diff --git a/city_model_structure/attributes/domestic_hot_water.py b/city_model_structure/attributes/domestic_hot_water.py
deleted file mode 100644
index ab8f8cca..00000000
--- a/city_model_structure/attributes/domestic_hot_water.py
+++ /dev/null
@@ -1,53 +0,0 @@
-"""
-Building module
-SPDX - License - Identifier: LGPL - 3.0 - or -later
-Copyright © 2020 Project Author Sanam Dabirian sanam.dabirian@mail.concordia.ca
-"""
-from city_model_structure.attributes.facility import Facility
-
-
-class DomesticHotWater(Facility):
-  """
-  Domestic Hot Water facilities class
-  """
-
-  def __init__(self, number_of_baths, number_of_showers, number_of_basin, water_storage_volume, operation_schedules,
-               convective_fraction, latent_fraction, radiant_fraction, total_value_of_heat_dissipation):
-    super().__init__(operation_schedules, convective_fraction, latent_fraction, radiant_fraction,
-                     total_value_of_heat_dissipation)
-    self._number_of_baths = number_of_baths
-    self._number_of_showers = number_of_showers
-    self._number_of_basin = number_of_basin
-    self._water_storage_volume = water_storage_volume
-
-  @property
-  def number_of_baths(self):
-    """
-    Get number of baths of a building unit
-    :return: number of baths
-    """
-    return self._number_of_baths
-
-  @property
-  def number_of_showers(self):
-      """
-      Get number of showers of a building unit
-      :return: number of showers
-      """
-      return self._number_of_showers
-
-  @property
-  def number_of_basin(self):
-      """
-      Get number of wash basins of a building unit
-      :return: number of wash basins
-      """
-      return self._number_of_basin
-
-  @property
-  def water_storage_volume(self):
-      """
-      Get the volume of water storage
-      :return: volume of water storage
-      """
-      return self._water_storage_volume
diff --git a/city_model_structure/attributes/electric_appliances.py b/city_model_structure/attributes/electric_appliances.py
deleted file mode 100644
index 0c60986c..00000000
--- a/city_model_structure/attributes/electric_appliances.py
+++ /dev/null
@@ -1,26 +0,0 @@
-"""
-Building module
-SPDX - License - Identifier: LGPL - 3.0 - or -later
-Copyright © 2020 Project Author Sanam Dabirian sanam.dabirian@mail.concordia.ca
-"""
-from city_model_structure.attributes.facility import Facility
-
-
-class ElectricAppliances(Facility):
-  """
-  Electric appliance facilities class
-  """
-
-  def __init__(self, appliance_electric_power, operation_schedules, convective_fraction, latent_fraction,
-               radiant_fraction, total_value_of_heat_dissipation):
-    super().__init__(operation_schedules, convective_fraction, latent_fraction, radiant_fraction,
-                     total_value_of_heat_dissipation)
-    self._appliance_electric_power = appliance_electric_power
-
-  @property
-  def appliance_electric_power(self):
-     """
-     Get appliances electric power
-     :return: appliances electric power
-     """
-     return self._appliance_electric_power
diff --git a/city_model_structure/attributes/facility.py b/city_model_structure/attributes/facility.py
deleted file mode 100644
index 186d8dfe..00000000
--- a/city_model_structure/attributes/facility.py
+++ /dev/null
@@ -1,59 +0,0 @@
-"""
-Building module
-SPDX - License - Identifier: LGPL - 3.0 - or -later
-Copyright © 2020 Project Author Sanam Dabirian sanam.dabirian@mail.concordia.ca
-"""
-
-
-class Facility:
-  """
-  facilities class
-  """
-
-  def __init__(self, operation_schedules, convective_fraction, latent_fraction,
-               radiant_fraction, total_value_of_heat_dissipation):
-    self._operation_schedules = operation_schedules
-    self._convective_fraction = convective_fraction
-    self._latent_fraction = latent_fraction
-    self._radiant_fraction = radiant_fraction
-    self._total_value_of_heat_dissipation = total_value_of_heat_dissipation
-
-  @property
-  def operation_schedules(self):
-    """
-    Get operation schedules of the facilities
-    :return: operation schedules
-    """
-    return self._operation_schedules
-
-  @property
-  def convective_fraction(self):
-      """
-      Get convective fraction value
-      :return: convective fraction
-      """
-      return self._convective_fraction
-
-  @property
-  def latent_fraction(self):
-      """
-      Get latent fraction value
-      :return: latent fraction
-      """
-      return self._latent_fraction
-
-  @property
-  def radiant_fraction(self):
-      """
-      Get radiant fraction value
-      :return: radiant fraction
-      """
-      return self._radiant_fraction
-
-  @property
-  def total_value_of_heat_dissipation(self):
-      """
-      Get heat dissipation value
-      :return: heat dissipation
-      """
-      return self._total_value_of_heat_dissipation
diff --git a/city_model_structure/attributes/household.py b/city_model_structure/attributes/household.py
deleted file mode 100644
index ef1fe3e2..00000000
--- a/city_model_structure/attributes/household.py
+++ /dev/null
@@ -1,31 +0,0 @@
-"""
-Building module
-SPDX - License - Identifier: LGPL - 3.0 - or -later
-Copyright © 2020 Project Author Sanam Dabirian sanam.dabirian@mail.concordia.ca
-"""
-
-
-class Household:
-  """
-  Household class
-  """
-
-  def __init__(self, resident_type, household_type):
-    self._resident_type = resident_type
-    self._household_type = household_type
-
-  @property
-  def resident_type(self):
-     """
-     Get resident type
-     :return: resident type
-     """
-     return self._resident_type
-
-  @property
-  def household_type(self):
-     """
-     Get household type
-     :return: household type
-     """
-     return self._household_type
\ No newline at end of file
diff --git a/city_model_structure/attributes/hvac.py b/city_model_structure/attributes/hvac.py
deleted file mode 100644
index ea9dce9f..00000000
--- a/city_model_structure/attributes/hvac.py
+++ /dev/null
@@ -1,36 +0,0 @@
-"""
-Building module
-SPDX - License - Identifier: LGPL - 3.0 - or -later
-Copyright © 2020 Project Author Sanam Dabirian sanam.dabirian@mail.concordia.ca
-"""
-from city_model_structure.attributes.facility import Facility
-
-
-class Hvac(Facility):
-  """
-  HVAC facilities class
-  """
-
-  def __init__(self, temperature_setpoints, hvac_schedules, operation_schedules, convective_fraction, latent_fraction,
-               radiant_fraction, total_value_of_heat_dissipation):
-    super().__init__(operation_schedules, convective_fraction, latent_fraction, radiant_fraction,
-                     total_value_of_heat_dissipation)
-    self._temperature_setpoints = temperature_setpoints
-    self._hvac_schedules = hvac_schedules
-
-  @property
-  def temperature_setpoints(self):
-    """
-    Get temperature setpoints
-    :return: temperature setpoints
-    """
-    return self._temperature_setpoints
-
-  @property
-  def hvac_schedules(self):
-      """
-      Get HVAC schedules
-      :return: HVAC schedules
-      """
-      return self._hvac_schedules
-
diff --git a/city_model_structure/attributes/lighting.py b/city_model_structure/attributes/lighting.py
deleted file mode 100644
index 2913edb8..00000000
--- a/city_model_structure/attributes/lighting.py
+++ /dev/null
@@ -1,30 +0,0 @@
-"""
-Building module
-SPDX - License - Identifier: LGPL - 3.0 - or -later
-Copyright © 2020 Project Author Sanam Dabirian sanam.dabirian@mail.concordia.ca
-"""
-from city_model_structure.attributes.facility import Facility
-
-
-class Lighting(Facility):
-  """
-  Lighting facilities class
-  """
-
-  def __init__(self, electric_power, operation_schedules, convective_fraction, latent_fraction, radiant_fraction,
-               total_value_of_heat_dissipation):
-    super().__init__(operation_schedules, convective_fraction, latent_fraction, radiant_fraction,
-                     total_value_of_heat_dissipation)
-    """
-    Constructor
-    """
-
-    self._electric_power = electric_power
-
-  @property
-  def electric_power(self):
-     """
-     Get lighting electric power
-     :return: lighting electric power
-     """
-     return self._electric_power
diff --git a/city_model_structure/attributes/occupants.py b/city_model_structure/attributes/occupants.py
index a27f8ae2..bdc7263e 100644
--- a/city_model_structure/attributes/occupants.py
+++ b/city_model_structure/attributes/occupants.py
@@ -5,8 +5,10 @@ Copyright © 2020 Project Author Sanam Dabirian sanam.dabirian@mail.concordia.ca
 Contributors Pilar Monsalvete Álvarez de Uribarri pilar.monsalvete@concordia.ca
 """
 
+from typing import TypeVar
 import calendar as cal
-from city_model_structure.attributes.usage_zone import UsageZone
+
+UsageZone = TypeVar('UsageZone')
 
 
 class Occupants:
@@ -19,11 +21,10 @@ class Occupants:
     Constructor
     """
 
-    self._internal_heat_gain = None
     self._heat_dissipation = None
     self._occupancy_rate = None
     self._occupant_type = None
-    self._occupant_zone = None
+    self._usage_zone = None
     self._occupant_schedule = None
     self._number_of_occupants = None
     self._arrival_time = None
@@ -33,23 +34,6 @@ class Occupants:
     self._pd_of_meetings_duration = None
     self._complete_year_schedule = None
 
-  @property
-  def internal_heat_gain(self):
-    """
-    Get internal heat gain of occupants in W/person
-    :return: float
-    """
-    return self._internal_heat_gain
-
-  @internal_heat_gain.setter
-  def internal_heat_gain(self, value):
-    """
-    Set internal heat gain of occupants in W/person
-    :param value: float
-    :return:
-    """
-    self._internal_heat_gain = value
-
   @property
   def heat_dissipation(self):
     """
@@ -102,12 +86,12 @@ class Occupants:
     self._occupant_type = value
 
   @property
-  def occupant_zone(self) -> UsageZone:
+  def usage_zone(self) -> UsageZone:
     """
     Get the zone an occupant is in
     :return: UsageZone
     """
-    return self._occupant_zone
+    return self._usage_zone
 
   @property
   def occupant_schedule(self):
diff --git a/city_model_structure/attributes/thermal_boundary.py b/city_model_structure/attributes/thermal_boundary.py
index e505b541..3f8e280d 100644
--- a/city_model_structure/attributes/thermal_boundary.py
+++ b/city_model_structure/attributes/thermal_boundary.py
@@ -10,6 +10,7 @@ from city_model_structure.attributes.thermal_opening import ThermalOpening
 from city_model_structure.attributes.surface import Surface
 
 ThermalZone = TypeVar('ThermalZone')
+Polygon = TypeVar('Polygon')
 
 
 class ThermalBoundary:
@@ -32,13 +33,7 @@ class ThermalBoundary:
     self._he = None
     self._window_ratio = None
     self._refurbishment_measure = None
-
-    # todo: to discuss with @Guille: 1. emissivity is a function of absorptance
-    #                                2. pg 17: fraction and surface -> NO
-    self._emissivity = None
-
-    # todo: @Guille
-    self._polygon = None
+    self._surface_geometry = None
 
   @property
   def surface(self) -> Surface:
@@ -302,3 +297,11 @@ class ThermalBoundary:
     :return:
     """
     self._he = value
+
+  @property
+  def surface_geometry(self) -> Polygon:
+    """
+    Get the polygon that defines the thermal boundary
+    :return: Polygon
+    """
+    return self._surface_geometry
diff --git a/city_model_structure/attributes/thermal_opening.py b/city_model_structure/attributes/thermal_opening.py
index 23eabde6..05c6732f 100644
--- a/city_model_structure/attributes/thermal_opening.py
+++ b/city_model_structure/attributes/thermal_opening.py
@@ -4,6 +4,9 @@ SPDX - License - Identifier: LGPL - 3.0 - or -later
 Copyright © 2020 Project Author Guille Gutierrez guillermo.gutierrezmorote@concordia.ca
 Contributors Pilar Monsalvete Álvarez de Uribarri pilar.monsalvete@concordia.ca
 """
+from typing import TypeVar
+
+Polygon = TypeVar('Polygon')
 
 
 class ThermalOpening:
@@ -22,9 +25,7 @@ class ThermalOpening:
     self._overall_u_value = None
     self._hi = None
     self._he = None
-
-    # todo: discuss with @Guille
-    self._polygon = None
+    self._surface_geometry = None
 
   @property
   def area(self):
@@ -217,3 +218,11 @@ class ThermalOpening:
     :return:
     """
     self._he = value
+
+  @property
+  def surface_geometry(self) -> Polygon:
+    """
+    Get the polygon that defines the thermal opening
+    :return: Polygon
+    """
+    return self._surface_geometry
diff --git a/city_model_structure/attributes/usage_zone.py b/city_model_structure/attributes/usage_zone.py
index df4ac0ba..648dd935 100644
--- a/city_model_structure/attributes/usage_zone.py
+++ b/city_model_structure/attributes/usage_zone.py
@@ -4,10 +4,12 @@ SPDX - License - Identifier: LGPL - 3.0 - or -later
 Copyright © 2020 Project Author Pilar Monsalvete pilar_monsalvete@yahoo.es
 Contributors Guille Gutierrez guillermo.gutierrezmorote@concordia.ca
 """
-from typing import List
-from city_model_structure.attributes.internal_gains import InternalGains
-from city_model_structure.attributes.lighting import Lighting
-from city_model_structure.attributes.occupants import Occupants
+from typing import List, TypeVar
+
+InternalGains = TypeVar('InternalGains')
+Lighting = TypeVar('Lighting')
+Occupants = TypeVar('Occupants')
+Polyhedron = TypeVar('Polyhedron')
 
 
 class UsageZone:
@@ -31,6 +33,8 @@ class UsageZone:
     self._lights = None
     self._heating_schedule = None
     self._cooling_schedule = None
+    self._ventilation_schedule = None
+    self._volume_geometry = None
 
   @property
   def lights(self) -> List[Lighting]:
@@ -175,24 +179,24 @@ class UsageZone:
   @property
   def occupants(self) -> [Occupants]:
     """
-    Get occupancy data
-    :return: [Occupancy]
+    Get occupants data
+    :return: [Occupants]
     """
     return self._occupants
 
   @occupants.setter
   def occupants(self, values):
     """
-    Set occupancy
-    :param values: [Occupancy]
+    Set occupants data
+    :param values: [Occupants]
     """
     self._occupants = values
 
   @property
   def heating_schedule(self):
     """
-    Get heating schedule: list of 0, 1 that define whether the heating system is OFF or ON
-    :return: dict{DtaFrame(int)}
+    Get heating schedule: list of 0, 1 that define whether the heating system should be OFF or ON
+    :return: dict{DataFrame(int)}
     """
     return self._heating_schedule
 
@@ -200,15 +204,15 @@ class UsageZone:
   def heating_schedule(self, values):
     """
     heating schedule
-    :param values: dict{DtaFrame(int)}
+    :param values: dict{DataFrame(int)}
     """
     self._heating_schedule = values
 
   @property
   def cooling_schedule(self):
     """
-    Get cooling schedule: list of 0, 1 that define whether the heating system is OFF or ON
-    :return: dict{DtaFrame(int)}
+    Get cooling schedule: list of 0, 1 that define whether the cooling system should be OFF or ON
+    :return: dict{DataFrame(int)}
     """
     return self._cooling_schedule
 
@@ -216,10 +220,26 @@ class UsageZone:
   def cooling_schedule(self, values):
     """
     cooling schedule
-    :param values: dict{DtaFrame(int)}
+    :param values: dict{DataFrame(int)}
     """
     self._cooling_schedule = values
 
+  @property
+  def ventilation_schedule(self):
+    """
+    Get ventilation schedule: list of 0, 1 that define whether the ventilation system should be OFF or ON
+    :return: dict{DataFrame(int)}
+    """
+    return self._ventilation_schedule
+
+  @ventilation_schedule.setter
+  def ventilation_schedule(self, values):
+    """
+    ventilation_schedule schedule
+    :param values: dict{DataFrame(int)}
+    """
+    self._ventilation_schedule = values
+
   @property
   def occupancy_density(self):
     """
@@ -283,3 +303,11 @@ class UsageZone:
     :param values: float
     """
     self._electrical_app_average_consumption_sqm_year = values
+
+  @property
+  def volume_geometry(self) -> Polyhedron:
+    """
+    Get the polyhedron defined by the thermal zone
+    :return: Polyhedron
+    """
+    return self._volume_geometry