diff --git a/domain/modelling/floor_recommendation.py b/domain/modelling/floor_recommendation.py
index a6992a85..f2360677 100644
--- a/domain/modelling/floor_recommendation.py
+++ b/domain/modelling/floor_recommendation.py
@@ -21,6 +21,12 @@ from repositories.product.product_repository import ProductRepository
 
 # Recommended ground-floor insulation depth (mm).
 _RECOMMENDED_FLOOR_THICKNESS_MM = 100
+# Insulating an as-built floor re-lodges its insulation as retro-fitted. The
+# calculator keys on this for a suspended timber floor's sealed/unsealed
+# determination (cert_to_inputs: "retro" + no U-value → sealed), so the
+# overlay must set it or the suspended-floor cascade leaves a ~1.4 SAP gap
+# (see test_elmhurst_cascade_pins).
+_RETROFITTED_INSULATION = "Retro-fitted"
 
 
 def _is_uninsulated(thickness: Optional[Union[str, int]]) -> bool:
@@ -75,7 +81,8 @@ def recommend_floor_insulation(
         overlay=EpcSimulation(
             building_parts={
                 BuildingPartIdentifier.MAIN: BuildingPartOverlay(
-                    floor_insulation_thickness=_RECOMMENDED_FLOOR_THICKNESS_MM
+                    floor_insulation_thickness=_RECOMMENDED_FLOOR_THICKNESS_MM,
+                    floor_insulation_type_str=_RETROFITTED_INSULATION,
                 )
             }
         ),
diff --git a/domain/modelling/simulation.py b/domain/modelling/simulation.py
index 5b2ba8a6..7f9b7469 100644
--- a/domain/modelling/simulation.py
+++ b/domain/modelling/simulation.py
@@ -24,6 +24,7 @@ class BuildingPartOverlay:
     wall_insulation_type: Optional[int] = None
     roof_insulation_thickness: Optional[int] = None
     floor_insulation_thickness: Optional[int] = None
+    floor_insulation_type_str: Optional[str] = None
 
 
 def _no_building_parts() -> dict[BuildingPartIdentifier, BuildingPartOverlay]:
diff --git a/tests/domain/modelling/fixtures/solid_floor_001431_after.pdf b/tests/domain/modelling/fixtures/solid_floor_001431_after.pdf
new file mode 100644
index 00000000..ea3ffbfa
Binary files /dev/null and b/tests/domain/modelling/fixtures/solid_floor_001431_after.pdf differ
diff --git a/tests/domain/modelling/fixtures/solid_floor_001431_before.pdf b/tests/domain/modelling/fixtures/solid_floor_001431_before.pdf
new file mode 100644
index 00000000..187140c0
Binary files /dev/null and b/tests/domain/modelling/fixtures/solid_floor_001431_before.pdf differ
diff --git a/tests/domain/modelling/fixtures/suspended_floor_001431_after.pdf b/tests/domain/modelling/fixtures/suspended_floor_001431_after.pdf
new file mode 100644
index 00000000..3cc53118
Binary files /dev/null and b/tests/domain/modelling/fixtures/suspended_floor_001431_after.pdf differ
diff --git a/tests/domain/modelling/fixtures/suspended_floor_001431_before.pdf b/tests/domain/modelling/fixtures/suspended_floor_001431_before.pdf
new file mode 100644
index 00000000..49a82bc0
Binary files /dev/null and b/tests/domain/modelling/fixtures/suspended_floor_001431_before.pdf differ
diff --git a/tests/domain/modelling/test_elmhurst_cascade_pins.py b/tests/domain/modelling/test_elmhurst_cascade_pins.py
index bc2d6f32..16202022 100644
--- a/tests/domain/modelling/test_elmhurst_cascade_pins.py
+++ b/tests/domain/modelling/test_elmhurst_cascade_pins.py
@@ -20,6 +20,7 @@ from datatypes.epc.domain.epc_property_data import EpcPropertyData
 from domain.modelling.package_scorer import PackageScorer, Score
 from domain.modelling.product import Product
 from domain.modelling.recommendation import Recommendation
+from domain.modelling.floor_recommendation import recommend_floor_insulation
 from domain.modelling.roof_recommendation import recommend_loft_insulation
 from domain.modelling.simulation import EpcSimulation
 from domain.modelling.wall_recommendation import recommend_cavity_wall
@@ -99,3 +100,41 @@ def test_loft_overlay_reproduces_the_relodged_after() -> None:
     _assert_overlay_reproduces_after(
         before, after, recommendation.options[0].overlay
     )
+
+
+def test_solid_floor_overlay_reproduces_the_relodged_after() -> None:
+    # Arrange
+    before: EpcPropertyData = parse_recommendation_summary(
+        "solid_floor_001431_before.pdf"
+    )
+    after: EpcPropertyData = parse_recommendation_summary(
+        "solid_floor_001431_after.pdf"
+    )
+    recommendation: Recommendation | None = recommend_floor_insulation(
+        before, _AnyProduct()
+    )
+    assert recommendation is not None
+
+    # Act / Assert
+    _assert_overlay_reproduces_after(
+        before, after, recommendation.options[0].overlay
+    )
+
+
+def test_suspended_floor_overlay_reproduces_the_relodged_after() -> None:
+    # Arrange
+    before: EpcPropertyData = parse_recommendation_summary(
+        "suspended_floor_001431_before.pdf"
+    )
+    after: EpcPropertyData = parse_recommendation_summary(
+        "suspended_floor_001431_after.pdf"
+    )
+    recommendation: Recommendation | None = recommend_floor_insulation(
+        before, _AnyProduct()
+    )
+    assert recommendation is not None
+
+    # Act / Assert
+    _assert_overlay_reproduces_after(
+        before, after, recommendation.options[0].overlay
+    )