Creating new cost class to handle new costing data

backend/app/plan/utils.py

@@ -173,7 +173,7 @@ def create_recommendation_scoring_data(
         parts = recommendation["parts"]
         if len(parts) != 1:
             raise ValueError("More than one part for roof insulation - investiage me")
-
+        
         scoring_dict["roof_insulation_thickness_ENDING"] = str(parts[0]["depths"][0])
         scoring_dict["ROOF_ENERGY_EFF_ENDING"] = "Very Good"
     else:

recommendations/Costs.py

@@ -0,0 +1,139 @@
+class Costs:
+    """
+    A class to calculate the costs associated with construction works,
+    specifically focusing on cavity wall insulation.
+    It includes contingency, preliminaries, profit margin, and VAT calculations.
+
+    As a sense check, there is a useful article from checkatrade on retrofitting walls and expected costs:
+    https://www.checkatrade.com/blog/cost-guides/retrofit-insulation-cost/
+    """
+
+    # Contingency is a percentage of the total cost of the work and covers unforseen expenses
+    # We assume a conservative 10% contingency for all works which is a rate defined by SPONs
+    CONTINGENCY = 0.1
+
+    # Preliminaries are a percentage of the total cost of the work and covers the cost of site-specific costs
+    # such as site preparation, safety measures and project management. This rate can vary but we'll assume a 10%
+    # rate, on the total cost before VAT, as recommended by SPONs
+    PRELIMINARIES = 0.1
+
+    VAT_RATE = 0.2
+    PROFIT_MARGIN = 0.15
+
+    def __init__(self, property_instance):
+        """
+        Initializes the Costs class with a property instance.
+
+        :param property_instance: Instance of a Property class containing relevant details like wall area.
+        """
+        if not hasattr(property_instance, 'insulation_wall_area'):
+            raise ValueError("Property instance must have an 'insulation_wall_area' attribute")
+        self.property = property_instance
+
+    def cavity_wall_insulation(self, material):
+        """
+        Calculates the total cost for cavity wall insulation based on material and labor costs,
+        including contingency, preliminaries, profit, and VAT.
+
+        :return: A dictionary containing detailed cost breakdown.
+        """
+        # Cost per m2
+        material = {
+            "description": "Crown Dritherm Cavity Slab 37 (Thermal conductivity 0.037 W/mK) glass fibre batt or other "
+                           "equal; as full or partial cavity fill; including cutting and fitting around wall ties and "
+                           "retaining discs",
+            "depth": 75,
+            "thermal_conductivity": 0.037,
+            "prime_cost": 5.17,
+            "material_cost": 5.62,
+            "labour_cost": 2.25,
+            "labour_hours": 0.13
+        }
+
+        material_cost_per_m2 = material["material_cost"]
+        wall_area = self.property.insulation_wall_area
+
+        # This is the amount of material required in m3, assuming a standard 75mm depth
+        volume = 0.075 * wall_area
+
+        base_material_cost = material_cost_per_m2 * wall_area
+        labour_cost = material["labour_cost"] * wall_area
+
+        subtotal_before_profit = base_material_cost + labour_cost
+
+        contingency_cost = subtotal_before_profit * self.CONTINGENCY
+        preliminaries_cost = subtotal_before_profit * self.PRELIMINARIES
+        profit_cost = subtotal_before_profit * self.PROFIT_MARGIN
+
+        subtotal_before_vat = subtotal_before_profit + contingency_cost + preliminaries_cost + profit_cost
+
+        vat_cost = subtotal_before_vat * self.VAT_RATE
+
+        total_cost = subtotal_before_vat + vat_cost
+
+        labour_hours = material["labour_hours"] * wall_area
+
+        return {
+            "total": total_cost,
+            "subtotal": subtotal_before_vat,
+            "vat": vat_cost,
+            "contingency": contingency_cost,
+            "preliminaries": preliminaries_cost,
+            "material": base_material_cost,
+            "profit": profit_cost,
+            "labour_hours": labour_hours
+        }
+
+    def cavity_wall_insulation(self, material):
+        """
+        Calculates the total cost for cavity wall insulation based on material and labor costs,
+        including contingency, preliminaries, profit, and VAT.
+
+        :return: A dictionary containing detailed cost breakdown.
+        """
+        # Cost per m2
+        material = {
+            "description": "Crown Dritherm Cavity Slab 37 (Thermal conductivity 0.037 W/mK) glass fibre batt or other "
+                           "equal; as full or partial cavity fill; including cutting and fitting around wall ties and "
+                           "retaining discs",
+            "depth": 75,
+            "thermal_conductivity": 0.037,
+            "prime_cost": 5.17,
+            "material_cost": 5.62,
+            "labour_cost": 2.25,
+            "labour_hours": 0.13
+        }
+
+        material_cost_per_m2 = material["material_cost"]
+        wall_area = self.property.insulation_wall_area
+
+        # This is the amount of material required in m3, assuming a standard 75mm depth
+        volume = 0.075 * wall_area
+
+        base_material_cost = material_cost_per_m2 * wall_area
+        labour_cost = material["labour_cost"] * wall_area
+
+        subtotal_before_profit = base_material_cost + labour_cost
+
+        contingency_cost = subtotal_before_profit * self.CONTINGENCY
+        preliminaries_cost = subtotal_before_profit * self.PRELIMINARIES
+        profit_cost = subtotal_before_profit * self.PROFIT_MARGIN
+
+        subtotal_before_vat = subtotal_before_profit + contingency_cost + preliminaries_cost + profit_cost
+
+        vat_cost = subtotal_before_vat * self.VAT_RATE
+
+        total_cost = subtotal_before_vat + vat_cost
+
+        labour_hours = material["labour_hours"] * wall_area
+
+        return {
+            "total": total_cost,
+            "subtotal": subtotal_before_vat,
+            "vat": vat_cost,
+            "contingency": contingency_cost,
+            "preliminaries": preliminaries_cost,
+            "material": base_material_cost,
+            "profit": profit_cost,
+            "labour_hours": labour_hours
+        }