diff --git a/domain/modelling/contingencies.py b/domain/modelling/contingencies.py
index 8d0230ff..d1e21357 100644
--- a/domain/modelling/contingencies.py
+++ b/domain/modelling/contingencies.py
@@ -10,6 +10,7 @@ _CONTINGENCY_RATES: dict[str, float] = {
     "loft_insulation": 0.10,
     "suspended_floor_insulation": 0.20,
     "solid_floor_insulation": 0.26,
+    "mechanical_ventilation": 0.26,
 }
 
 
diff --git a/orchestration/modelling_orchestrator.py b/orchestration/modelling_orchestrator.py
index da10f744..86939839 100644
--- a/orchestration/modelling_orchestrator.py
+++ b/orchestration/modelling_orchestrator.py
@@ -6,7 +6,9 @@ from typing import Final, Optional
 from datatypes.epc.domain.epc import Epc
 from datatypes.epc.domain.epc_property_data import EpcPropertyData
 from domain.modelling.floor_recommendation import recommend_floor_insulation
+from domain.modelling.measure_dependency import ventilation_dependency
 from domain.modelling.optimiser import (
+    MeasureDependency,
     OptimisedPackage,
     ScoredOption,
     optimise_package,
@@ -33,12 +35,15 @@ from repositories.unit_of_work import UnitOfWork
 _INCREASING_EPC_GOAL: Final[str] = "Increasing EPC"
 
 # Best-practice install sequence for the role-3 attribution cascade (ADR-0016):
-# fabric in walls → roof → floor order, per the legacy `Recommendations` class.
+# walls → roof → ventilation → floor, per the legacy `Recommendations` class.
+# Ventilation sits after the fabric that triggers it so its (negative) marginal
+# is attributed against the insulated envelope.
 _BEST_PRACTICE_ORDER: Final[tuple[str, ...]] = (
     "cavity_wall_insulation",
     "external_wall_insulation",
     "internal_wall_insulation",
     "loft_insulation",
+    "mechanical_ventilation",
     "suspended_floor_insulation",
     "solid_floor_insulation",
 )
@@ -106,12 +111,18 @@ class ModellingOrchestrator:
         groups: list[list[ScoredOption]] = _scored_candidate_groups(
             scorer, effective_epc, products
         )
+        # Forced Measure Dependencies (ventilation) are excluded from the pool
+        # but injected into the package before the re-score (ADR-0016).
+        dependencies: list[MeasureDependency] = _measure_dependencies(
+            effective_epc, products
+        )
         package: OptimisedPackage = optimise_package(
             groups=groups,
             scorer=scorer,
             baseline_epc=effective_epc,
             budget=scenario.budget,
             target_sap=_target_sap(scenario),
+            dependencies=dependencies,
         )
 
         # Role-3 attribution: re-apply the *selected* set in best-practice order
@@ -145,6 +156,18 @@ def _candidate_recommendations(
     return [recommendation for recommendation in found if recommendation is not None]
 
 
+def _measure_dependencies(
+    effective_epc: EpcPropertyData, products: ProductRepository
+) -> list[MeasureDependency]:
+    """The forced Measure Dependencies for this Property — currently just
+    ventilation, suppressed when the dwelling is already mechanically
+    ventilated (ADR-0016)."""
+    dependency: Optional[MeasureDependency] = ventilation_dependency(
+        effective_epc, products
+    )
+    return [dependency] if dependency is not None else []
+
+
 def _scored_candidate_groups(
     scorer: PackageScorer,
     effective_epc: EpcPropertyData,
diff --git a/tests/orchestration/test_ara_first_run_pipeline_integration.py b/tests/orchestration/test_ara_first_run_pipeline_integration.py
index 66791c1d..f4a0cf60 100644
--- a/tests/orchestration/test_ara_first_run_pipeline_integration.py
+++ b/tests/orchestration/test_ara_first_run_pipeline_integration.py
@@ -115,16 +115,28 @@ def test_first_run_baselines_through_repos_and_is_idempotent_on_rerun(
             )
         )
         # The sample EPC's solid floor is uninsulated, so the floor generator
-        # fires during candidate generation and prices against this Product.
-        session.add(
-            MaterialRow(
-                id=1,
-                type="solid_floor_insulation",
-                total_cost=25.0,
-                cost_unit="gbp_per_m2",
-                is_active=True,
-                description="Solid floor insulation",
-            )
+        # fires during candidate generation and prices against this Product. The
+        # ventilation Measure Dependency is built for every not-yet-ventilated
+        # dwelling, so its Product must exist too (ADR-0016).
+        session.add_all(
+            [
+                MaterialRow(
+                    id=1,
+                    type="solid_floor_insulation",
+                    total_cost=25.0,
+                    cost_unit="gbp_per_m2",
+                    is_active=True,
+                    description="Solid floor insulation",
+                ),
+                MaterialRow(
+                    id=2,
+                    type="mechanical_ventilation",
+                    total_cost=450.0,
+                    cost_unit="gbp_per_unit",
+                    is_active=True,
+                    description="Mechanical extract ventilation unit",
+                ),
+            ]
         )
         session.commit()
 
@@ -220,6 +232,14 @@ def test_modelling_optimises_and_persists_a_multi_measure_plan(
                     is_active=True,
                     description="Suspended floor insulation",
                 ),
+                MaterialRow(
+                    id=3,
+                    type="mechanical_ventilation",
+                    total_cost=450.0,
+                    cost_unit="gbp_per_unit",
+                    is_active=True,
+                    description="Mechanical extract ventilation unit",
+                ),
             ]
         )
         session.commit()
@@ -238,8 +258,9 @@ def test_modelling_optimises_and_persists_a_multi_measure_plan(
         unit_of_work=unit_of_work, calculator=Sap10Calculator()
     ).run(property_ids=[30], scenario_ids=[7], portfolio_id=1)
 
-    # Assert — one Plan with two Plan Measures (wall + floor), each priced and
-    # attributed, linked by plan_id.
+    # Assert — one Plan with three Plan Measures: the wall + floor the Optimiser
+    # chose, plus the ventilation Measure Dependency the wall forces in
+    # (ADR-0016). Each is priced and attributed, linked by plan_id.
     with Session(db_engine) as session:
         plan = session.exec(
             select(PlanRow).where(col(PlanRow.property_id) == 30)
@@ -259,14 +280,21 @@ def test_modelling_optimises_and_persists_a_multi_measure_plan(
     assert plan.cost_of_works is not None
     assert plan.cost_of_works > 0.0
 
-    measure_types = {rec.type for rec in rec_rows}
-    assert measure_types == {
+    by_type = {rec.type: rec for rec in rec_rows}
+    assert set(by_type) == {
         "cavity_wall_insulation",
         "suspended_floor_insulation",
+        "mechanical_ventilation",
     }
     for rec in rec_rows:
         assert rec.default is True
         assert rec.already_installed is False
         assert rec.sap_points is not None
         assert rec.estimated_cost is not None
-        assert rec.estimated_cost > 0.0
+    # The forced ventilation costs two £450 units and is priced even though it
+    # was never a free choice in the pool.
+    assert abs(by_type["mechanical_ventilation"].estimated_cost - 900.0) <= 1e-6
+    # The insulation measures earn positive SAP; ventilation's contribution is
+    # not positive (it only ever costs SAP — ADR-0016).
+    assert by_type["cavity_wall_insulation"].sap_points > 0.0
+    assert by_type["mechanical_ventilation"].sap_points <= 0.0