diff --git a/lca_carbon_workflow.py b/lca_carbon_workflow.py
index 4d7a101..99c4376 100644
--- a/lca_carbon_workflow.py
+++ b/lca_carbon_workflow.py
@@ -83,10 +83,12 @@ class LCACarbonWorkflow:
               opening.area).calculate_opening_emission())
             print('\t\t\t', opening_emission)
           print('opening_emission', opening_emission)
-        boundary_opening_emission.append(opening_emission)
+        if opening_emission:
+          boundary_opening_emission += opening_emission
         print('boundary_opening_emission', boundary_opening_emission)
-      surface_opening_emission.append(boundary_opening_emission)
-      print('surface_opening_emission', surface_opening_emission)
+      if boundary_opening_emission:
+        surface_opening_emission += boundary_opening_emission
+      print('surface_opening_emission', surface_opening_emission, '\n', sum(surface_opening_emission))
 
   def calculate_emission(self):
     emitted_carbon = []