diff --git a/city_model_structure/surface.py b/city_model_structure/surface.py
index d3e8cbf8..522ad438 100644
--- a/city_model_structure/surface.py
+++ b/city_model_structure/surface.py
@@ -126,6 +126,7 @@ class Surface:
       self._inclination = np.arccos(self.normal[2])
     return self._inclination
 
+  # todo: share wall
   @property
   def type(self):
     if self._type is None:
diff --git a/city_model_structure/thermal_zone.py b/city_model_structure/thermal_zone.py
index 4f9533db..2d33ad02 100644
--- a/city_model_structure/thermal_zone.py
+++ b/city_model_structure/thermal_zone.py
@@ -14,6 +14,7 @@ class ThermalZone:
     self._indirectly_heated_area_ratio = None
     self._infiltration_rate_system_on = None
     self._infiltration_rate_system_off = None
+    self._usage_zones = None
 
   @property
   def heated(self):
@@ -84,3 +85,11 @@ class ThermalZone:
   def infiltration_rate_system_off(self, value):
     self._infiltration_rate_system_off = value
 
+  # todo: is it well defined?
+  def set_usage_zones(self, usage_zones_list):
+    if self._usage_zones is None:
+      self._usage_zones = []
+      for usage_zone in usage_zones_list:
+        self._usage_zones.append((usage_zone.percentage, usage_zone.type))
+    return self._usage_zones
+