diff --git a/datatypes/epc/domain/__init__.py b/datatypes/epc/domain/__init__.py
new file mode 100644
index 00000000..6ef7a4c0
--- /dev/null
+++ b/datatypes/epc/domain/__init__.py
@@ -0,0 +1,31 @@
+from .dwelling import (
+    Dwelling,
+    FloorDimensions,
+    FloorDetails,
+    HotWaterSystem,
+    LightingDetails,
+    MainHeatingSystem,
+    PropertyDetails,
+    RenewablesDetails,
+    RoofDetails,
+    SecondaryHeatingSystem,
+    VentilationDetails,
+    WallDetails,
+    WindowDetails,
+)
+
+__all__ = [
+    "Dwelling",
+    "FloorDimensions",
+    "FloorDetails",
+    "HotWaterSystem",
+    "LightingDetails",
+    "MainHeatingSystem",
+    "PropertyDetails",
+    "RenewablesDetails",
+    "RoofDetails",
+    "SecondaryHeatingSystem",
+    "VentilationDetails",
+    "WallDetails",
+    "WindowDetails",
+]
diff --git a/datatypes/epc/domain/dwelling.py b/datatypes/epc/domain/dwelling.py
new file mode 100644
index 00000000..b60cec35
--- /dev/null
+++ b/datatypes/epc/domain/dwelling.py
@@ -0,0 +1,142 @@
+from dataclasses import dataclass, field
+from typing import List, Optional
+
+
+@dataclass
+class PropertyDetails:
+    property_type: str          # e.g. "House", "Flat"
+    built_form: str             # e.g. "Mid-terrace", "Detached"
+    tenure: str                 # e.g. "Owner-occupied", "Rented Social"
+    number_of_storeys: int
+    construction_age_band: Optional[str] = None  # e.g. "1950-1966", "I: 1996 - 2002"
+    transaction_type: Optional[str] = None
+    terrain_type: Optional[str] = None
+    mains_gas_available: Optional[bool] = None
+    electricity_smart_meter: Optional[bool] = None
+    gas_smart_meter: Optional[bool] = None
+
+
+@dataclass
+class FloorDimensions:
+    """Floor area and geometry for one storey of one building part."""
+    total_floor_area_m2: float
+    height_m: float
+    heat_loss_perimeter_m: Optional[float] = None
+    party_wall_length_m: Optional[float] = None
+
+
+@dataclass
+class WallDetails:
+    construction_type: str      # e.g. "Cavity", "Solid masonry"
+    insulation_type: str        # e.g. "As built", "Filled cavity", "External"
+    thickness_mm: Optional[int] = None
+    party_wall_construction_type: Optional[str] = None
+
+
+@dataclass
+class RoofDetails:
+    construction_type: str      # e.g. "Pitched, access to loft", "Flat"
+    insulation_at: Optional[str] = None         # e.g. "Joists", "Rafters"
+    insulation_thickness_mm: Optional[int] = None
+    has_rooms_in_roof: bool = False
+
+
+@dataclass
+class FloorDetails:
+    construction_type: str      # e.g. "Solid", "Suspended timber"
+    insulation_type: Optional[str] = None       # e.g. "As built", "Insulated"
+
+
+@dataclass
+class WindowDetails:
+    glazing_type: str           # e.g. "Double glazing", "Triple glazing"
+    orientation: Optional[str] = None
+    frame_type: Optional[str] = None
+    glazing_gap: Optional[str] = None
+    draught_proofed: Optional[bool] = None
+    height_m: Optional[float] = None
+    width_m: Optional[float] = None
+
+
+@dataclass
+class MainHeatingSystem:
+    fuel: str                   # e.g. "Mains gas", "Oil", "Electricity"
+    system_type: str            # e.g. "Boiler with radiators or underfloor heating"
+    boiler_type: Optional[str] = None           # e.g. "Regular", "Combi"
+    manufacturer: Optional[str] = None
+    model: Optional[str] = None
+    condensing: Optional[bool] = None
+    controls: Optional[str] = None
+    flue_gas_heat_recovery: bool = False
+    weather_compensator: bool = False
+    emitter: Optional[str] = None              # e.g. "Radiators", "Underfloor"
+
+
+@dataclass
+class HotWaterSystem:
+    source: str                 # e.g. "From main heating 1", "Immersion heater"
+    cylinder_size: Optional[str] = None
+    insulation_type: Optional[str] = None
+    insulation_thickness_mm: Optional[int] = None
+    has_thermostat: Optional[bool] = None
+
+
+@dataclass
+class SecondaryHeatingSystem:
+    fuel: str                   # e.g. "Wood logs", "Electricity"
+
+
+@dataclass
+class VentilationDetails:
+    ventilation_type: str       # e.g. "Natural", "Mechanical Extract - Decentralised"
+    number_of_open_flues: int = 0
+    number_of_closed_flues: int = 0
+    number_of_boiler_flues: int = 0
+    number_of_other_flues: int = 0
+    number_of_extract_fans: int = 0
+    number_of_passive_vents: int = 0
+    number_of_flueless_gas_fires: int = 0
+    has_fixed_air_conditioning: bool = False
+    pressure_test: Optional[str] = None
+    draught_lobby: Optional[bool] = None
+
+
+@dataclass
+class RenewablesDetails:
+    has_photovoltaic: bool = False
+    has_solar_hot_water: bool = False
+    has_wind_turbines: bool = False
+    has_hydro: bool = False
+    number_of_pv_batteries: int = 0
+
+
+@dataclass
+class LightingDetails:
+    number_of_led_bulbs: Optional[int] = None
+    number_of_cfl_bulbs: Optional[int] = None
+    number_of_incandescent_bulbs: Optional[int] = None
+
+
+@dataclass
+class Dwelling:
+    property_details: PropertyDetails
+    # One entry per storey per building part (main building + any extensions, flattened)
+    floor_dimensions: List[FloorDimensions]
+    walls: WallDetails
+    roof: RoofDetails
+    floor: FloorDetails
+    windows: List[WindowDetails]
+    main_heating: MainHeatingSystem
+    hot_water: HotWaterSystem
+    ventilation: VentilationDetails
+    renewables: RenewablesDetails
+    lighting: LightingDetails
+    number_of_habitable_rooms: int
+    number_of_external_doors: int
+    number_of_open_chimneys: int
+    has_conservatory: bool = False
+    secondary_heating: Optional[SecondaryHeatingSystem] = None
+    number_of_blocked_chimneys: int = 0
+    number_of_baths: Optional[int] = None
+    number_of_showers: Optional[int] = None
+    waste_water_heat_recovery: Optional[str] = None
diff --git a/datatypes/epc/domain/mapper.py b/datatypes/epc/domain/mapper.py
new file mode 100644
index 00000000..3f3fa003
--- /dev/null
+++ b/datatypes/epc/domain/mapper.py
@@ -0,0 +1,9 @@
+from datatypes.epc.domain.dwelling import Dwelling
+from datatypes.epc.surveys.pashub_rdsap_site_notes import PasHubRdSapSiteNotes
+
+
+class DwellingMapper:
+
+    @staticmethod
+    def from_site_notes(survey: PasHubRdSapSiteNotes) -> Dwelling:
+        raise NotImplementedError
diff --git a/datatypes/epc/domain/tests/__init__.py b/datatypes/epc/domain/tests/__init__.py
new file mode 100644
index 00000000..e69de29b
diff --git a/datatypes/epc/domain/tests/test_from_site_notes.py b/datatypes/epc/domain/tests/test_from_site_notes.py
new file mode 100644
index 00000000..3714dc22
--- /dev/null
+++ b/datatypes/epc/domain/tests/test_from_site_notes.py
@@ -0,0 +1,350 @@
+import json
+import os
+from typing import Any, Dict
+
+import pytest
+
+from datatypes.epc.domain import Dwelling
+from datatypes.epc.domain.mapper import DwellingMapper
+from datatypes.epc.schema.tests.helpers import from_dict
+from datatypes.epc.surveys.pashub_rdsap_site_notes import PasHubRdSapSiteNotes
+
+FIXTURES = os.path.join(
+    os.path.dirname(__file__),
+    "../../surveys/tests/fixtures",
+)
+
+
+def load(filename: str) -> Dict[str, Any]:
+    with open(os.path.join(FIXTURES, filename)) as f:
+        return json.load(f)  # type: ignore[no-any-return]
+
+
+def survey(filename: str) -> PasHubRdSapSiteNotes:
+    return from_dict(PasHubRdSapSiteNotes, load(filename))
+
+
+class TestFromExample1:
+    """No extensions; regular boiler with cylinder; natural ventilation."""
+
+    @pytest.fixture
+    def dwelling(self) -> Dwelling:
+        return DwellingMapper.from_site_notes(survey("example1.json"))
+
+    # --- property_details ---
+
+    def test_property_type(self, dwelling: Dwelling) -> None:
+        assert dwelling.property_details.property_type == "House"
+
+    def test_built_form(self, dwelling: Dwelling) -> None:
+        assert dwelling.property_details.built_form == "Mid-terrace"
+
+    def test_tenure(self, dwelling: Dwelling) -> None:
+        assert dwelling.property_details.tenure == "Rented Social"
+
+    def test_number_of_storeys(self, dwelling: Dwelling) -> None:
+        assert dwelling.property_details.number_of_storeys == 2
+
+    def test_construction_age_band(self, dwelling: Dwelling) -> None:
+        assert dwelling.property_details.construction_age_band == "I: 1996 - 2002"
+
+    def test_transaction_type(self, dwelling: Dwelling) -> None:
+        assert dwelling.property_details.transaction_type == "None of the Above"
+
+    def test_terrain_type(self, dwelling: Dwelling) -> None:
+        assert dwelling.property_details.terrain_type == "Suburban"
+
+    def test_mains_gas_available(self, dwelling: Dwelling) -> None:
+        assert dwelling.property_details.mains_gas_available is True
+
+    def test_electricity_smart_meter(self, dwelling: Dwelling) -> None:
+        assert dwelling.property_details.electricity_smart_meter is True
+
+    def test_gas_smart_meter(self, dwelling: Dwelling) -> None:
+        assert dwelling.property_details.gas_smart_meter is True
+
+    # --- floor_dimensions ---
+
+    def test_floor_count(self, dwelling: Dwelling) -> None:
+        # 2 floors from main building, no extensions
+        assert len(dwelling.floor_dimensions) == 2
+
+    def test_floor_area(self, dwelling: Dwelling) -> None:
+        assert dwelling.floor_dimensions[0].total_floor_area_m2 == 24.78
+
+    def test_floor_height(self, dwelling: Dwelling) -> None:
+        assert dwelling.floor_dimensions[0].height_m == 2.37
+
+    def test_heat_loss_perimeter(self, dwelling: Dwelling) -> None:
+        assert dwelling.floor_dimensions[0].heat_loss_perimeter_m == 14.21
+
+    def test_party_wall_length(self, dwelling: Dwelling) -> None:
+        assert dwelling.floor_dimensions[0].party_wall_length_m == 6.15
+
+    # --- walls ---
+
+    def test_wall_construction_type(self, dwelling: Dwelling) -> None:
+        assert dwelling.walls.construction_type == "Cavity"
+
+    def test_wall_insulation_type(self, dwelling: Dwelling) -> None:
+        assert dwelling.walls.insulation_type == "As built"
+
+    def test_wall_thickness(self, dwelling: Dwelling) -> None:
+        assert dwelling.walls.thickness_mm == 280
+
+    def test_party_wall_construction_type(self, dwelling: Dwelling) -> None:
+        assert dwelling.walls.party_wall_construction_type == "Cavity Masonry, Unfilled"
+
+    # --- roof ---
+
+    def test_roof_construction_type(self, dwelling: Dwelling) -> None:
+        assert dwelling.roof.construction_type == "Pitched roof (Slates or tiles), Access to loft"
+
+    def test_roof_insulation_at(self, dwelling: Dwelling) -> None:
+        assert dwelling.roof.insulation_at == "Joists"
+
+    def test_roof_insulation_thickness(self, dwelling: Dwelling) -> None:
+        assert dwelling.roof.insulation_thickness_mm == 100
+
+    def test_roof_no_rooms_in_roof(self, dwelling: Dwelling) -> None:
+        assert dwelling.roof.has_rooms_in_roof is False
+
+    # --- floor ---
+
+    def test_floor_construction_type(self, dwelling: Dwelling) -> None:
+        assert dwelling.floor.construction_type == "Suspended, not timber"
+
+    def test_floor_insulation_type(self, dwelling: Dwelling) -> None:
+        assert dwelling.floor.insulation_type == "As Built"
+
+    # --- windows ---
+
+    def test_window_count(self, dwelling: Dwelling) -> None:
+        assert len(dwelling.windows) == 4
+
+    def test_window_glazing_type(self, dwelling: Dwelling) -> None:
+        assert dwelling.windows[0].glazing_type == "Double glazing, Unknown install date"
+
+    def test_window_orientation(self, dwelling: Dwelling) -> None:
+        assert dwelling.windows[0].orientation == "South East"
+
+    def test_window_frame_type(self, dwelling: Dwelling) -> None:
+        assert dwelling.windows[0].frame_type == "Wooden or PVC"
+
+    def test_window_glazing_gap(self, dwelling: Dwelling) -> None:
+        assert dwelling.windows[0].glazing_gap == "16 mm or more"
+
+    def test_window_draught_proofed(self, dwelling: Dwelling) -> None:
+        assert dwelling.windows[0].draught_proofed is True
+
+    def test_window_dimensions(self, dwelling: Dwelling) -> None:
+        assert dwelling.windows[0].height_m == 1.36
+        assert dwelling.windows[0].width_m == 1.0
+
+    # --- main_heating ---
+
+    def test_main_heating_fuel(self, dwelling: Dwelling) -> None:
+        assert dwelling.main_heating.fuel == "Mains gas"
+
+    def test_main_heating_system_type(self, dwelling: Dwelling) -> None:
+        assert dwelling.main_heating.system_type == "Boiler with radiators or underfloor heating"
+
+    def test_main_heating_boiler_type(self, dwelling: Dwelling) -> None:
+        assert dwelling.main_heating.boiler_type == "Regular"
+
+    def test_main_heating_manufacturer(self, dwelling: Dwelling) -> None:
+        assert dwelling.main_heating.manufacturer == "Vaillant"
+
+    def test_main_heating_model(self, dwelling: Dwelling) -> None:
+        assert dwelling.main_heating.model == "ecoFIT sustain 415"
+
+    def test_main_heating_condensing(self, dwelling: Dwelling) -> None:
+        assert dwelling.main_heating.condensing is True
+
+    def test_main_heating_controls(self, dwelling: Dwelling) -> None:
+        assert dwelling.main_heating.controls == "Programmer, room thermostat and TRVs"
+
+    def test_main_heating_fghr(self, dwelling: Dwelling) -> None:
+        assert dwelling.main_heating.flue_gas_heat_recovery is False
+
+    def test_main_heating_weather_compensator(self, dwelling: Dwelling) -> None:
+        assert dwelling.main_heating.weather_compensator is False
+
+    def test_main_heating_emitter(self, dwelling: Dwelling) -> None:
+        assert dwelling.main_heating.emitter == "Radiators"
+
+    # --- hot_water ---
+
+    def test_hot_water_source(self, dwelling: Dwelling) -> None:
+        assert dwelling.hot_water.source == "From main heating 1"
+
+    def test_hot_water_cylinder_size(self, dwelling: Dwelling) -> None:
+        assert dwelling.hot_water.cylinder_size == "Normal (90-130 litres)"
+
+    def test_hot_water_insulation_type(self, dwelling: Dwelling) -> None:
+        assert dwelling.hot_water.insulation_type == "Factory fitted"
+
+    def test_hot_water_insulation_thickness(self, dwelling: Dwelling) -> None:
+        assert dwelling.hot_water.insulation_thickness_mm == 12
+
+    def test_hot_water_thermostat(self, dwelling: Dwelling) -> None:
+        assert dwelling.hot_water.has_thermostat is True
+
+    # --- secondary_heating ---
+
+    def test_secondary_heating_absent(self, dwelling: Dwelling) -> None:
+        # "No Secondary Heating" maps to None
+        assert dwelling.secondary_heating is None
+
+    # --- ventilation ---
+
+    def test_ventilation_type(self, dwelling: Dwelling) -> None:
+        assert dwelling.ventilation.ventilation_type == "Natural"
+
+    def test_ventilation_extract_fans(self, dwelling: Dwelling) -> None:
+        assert dwelling.ventilation.number_of_extract_fans == 2
+
+    def test_ventilation_no_air_conditioning(self, dwelling: Dwelling) -> None:
+        assert dwelling.ventilation.has_fixed_air_conditioning is False
+
+    def test_ventilation_pressure_test(self, dwelling: Dwelling) -> None:
+        assert dwelling.ventilation.pressure_test == "No test"
+
+    def test_ventilation_draught_lobby(self, dwelling: Dwelling) -> None:
+        assert dwelling.ventilation.draught_lobby is False
+
+    # --- renewables ---
+
+    def test_no_photovoltaic(self, dwelling: Dwelling) -> None:
+        assert dwelling.renewables.has_photovoltaic is False
+
+    def test_no_solar_hot_water(self, dwelling: Dwelling) -> None:
+        assert dwelling.renewables.has_solar_hot_water is False
+
+    def test_no_wind_turbines(self, dwelling: Dwelling) -> None:
+        assert dwelling.renewables.has_wind_turbines is False
+
+    def test_pv_batteries_count(self, dwelling: Dwelling) -> None:
+        assert dwelling.renewables.number_of_pv_batteries == 0
+
+    # --- lighting ---
+
+    def test_led_bulbs(self, dwelling: Dwelling) -> None:
+        assert dwelling.lighting.number_of_led_bulbs == 5
+
+    def test_cfl_bulbs(self, dwelling: Dwelling) -> None:
+        assert dwelling.lighting.number_of_cfl_bulbs == 4
+
+    def test_incandescent_bulbs(self, dwelling: Dwelling) -> None:
+        assert dwelling.lighting.number_of_incandescent_bulbs == 0
+
+    # --- dwelling-level counts ---
+
+    def test_habitable_rooms(self, dwelling: Dwelling) -> None:
+        assert dwelling.number_of_habitable_rooms == 2
+
+    def test_external_doors(self, dwelling: Dwelling) -> None:
+        assert dwelling.number_of_external_doors == 2
+
+    def test_open_chimneys(self, dwelling: Dwelling) -> None:
+        assert dwelling.number_of_open_chimneys == 0
+
+    def test_blocked_chimneys(self, dwelling: Dwelling) -> None:
+        assert dwelling.number_of_blocked_chimneys == 0
+
+    def test_no_conservatory(self, dwelling: Dwelling) -> None:
+        assert dwelling.has_conservatory is False
+
+    def test_baths(self, dwelling: Dwelling) -> None:
+        assert dwelling.number_of_baths == 1
+
+    def test_showers(self, dwelling: Dwelling) -> None:
+        assert dwelling.number_of_showers == 1
+
+    def test_waste_water_heat_recovery(self, dwelling: Dwelling) -> None:
+        assert dwelling.waste_water_heat_recovery == "None"
+
+
+class TestFromExample2:
+    """With extensions; combi boiler (no cylinder); mechanical extract ventilation."""
+
+    @pytest.fixture
+    def dwelling(self) -> Dwelling:
+        return DwellingMapper.from_site_notes(survey("example2.json"))
+
+    # --- floor_dimensions: main building + extension floors flattened ---
+
+    def test_floor_count_includes_extensions(self, dwelling: Dwelling) -> None:
+        # 2 main building floors + 1 extension floor = 3
+        assert len(dwelling.floor_dimensions) == 3
+
+    def test_extension_floor_area(self, dwelling: Dwelling) -> None:
+        # Extension floor is last; area 3.8 m²
+        assert dwelling.floor_dimensions[2].total_floor_area_m2 == 3.8
+
+    def test_extension_floor_party_wall_length(self, dwelling: Dwelling) -> None:
+        assert dwelling.floor_dimensions[2].party_wall_length_m == 0.0
+
+    # --- walls: from main building ---
+
+    def test_wall_insulation_type_filled_cavity(self, dwelling: Dwelling) -> None:
+        assert dwelling.walls.insulation_type == "Filled Cavity"
+
+    def test_wall_thickness(self, dwelling: Dwelling) -> None:
+        assert dwelling.walls.thickness_mm == 310
+
+    # --- roof: from main building ---
+
+    def test_roof_insulation_thickness(self, dwelling: Dwelling) -> None:
+        assert dwelling.roof.insulation_thickness_mm == 100
+
+    # --- windows: all 8, location info discarded ---
+
+    def test_window_count(self, dwelling: Dwelling) -> None:
+        assert len(dwelling.windows) == 8
+
+    # --- main_heating ---
+
+    def test_main_heating_boiler_type_combi(self, dwelling: Dwelling) -> None:
+        assert dwelling.main_heating.boiler_type == "Combi"
+
+    def test_main_heating_model(self, dwelling: Dwelling) -> None:
+        assert dwelling.main_heating.model == "ecoTEC pro 28"
+
+    # --- hot_water: combi has no cylinder ---
+
+    def test_hot_water_source(self, dwelling: Dwelling) -> None:
+        assert dwelling.hot_water.source == "From main heating 1"
+
+    def test_hot_water_cylinder_size_no_cylinder(self, dwelling: Dwelling) -> None:
+        assert dwelling.hot_water.cylinder_size == "No Cylinder"
+
+    def test_hot_water_insulation_type_none(self, dwelling: Dwelling) -> None:
+        assert dwelling.hot_water.insulation_type is None
+
+    def test_hot_water_thermostat_none(self, dwelling: Dwelling) -> None:
+        assert dwelling.hot_water.has_thermostat is None
+
+    # --- ventilation ---
+
+    def test_ventilation_type_mechanical(self, dwelling: Dwelling) -> None:
+        assert dwelling.ventilation.ventilation_type == "Mechanical Extract - Decentralised"
+
+    def test_ventilation_extract_fans_zero(self, dwelling: Dwelling) -> None:
+        assert dwelling.ventilation.number_of_extract_fans == 0
+
+    # --- lighting ---
+
+    def test_incandescent_bulbs(self, dwelling: Dwelling) -> None:
+        assert dwelling.lighting.number_of_incandescent_bulbs == 4
+
+    def test_led_bulbs_zero(self, dwelling: Dwelling) -> None:
+        assert dwelling.lighting.number_of_led_bulbs == 0
+
+    # --- counts ---
+
+    def test_habitable_rooms(self, dwelling: Dwelling) -> None:
+        assert dwelling.number_of_habitable_rooms == 3
+
+    def test_showers(self, dwelling: Dwelling) -> None:
+        assert dwelling.number_of_showers == 1