diff --git a/city_model_structure/fuel.py b/city_model_structure/fuel.py
index 6c7f4468..431f5596 100644
--- a/city_model_structure/fuel.py
+++ b/city_model_structure/fuel.py
@@ -15,6 +15,7 @@ class Fuel:
   def id(self) -> int:
     """
     Get fuel id
+    :return: int
     """
     return self._fuel_id
 
@@ -22,6 +23,7 @@ class Fuel:
   def name(self) -> str:
     """
     Get fuel name
+    :return: str
     """
     return self._name
 
@@ -29,6 +31,7 @@ class Fuel:
   def carbon_emission_factor(self) -> float:
     """
     Get fuel carbon emission factor
+    :return: float
     """
     return self._carbon_emission_factor
 
@@ -36,6 +39,7 @@ class Fuel:
   def unit(self) -> str:
     """
     Get fuel units
+    :return: str
     """
     return self._unit
 
diff --git a/city_model_structure/machine.py b/city_model_structure/machine.py
index 86857125..7c347660 100644
--- a/city_model_structure/machine.py
+++ b/city_model_structure/machine.py
@@ -24,6 +24,7 @@ class Machine:
   def id(self) -> int:
     """
     Get machine id
+    :return: int
     """
     return self._machine_id
 
@@ -31,6 +32,7 @@ class Machine:
   def name(self) -> str:
     """
     Get machine name
+    :return: str
     """
     return self._name
 
@@ -38,6 +40,7 @@ class Machine:
   def work_efficiency(self) -> float:
     """
     Get machine work efficiency
+    :return: float
     """
     return self._work_efficiency
 
@@ -45,6 +48,7 @@ class Machine:
   def work_efficiency_unit(self) -> str:
     """
     Get machine work efficiency unit
+    :return: str
     """
     return self._work_efficiency_unit
 
@@ -52,6 +56,7 @@ class Machine:
   def energy_consumption_rate(self) -> float:
     """
     Get energy consumption rate
+    :return: float
     """
     return self._energy_consumption_rate
 
@@ -59,6 +64,7 @@ class Machine:
   def energy_consumption_unit(self) -> str:
     """
     Get energy consumption unit
+    :return: str
     """
     return self._energy_consumption_unit
 
@@ -66,6 +72,7 @@ class Machine:
   def carbon_emission_factor(self) -> float:
     """
     Get carbon emission factor
+    :return: float
     """
     return self._carbon_emission_factor
 
@@ -73,6 +80,7 @@ class Machine:
   def carbon_emission_unit(self) -> str:
     """
     Get carbon emission unit
+    :return: str
     """
     return self._carbon_emission_unit
 
diff --git a/city_model_structure/material.py b/city_model_structure/material.py
index fa2f4f29..5523cf14 100644
--- a/city_model_structure/material.py
+++ b/city_model_structure/material.py
@@ -29,6 +29,7 @@ class Material:
   def material_name(self) -> str:
     """
     Get material name
+    :return: str
     """
     return self._material_name
 
@@ -36,6 +37,7 @@ class Material:
   def id(self) -> int:
     """
     Get material id
+    :return: int
     """
     return self._material_id
 
@@ -43,6 +45,7 @@ class Material:
   def type(self) -> str:
     """
     Get material type
+    :return: str
     """
     return self._type
 
@@ -50,6 +53,7 @@ class Material:
   def density(self) -> float:
     """
     Get material density
+    :return: float
     """
     return self._density
 
@@ -57,6 +61,7 @@ class Material:
   def density_unit(self) -> str:
     """
     Get material density unit
+    :return: str
     """
     return self._density_unit
 
@@ -64,6 +69,7 @@ class Material:
   def embodied_carbon(self) -> float:
     """
     Get material embodied carbon
+    :return: float
     """
     return self._embodied_carbon
 
@@ -71,6 +77,7 @@ class Material:
   def embodied_carbon_unit(self) -> str:
     """
     Get material embodied carbon unit
+    :return: str
     """
     return self._embodied_carbon_unit
 
@@ -78,6 +85,7 @@ class Material:
   def recycling_ratio(self) -> float:
     """
     Get material recycling ratio
+    :return: float
     """
     return self._recycling_ratio
 
@@ -85,6 +93,7 @@ class Material:
   def onsite_recycling_ratio(self) -> float:
     """
     Get material onsite recycling ratio
+    :return: float
     """
     return self._onsite_recycling_ratio
 
@@ -92,6 +101,7 @@ class Material:
   def company_recycling_ratio(self) -> float:
     """
     Get material company recycling ratio
+    :return: float
     """
     return self._company_recycling_ratio
 
@@ -99,6 +109,7 @@ class Material:
   def landfilling_ratio(self) -> float:
     """
     Get material landfilling ratio
+    :return: float
     """
     return self._landfilling_ratio
 
@@ -106,6 +117,7 @@ class Material:
   def cost(self) -> float:
     """
     Get material cost
+    :return: float
     """
     return self._cost
 
@@ -113,6 +125,7 @@ class Material:
   def cost_unit(self) -> str:
     """
     Get material cost unit
+    :return: str
     """
     return self._cost_unit
 
diff --git a/city_model_structure/vehicle.py b/city_model_structure/vehicle.py
index ec4b1b31..2550c812 100644
--- a/city_model_structure/vehicle.py
+++ b/city_model_structure/vehicle.py
@@ -21,6 +21,7 @@ class Vehicle:
   def id(self) -> int:
     """
     Get vehicle id
+    :return: int
     """
     return self._vehicle_id
 
@@ -28,6 +29,7 @@ class Vehicle:
   def name(self) -> str:
     """
     Get vehicle name
+    :return: str
     """
     return self._name
 
@@ -35,6 +37,7 @@ class Vehicle:
   def fuel_consumption_rate(self) -> float:
     """
     Get vehicle fuel consumption rate
+    :return: float
     """
     return self._fuel_consumption_rate
 
@@ -42,6 +45,7 @@ class Vehicle:
   def fuel_consumption_unit(self) -> str:
     """
     Get fuel consumption unit
+    :return: str
     """
     return self._fuel_consumption_unit
 
@@ -49,6 +53,7 @@ class Vehicle:
   def carbon_emission_factor(self) -> float:
     """
     Get vehicle carbon emission factor
+    :return: float
     """
     return self._carbon_emission_factor
 
@@ -56,6 +61,7 @@ class Vehicle:
   def carbon_emission_unit(self) -> str:
     """
     Get carbon emission units
+    :return: str
     """
     return self._carbon_emission_unit