diff --git a/city_model_structure/building_demand/thermal_boundary.py b/city_model_structure/building_demand/thermal_boundary.py
index 9bbd5943..cf5ede7c 100644
--- a/city_model_structure/building_demand/thermal_boundary.py
+++ b/city_model_structure/building_demand/thermal_boundary.py
@@ -9,6 +9,7 @@ Code contributors: Pilar Monsalvete Alvarez de Uribarri pilar.monsalvete@concord
 import uuid
 from typing import List, Union, TypeVar
 from helpers.configuration_helper import ConfigurationHelper as ch
+import helpers.constants as cte
 from city_model_structure.building_demand.layer import Layer
 from city_model_structure.building_demand.thermal_opening import ThermalOpening
 from city_model_structure.building_demand.thermal_zone import ThermalZone
@@ -213,7 +214,10 @@ class ThermalBoundary:
     if self._u_value is None:
       h_i = self.hi
       h_e = self.he
-      r_value = 1.0/h_i + 1.0/h_e
+      if self.type == cte.GROUND:
+        r_value = 1.0 / h_i
+      else:
+        r_value = 1.0/h_i + 1.0/h_e
       try:
         for layer in self.layers:
           if layer.material.no_mass:
diff --git a/city_model_structure/building_demand/thermal_zone.py b/city_model_structure/building_demand/thermal_zone.py
index 417a6b39..1e66402e 100644
--- a/city_model_structure/building_demand/thermal_zone.py
+++ b/city_model_structure/building_demand/thermal_zone.py
@@ -52,26 +52,26 @@ class ThermalZone:
     self._appliances = None
     self._internal_gains = None
     self._thermal_control = None
-    self._usage_zones = None
+    self._usages = None
 
   @property
   def usage_zones(self):
     # example 70-office_30-residential
     if self._usage_from_parent:
-      self._usage_zones = copy.deepcopy(self._parent_internal_zone.usage_zones)
+      self._usages = copy.deepcopy(self._parent_internal_zone.usage_zones)
     else:
       values = self._usage.split('_')
       usages = []
       for value in values:
         usages.append(value.split('-'))
-      self._usage_zones = []
-      for parent_usage_zone in self._parent_internal_zone.usage_zones:
+      self._usages = []
+      for parent_usage in self._parent_internal_zone.usage_zones:
         for value in usages:
-          if parent_usage_zone.usage == value[1]:
-            new_usage_zone = copy.deepcopy(parent_usage_zone)
-            new_usage_zone.percentage = float(value[0])/100
-            self._usage_zones.append(new_usage_zone)
-    return self._usage_zones
+          if parent_usage.usage == value[1]:
+            new_usage = copy.deepcopy(parent_usage)
+            new_usage.percentage = float(value[0])/100
+            self._usages.append(new_usage)
+    return self._usages
 
   @property
   def id(self):
@@ -102,7 +102,7 @@ class ThermalZone:
   @property
   def additional_thermal_bridge_u_value(self) -> Union[None, float]:
     """
-    Get thermal zone additional thermal bridge u value W/m2K
+    Get thermal zone additional thermal bridge u value per footprint area W/m2K
     :return: None or float
     """
     return self._additional_thermal_bridge_u_value
@@ -110,7 +110,7 @@ class ThermalZone:
   @additional_thermal_bridge_u_value.setter
   def additional_thermal_bridge_u_value(self, value):
     """
-    Set thermal zone additional thermal bridge u value W/m2K
+    Set thermal zone additional thermal bridge u value per footprint area W/m2K
     :param value: float
     """
     if value is not None: