diff --git a/domain/building_geometry.py b/domain/building_geometry.py
index f4ba844b..b6e535fe 100644
--- a/domain/building_geometry.py
+++ b/domain/building_geometry.py
@@ -45,3 +45,18 @@ def roof_area(epc: EpcPropertyData, identifier: BuildingPartIdentifier) -> float
     return round(
         max(fd.total_floor_area_m2 for fd in part.sap_floor_dimensions), 2
     )
+
+
+def ground_floor_area(
+    epc: EpcPropertyData, identifier: BuildingPartIdentifier
+) -> float:
+    """Ground-floor area of one building part, in m^2 — the area of its lowest
+    floor (``floor == 0``), the surface a ground-floor insulation measure
+    treats."""
+    part = next(
+        candidate
+        for candidate in epc.sap_building_parts
+        if candidate.identifier is identifier
+    )
+    ground = next(fd for fd in part.sap_floor_dimensions if fd.floor == 0)
+    return round(ground.total_floor_area_m2, 2)
diff --git a/domain/modelling/contingencies.py b/domain/modelling/contingencies.py
index f40c4851..8d0230ff 100644
--- a/domain/modelling/contingencies.py
+++ b/domain/modelling/contingencies.py
@@ -8,6 +8,8 @@ extended as each measure type lands.
 _CONTINGENCY_RATES: dict[str, float] = {
     "cavity_wall_insulation": 0.10,
     "loft_insulation": 0.10,
+    "suspended_floor_insulation": 0.20,
+    "solid_floor_insulation": 0.26,
 }
 
 
diff --git a/domain/modelling/floor_recommendation.py b/domain/modelling/floor_recommendation.py
new file mode 100644
index 00000000..a6992a85
--- /dev/null
+++ b/domain/modelling/floor_recommendation.py
@@ -0,0 +1,84 @@
+"""The floor Recommendation Generator.
+
+Detects an uninsulated ground floor and its construction (suspended timber vs
+solid) and emits a Recommendation whose single Measure Option carries the
+matching insulation Simulation Overlay and a priced Cost. A floor is one
+construction, so — like a cavity wall — there is one Option, chosen by
+detection. No scoring, no persistence (ADR-0016).
+"""
+
+from typing import Optional, Union
+
+from datatypes.epc.domain.epc_property_data import (
+    BuildingPartIdentifier,
+    EpcPropertyData,
+    SapBuildingPart,
+)
+from domain.building_geometry import ground_floor_area
+from domain.modelling.recommendation import Cost, MeasureOption, Recommendation
+from domain.modelling.simulation import BuildingPartOverlay, EpcSimulation
+from repositories.product.product_repository import ProductRepository
+
+# Recommended ground-floor insulation depth (mm).
+_RECOMMENDED_FLOOR_THICKNESS_MM = 100
+
+
+def _is_uninsulated(thickness: Optional[Union[str, int]]) -> bool:
+    """A lodged floor-insulation thickness of nothing / blank / zero is an
+    uninsulated floor; any positive thickness is already insulated."""
+    if thickness is None:
+        return True
+    if isinstance(thickness, int):
+        return thickness == 0
+    return thickness.strip() in ("", "0")
+
+
+def _floor_measure_type(construction_type: Optional[str]) -> Optional[str]:
+    """Map the lodged floor construction to the insulation Measure Type, or
+    None when the construction is not a treatable suspended/solid floor."""
+    text = (construction_type or "").lower()
+    if "suspended" in text:
+        return "suspended_floor_insulation"
+    if "solid" in text:
+        return "solid_floor_insulation"
+    return None
+
+
+def recommend_floor_insulation(
+    epc: EpcPropertyData, products: ProductRepository
+) -> Optional[Recommendation]:
+    """Return a ground-floor insulation Recommendation for the main part's
+    uninsulated ground floor, else None."""
+    main: SapBuildingPart = next(
+        part
+        for part in epc.sap_building_parts
+        if part.identifier is BuildingPartIdentifier.MAIN
+    )
+
+    if not _is_uninsulated(main.floor_insulation_thickness):
+        return None
+
+    measure_type = _floor_measure_type(main.floor_construction_type)
+    if measure_type is None:
+        return None
+
+    product = products.get(measure_type)
+    area: float = ground_floor_area(epc, BuildingPartIdentifier.MAIN)
+    cost = Cost(
+        total=area * product.unit_cost_per_m2,
+        contingency_rate=product.contingency_rate,
+    )
+
+    option = MeasureOption(
+        measure_type=measure_type,
+        description="Ground-floor insulation",
+        overlay=EpcSimulation(
+            building_parts={
+                BuildingPartIdentifier.MAIN: BuildingPartOverlay(
+                    floor_insulation_thickness=_RECOMMENDED_FLOOR_THICKNESS_MM
+                )
+            }
+        ),
+        cost=cost,
+    )
+    return Recommendation(surface="Ground floor", options=(option,))
diff --git a/domain/modelling/simulation.py b/domain/modelling/simulation.py
index 9a3c7e64..5b2ba8a6 100644
--- a/domain/modelling/simulation.py
+++ b/domain/modelling/simulation.py
@@ -23,6 +23,7 @@ class BuildingPartOverlay:
 
     wall_insulation_type: Optional[int] = None
     roof_insulation_thickness: Optional[int] = None
+    floor_insulation_thickness: Optional[int] = None
 
 
 def _no_building_parts() -> dict[BuildingPartIdentifier, BuildingPartOverlay]:
diff --git a/tests/domain/modelling/test_floor_recommendation.py b/tests/domain/modelling/test_floor_recommendation.py
new file mode 100644
index 00000000..8ed2871f
--- /dev/null
+++ b/tests/domain/modelling/test_floor_recommendation.py
@@ -0,0 +1,97 @@
+"""Behaviour of the floor Recommendation Generator: detecting an uninsulated
+ground floor and its construction (suspended vs solid), emitting the matching
+single insulation Option with overlay + priced Cost. A floor is one
+construction, so this is a single-Option Recommendation (like cavity walls).
+"""
+
+from datatypes.epc.domain.epc_property_data import (
+    BuildingPartIdentifier,
+    EpcPropertyData,
+    SapBuildingPart,
+)
+from domain.modelling.overlay_applicator import apply_simulations
+from domain.modelling.product import Product
+from domain.modelling.recommendation import Recommendation
+from domain.modelling.floor_recommendation import recommend_floor_insulation
+from repositories.product.product_repository import ProductRepository
+from tests.domain.sap10_calculator.worksheet._elmhurst_worksheet_000490 import (
+    build_epc,
+)
+
+
+class _StubProducts(ProductRepository):
+    def get(self, measure_type: str) -> Product:
+        return Product(
+            measure_type=measure_type, unit_cost_per_m2=25.0, contingency_rate=0.20
+        )
+
+
+def _main(epc: EpcPropertyData) -> SapBuildingPart:
+    return next(
+        p for p in epc.sap_building_parts if p.identifier is BuildingPartIdentifier.MAIN
+    )
+
+
+def test_uninsulated_suspended_floor_yields_suspended_insulation() -> None:
+    # Arrange — 000490 MAIN: "Suspended timber", "As built" (uninsulated)
+    baseline: EpcPropertyData = build_epc()
+
+    # Act
+    recommendation: Recommendation | None = recommend_floor_insulation(
+        baseline, _StubProducts()
+    )
+
+    # Assert
+    assert recommendation is not None
+    assert recommendation.surface == "Ground floor"
+    assert len(recommendation.options) == 1
+    option = recommendation.options[0]
+    assert option.measure_type == "suspended_floor_insulation"
+    simulated: EpcPropertyData = apply_simulations(baseline, [option.overlay])
+    assert _main(simulated).floor_insulation_thickness == 100
+
+
+def test_uninsulated_solid_floor_yields_solid_insulation() -> None:
+    # Arrange
+    baseline: EpcPropertyData = build_epc()
+    _main(baseline).floor_construction_type = "Solid"
+
+    # Act
+    recommendation: Recommendation | None = recommend_floor_insulation(
+        baseline, _StubProducts()
+    )
+
+    # Assert
+    assert recommendation is not None
+    assert recommendation.options[0].measure_type == "solid_floor_insulation"
+
+
+def test_already_insulated_floor_yields_no_recommendation() -> None:
+    # Arrange
+    baseline: EpcPropertyData = build_epc()
+    _main(baseline).floor_insulation_thickness = "100"
+
+    # Act
+    recommendation: Recommendation | None = recommend_floor_insulation(
+        baseline, _StubProducts()
+    )
+
+    # Assert
+    assert recommendation is None
+
+
+def test_floor_option_carries_cost_from_ground_floor_area_and_product() -> None:
+    # Arrange — 000490 MAIN ground floor area 14.85 m^2
+    baseline: EpcPropertyData = build_epc()
+
+    # Act
+    recommendation: Recommendation | None = recommend_floor_insulation(
+        baseline, _StubProducts()
+    )
+
+    # Assert
+    assert recommendation is not None
+    cost = recommendation.options[0].cost
+    assert cost is not None
+    assert abs(cost.total - 14.85 * 25.0) <= 0.01
+    assert abs(cost.contingency_rate - 0.20) <= 1e-9
diff --git a/tests/domain/test_building_geometry.py b/tests/domain/test_building_geometry.py
index 548e6675..403d79bd 100644
--- a/tests/domain/test_building_geometry.py
+++ b/tests/domain/test_building_geometry.py
@@ -2,7 +2,11 @@
 reusable outside the SAP calculator (e.g. for Modelling cost quantities)."""
 
 from datatypes.epc.domain.epc_property_data import BuildingPartIdentifier
-from domain.building_geometry import gross_heat_loss_wall_area, roof_area
+from domain.building_geometry import (
+    gross_heat_loss_wall_area,
+    ground_floor_area,
+    roof_area,
+)
 from tests.domain.sap10_calculator.worksheet._elmhurst_worksheet_000490 import (
     build_epc,
 )
@@ -33,3 +37,14 @@ def test_roof_area_is_the_parts_greatest_floor_area() -> None:
 
     # Assert
     assert abs(area - 14.85) <= 0.01
+
+
+def test_ground_floor_area_is_the_lowest_floors_area() -> None:
+    # Arrange — 000490 MAIN floor 0 total area is 14.85 m^2
+    epc = build_epc()
+
+    # Act
+    area: float = ground_floor_area(epc, BuildingPartIdentifier.MAIN)
+
+    # Assert
+    assert abs(area - 14.85) <= 0.01