
new file mode 100644
index 00000000..b560f808
--- /dev/null
+++ b/applications/audit_generator/handler.py
@@ -0,0 +1,40 @@
+from __future__ import annotations
+
+import os
+from typing import Any
+
+import boto3
+
+from applications.audit_generator.audit_generator_trigger_request import (
+    AuditGeneratorTriggerRequest,
+)
+from infrastructure.postgres.config import PostgresConfig
+from infrastructure.postgres.engine import make_engine, make_session
+from infrastructure.s3.s3_client import S3Client
+from orchestration.audit_generator_orchestrator import AuditGeneratorOrchestrator
+from orchestration.audit_generator_unit_of_work import AuditGeneratorUnitOfWork
+from utilities.aws_lambda.subtask_handler import subtask_handler
+
+_engine = make_engine(PostgresConfig.from_env(os.environ))
+
+
+@subtask_handler()
+def handler(body: dict[str, Any], context: Any) -> None:
+    trigger = AuditGeneratorTriggerRequest.model_validate(body)
+
+    boto3_client: Any = boto3.client  # pyright: ignore[reportUnknownMemberType, reportUnknownVariableType]
+    boto_s3: Any = boto3_client("s3")
+    bucket = os.environ["S3_BUCKET_NAME"]
+    s3_client = S3Client(boto_s3_client=boto_s3, bucket=bucket)
+
+    def session_factory() -> Any:
+        return make_session(_engine)
+
+    def uow_factory() -> AuditGeneratorUnitOfWork:
+        return AuditGeneratorUnitOfWork(session_factory)
+
+    AuditGeneratorOrchestrator(
+        hubspot_deal_id=trigger.hubspot_deal_id,
+        s3_client=s3_client,
+        uow_factory=uow_factory,
+    ).run()
diff --git a/orchestration/audit_generator_orchestrator.py b/orchestration/audit_generator_orchestrator.py
new file mode 100644
index 00000000..887f0092
--- /dev/null
+++ b/orchestration/audit_generator_orchestrator.py
@@ -0,0 +1,24 @@
+from __future__ import annotations
+
+from collections.abc import Callable
+from typing import TYPE_CHECKING
+
+from infrastructure.s3.s3_client import S3Client
+
+if TYPE_CHECKING:
+    from orchestration.audit_generator_unit_of_work import AuditGeneratorUnitOfWork
+
+
+class AuditGeneratorOrchestrator:
+    def __init__(
+        self,
+        hubspot_deal_id: str,
+        s3_client: S3Client,
+        uow_factory: Callable[[], "AuditGeneratorUnitOfWork"],
+    ) -> None:
+        self._hubspot_deal_id = hubspot_deal_id
+        self._s3_client = s3_client
+        self._uow_factory = uow_factory
+
+    def run(self) -> None:
+        raise NotImplementedError
diff --git a/orchestration/audit_generator_unit_of_work.py b/orchestration/audit_generator_unit_of_work.py
new file mode 100644
index 00000000..694d6039
--- /dev/null
+++ b/orchestration/audit_generator_unit_of_work.py
@@ -0,0 +1,39 @@
+from __future__ import annotations
+
+from collections.abc import Callable
+from types import TracebackType
+from typing import Optional
+
+from sqlmodel import Session
+
+from repositories.magic_plan.magic_plan_postgres_repository import (
+    MagicPlanPostgresRepository,
+)
+from repositories.uploaded_file.uploaded_file_postgres_repository import (
+    UploadedFilePostgresRepository,
+)
+
+
+class AuditGeneratorUnitOfWork:
+    def __init__(self, session_factory: Callable[[], Session]) -> None:
+        self._session_factory = session_factory
+
+    def __enter__(self) -> "AuditGeneratorUnitOfWork":
+        self._session = self._session_factory()
+        self.uploaded_file = UploadedFilePostgresRepository(self._session)
+        self.magic_plan = MagicPlanPostgresRepository(self._session)
+        return self
+
+    def __exit__(
+        self,
+        exc_type: Optional[type[BaseException]],
+        exc: Optional[BaseException],
+        tb: Optional[TracebackType],
+    ) -> None:
+        try:
+            self._session.rollback()
+        finally:
+            self._session.close()
+
+    def commit(self) -> None:
+        self._session.commit()
diff --git a/tests/applications/audit_generator/__init__.py b/tests/applications/audit_generator/__init__.py
new file mode 100644
index 00000000..e69de29b
diff --git a/tests/applications/audit_generator/test_audit_generator_handler.py b/tests/applications/audit_generator/test_audit_generator_handler.py
new file mode 100644
index 00000000..f9bc74b6
--- /dev/null
+++ b/tests/applications/audit_generator/test_audit_generator_handler.py
@@ -0,0 +1,94 @@
+from __future__ import annotations
+
+from typing import Any
+from unittest.mock import MagicMock, patch
+
+import pytest
+from pydantic import ValidationError
+
+from applications.audit_generator.handler import handler
+
+_ENV = {
+    "DATABASE_URL": "postgresql+psycopg://user:pass@localhost/db",
+    "S3_BUCKET_NAME": "test-bucket",
+    # PostgresConfig.from_env also reads these individual vars; DATABASE_URL is
+    # used directly when constructing the engine in the handler module scope, so
+    # we patch make_engine instead of the env.
+}
+
+_VALID_BODY: dict[str, Any] = {
+    "task_id": "task-1",
+    "sub_task_id": "subtask-1",
+    "hubspot_deal_id": "deal-xyz",
+}
+
+
+def _call(body: dict[str, Any]) -> Any:
+    return handler.__wrapped__(body, None)  # type: ignore[attr-defined]
+
+
+# --- request validation ---
+
+
+def test_invalid_body_raises_validation_error() -> None:
+    # Arrange — body missing all required fields
+    body: dict[str, Any] = {}
+
+    # Act / Assert
+    with patch("applications.audit_generator.handler.AuditGeneratorOrchestrator"):
+        with pytest.raises(ValidationError):
+            _call(body)
+
+
+# --- orchestrator construction ---
+
+
+def test_handler_passes_hubspot_deal_id_from_body_to_orchestrator() -> None:
+    # Arrange
+    mock_orch = MagicMock()
+    mock_orch.run.return_value = None
+
+    # Act
+    with patch("applications.audit_generator.handler.os.environ", _ENV), \
+         patch("applications.audit_generator.handler.S3Client") as MockS3, \
+         patch("applications.audit_generator.handler.AuditGeneratorOrchestrator", return_value=mock_orch) as MockOrch:
+        MockS3.return_value = MagicMock()
+        _call(_VALID_BODY)
+
+    # Assert — deal id flows from body into the orchestrator constructor
+    MockOrch.assert_called_once()
+    assert MockOrch.call_args.kwargs["hubspot_deal_id"] == "deal-xyz"
+
+
+def test_handler_passes_bucket_from_env_to_s3_client() -> None:
+    # Arrange
+    mock_orch = MagicMock()
+    mock_orch.run.return_value = None
+
+    # Act
+    with patch("applications.audit_generator.handler.os.environ", _ENV), \
+         patch("applications.audit_generator.handler.S3Client") as MockS3, \
+         patch("applications.audit_generator.handler.AuditGeneratorOrchestrator", return_value=mock_orch):
+        _call(_VALID_BODY)
+
+    # Assert — bucket name from env reaches S3Client constructor
+    MockS3.assert_called_once()
+    assert MockS3.call_args.kwargs["bucket"] == "test-bucket"
+
+
+# --- return value ---
+
+
+def test_handler_returns_none_on_success() -> None:
+    # Arrange
+    mock_orch = MagicMock()
+    mock_orch.run.return_value = None
+
+    # Act
+    with patch("applications.audit_generator.handler.os.environ", _ENV), \
+         patch("applications.audit_generator.handler.S3Client"), \
+         patch("applications.audit_generator.handler.AuditGeneratorOrchestrator", return_value=mock_orch):
+        result = _call(_VALID_BODY)
+
+    # Assert
+    assert result is None
diff --git a/tests/orchestration/audit_generator/__init__.py b/tests/orchestration/audit_generator/__init__.py
new file mode 100644
index 00000000..e69de29b
diff --git a/tests/orchestration/audit_generator/test_audit_generator_orchestrator.py b/tests/orchestration/audit_generator/test_audit_generator_orchestrator.py
new file mode 100644
index 00000000..18445fe5
--- /dev/null
+++ b/tests/orchestration/audit_generator/test_audit_generator_orchestrator.py
@@ -0,0 +1,219 @@
+from __future__ import annotations
+
+from io import BytesIO
+from typing import Any
+from unittest.mock import MagicMock, call, patch
+
+import pytest
+
+from domain.magicplan.models import (
+    Door,
+    DoorVentilation,
+    Floor,
+    Plan,
+    Room,
+    Window,
+    WindowVentilation,
+)
+from infrastructure.postgres.uploaded_file_table import (
+    FileSourceEnum,
+    FileTypeEnum,
+    UploadedFile,
+)
+from infrastructure.s3.s3_client import S3Client
+from orchestration.audit_generator_orchestrator import AuditGeneratorOrchestrator
+
+_DEAL_ID = "deal-abc"
+_BUCKET = "test-bucket"
+_EXPECTED_S3_KEY = f"documents/hubspot_deal_id/{_DEAL_ID}/ventilation_audit.xlsx"
+
+
+def _make_window(with_ventilation: bool = True) -> Window:
+    vent = (
+        WindowVentilation(
+            opening_type="Hinged",
+            num_openings=1,
+            pct_openable=50,
+            trickle_vent_area_mm2=1000,
+            num_trickle_vents=2,
+        )
+        if with_ventilation
+        else None
+    )
+    return Window(width_m=1.0, height_m=1.2, area_m2=1.2, ventilation=vent)
+
+
+def _make_door(with_ventilation: bool = True) -> Door:
+    vent = DoorVentilation(undercut_mm=10.0) if with_ventilation else None
+    return Door(width_mm=800.0, height_mm=2000.0, ventilation=vent)
+
+
+def _make_plan(
+    num_rooms: int = 1,
+    num_windows_per_room: int = 1,
+    num_doors_per_room: int = 1,
+) -> Plan:
+    rooms = [
+        Room(
+            name=f"Room {i}",
+            width_m=3.0,
+            length_m=4.0,
+            area_m2=12.0,
+            windows=[_make_window() for _ in range(num_windows_per_room)],
+            doors=[_make_door() for _ in range(num_doors_per_room)],
+        )
+        for i in range(num_rooms)
+    ]
+    return Plan(
+        uid="test-uid",
+        name="Test Plan",
+        address="1 Test St",
+        postcode="TE1 1ST",
+        floors=[Floor(level=0, name="Ground", rooms=rooms)],
+    )
+
+
+def _make_uploaded_file_row(id: int = 1) -> UploadedFile:
+    return UploadedFile(
+        id=id,
+        s3_file_bucket=_BUCKET,
+        s3_file_key="documents/deal/plan.json",
+        s3_upload_timestamp=None,  # type: ignore[arg-type]
+        hubspot_deal_id=_DEAL_ID,
+        file_type=FileTypeEnum.MAGIC_PLAN_JSON.value,
+    )
+
+
+def _make_mock_uow(
+    uploaded_file_row: Any = None,
+    plan: Any = None,
+) -> tuple[MagicMock, MagicMock]:
+    """Return (mock_uow, mock_uow_factory)."""
+    mock_uow = MagicMock()
+    mock_uow.__enter__ = MagicMock(return_value=mock_uow)
+    mock_uow.__exit__ = MagicMock(return_value=False)
+    mock_uow.uploaded_file.get_latest_by_hubspot_deal_id.return_value = uploaded_file_row
+    mock_uow.magic_plan.get_plan_by_uploaded_file_id.return_value = plan
+    mock_uow_factory = MagicMock(return_value=mock_uow)
+    return mock_uow, mock_uow_factory
+
+
+def _make_s3() -> MagicMock:
+    s3 = MagicMock(spec=S3Client)
+    s3.bucket = _BUCKET
+    return s3
+
+
+def _make_orchestrator(
+    s3: Any = None,
+    uow_factory: Any = None,
+    deal_id: str = _DEAL_ID,
+) -> AuditGeneratorOrchestrator:
+    return AuditGeneratorOrchestrator(
+        hubspot_deal_id=deal_id,
+        s3_client=s3 or _make_s3(),
+        uow_factory=uow_factory or MagicMock(),
+    )
+
+
+# --- error: no uploaded file ---
+
+
+def test_raises_when_no_magic_plan_json_uploaded() -> None:
+    # Arrange
+    mock_uow, mock_uow_factory = _make_mock_uow(uploaded_file_row=None)
+    orch = _make_orchestrator(uow_factory=mock_uow_factory)
+
+    # Act / Assert
+    with pytest.raises(ValueError, match="No MagicPlan"):
+        orch.run()
+
+
+# --- error: plan not yet parsed ---
+
+
+def test_raises_when_plan_not_yet_parsed() -> None:
+    # Arrange
+    mock_uow, mock_uow_factory = _make_mock_uow(
+        uploaded_file_row=_make_uploaded_file_row(), plan=None
+    )
+    orch = _make_orchestrator(uow_factory=mock_uow_factory)
+
+    # Act / Assert
+    with pytest.raises(ValueError, match="not yet parsed"):
+        orch.run()
+
+
+# --- happy path ---
+
+
+def test_uploads_to_correct_s3_key() -> None:
+    # Arrange
+    s3 = _make_s3()
+    plan = _make_plan()
+    mock_uow, mock_uow_factory = _make_mock_uow(
+        uploaded_file_row=_make_uploaded_file_row(), plan=plan
+    )
+    orch = _make_orchestrator(s3=s3, uow_factory=mock_uow_factory)
+
+    # Act
+    orch.run()
+
+    # Assert
+    s3.put_object.assert_called_once()
+    assert s3.put_object.call_args.args[0] == _EXPECTED_S3_KEY
+
+
+def test_inserts_uploaded_file_with_correct_enums() -> None:
+    # Arrange
+    plan = _make_plan()
+    mock_uow, mock_uow_factory = _make_mock_uow(
+        uploaded_file_row=_make_uploaded_file_row(), plan=plan
+    )
+    orch = _make_orchestrator(uow_factory=mock_uow_factory)
+
+    # Act
+    orch.run()
+
+    # Assert — the UploadedFile inserted has the correct type/source
+    mock_uow.uploaded_file.insert.assert_called_once()
+    inserted: UploadedFile = mock_uow.uploaded_file.insert.call_args.args[0]
+    assert inserted.file_type == FileTypeEnum.VENTILATION_AUDIT.value
+    assert inserted.file_source == FileSourceEnum.AUDIT_GENERATOR.value
+    assert inserted.hubspot_deal_id == _DEAL_ID
+    assert inserted.s3_file_key == _EXPECTED_S3_KEY
+
+
+def test_commits_after_s3_upload() -> None:
+    # Arrange
+    s3 = _make_s3()
+    plan = _make_plan()
+    mock_uow, mock_uow_factory = _make_mock_uow(
+        uploaded_file_row=_make_uploaded_file_row(), plan=plan
+    )
+    call_order: list[str] = []
+    s3.put_object.side_effect = lambda *a, **kw: call_order.append("s3_upload")
+    mock_uow.commit.side_effect = lambda: call_order.append("commit")
+    orch = _make_orchestrator(s3=s3, uow_factory=mock_uow_factory)
+
+    # Act
+    orch.run()
+
+    # Assert — S3 upload happens before DB commit
+    assert call_order == ["s3_upload", "commit"]
+
+
+# --- 50-row limit ---
+
+
+def test_raises_when_series_exceeds_50_rows() -> None:
+    # Arrange — 51 windows, which exceeds the template limit
+    plan = _make_plan(num_rooms=1, num_windows_per_room=51)
+    mock_uow, mock_uow_factory = _make_mock_uow(
+        uploaded_file_row=_make_uploaded_file_row(), plan=plan
+    )
+    orch = _make_orchestrator(uow_factory=mock_uow_factory)
+
+    # Act / Assert
+    with pytest.raises(ValueError, match="50"):
+        orch.run()