diff --git a/orchestration/modelling_orchestrator.py b/orchestration/modelling_orchestrator.py
index 7a30d7e82..23ac42941 100644
--- a/orchestration/modelling_orchestrator.py
+++ b/orchestration/modelling_orchestrator.py
@@ -19,6 +19,7 @@ from domain.modelling.optimisation.optimiser import (
     OptimisedPackage,
     ScoredOption,
     optimise_package,
+    optimise_package_fabric_first,
 )
 from domain.modelling.scoring.package_scorer import PackageScorer, Score
 from domain.modelling.plan import Plan, PlanMeasure
@@ -188,7 +189,13 @@ class ModellingOrchestrator:
         dependencies: list[MeasureDependency] = _measure_dependencies(
             effective_epc, products, considered
         )
-        package: OptimisedPackage = optimise_package(
+        # A Fabric First brief optimises the envelope with the full budget
+        # before heating / renewables are considered on top (mirroring the
+        # legacy engine's enforce_fabric_first).
+        optimise = (
+            optimise_package_fabric_first if scenario.fabric_first else optimise_package
+        )
+        package: OptimisedPackage = optimise(
             groups=groups,
             scorer=scorer,
             baseline_epc=effective_epc,