diff --git a/tests/domain/epc/test_main_heating_system_overlay.py b/tests/domain/epc/test_main_heating_system_overlay.py
index ad6944255..c477bcee2 100644
--- a/tests/domain/epc/test_main_heating_system_overlay.py
+++ b/tests/domain/epc/test_main_heating_system_overlay.py
@@ -150,6 +150,37 @@ def test_electric_underfloor_decodes_to_its_own_code_dragging_electricity(
     assert simulation.heating.main_fuel_type == 29
 
 
+@pytest.mark.parametrize(
+    "main_heating_value",
+    [
+        # "off-peak only" / "off peak" positively claim off-peak.
+        "Electric underfloor, in concrete slab (off-peak)",
+        "Electric underfloor, integrated storage and direct-acting",
+    ],
+)
+def test_off_peak_underfloor_asserts_a_dual_meter(main_heating_value: str) -> None:
+    # Act
+    simulation = main_heating_overlay_for(main_heating_value, 0)
+
+    # Assert — an off-peak underfloor must not bill overnight heat at the peak rate.
+    assert simulation is not None
+    assert simulation.heating is not None
+    assert simulation.heating.meter_type == "Dual"
+
+
+def test_screed_underfloor_defers_the_meter_to_the_cert() -> None:
+    # "In screed above insulation (standard or off peak)" is tariff-ambiguous (81%
+    # of the corpus lodge off-peak), so the archetype cannot know the meter — it
+    # leaves meter_type unset so the cert's lodged meter stands (ADR-0046).
+    simulation = main_heating_overlay_for(
+        "Electric underfloor, in screed above insulation", 0
+    )
+
+    assert simulation is not None
+    assert simulation.heating is not None
+    assert simulation.heating.meter_type is None
+
+
 @pytest.mark.parametrize(
     ("main_heating_value", "code"),
     [