diff --git a/exposurejapan/commercial.py b/exposurejapan/commercial.py
index 11c0b6f64f247b4621d801896a7b3ea3b201eab4..f6ee85f8740a7242276260619d2ff829f6bef407 100644
--- a/exposurejapan/commercial.py
+++ b/exposurejapan/commercial.py
@@ -500,7 +500,7 @@ class CommercialAggregatedExposure(SpatialiteDatabase):
 
             # Get ID of construction material
             if row["construction_material"] == "Unknown":
-                construction_material_id = constants.TOTAL
+                construction_material_id = constants.UNKNOWN
             else:
                 construction_material_id = add_element_and_get_index(
                     row["construction_material"], construction_material_list
@@ -508,7 +508,7 @@ class CommercialAggregatedExposure(SpatialiteDatabase):
 
             # Get ID of basement presence type
             if row["presence_or_absence_basement"] == "Unknown":
-                basement_presence_id = constants.TOTAL
+                basement_presence_id = constants.UNKNOWN
             else:
                 basement_presence_id = add_element_and_get_index(
                     row["presence_or_absence_basement"], basement_presence_list
@@ -516,7 +516,7 @@ class CommercialAggregatedExposure(SpatialiteDatabase):
 
             # Get ID of earthquake resistance code presence type
             if row["earthquake_resistance_std"] == "Unknown":
-                eq_resistance_code_presence_id = constants.TOTAL
+                eq_resistance_code_presence_id = constants.UNKNOWN
             else:
                 eq_resistance_code_presence_id = add_element_and_get_index(
                     row["earthquake_resistance_std"], eq_resistance_code_presence_list
@@ -524,7 +524,7 @@ class CommercialAggregatedExposure(SpatialiteDatabase):
 
             # Get ID of total floor area (in square meters) range
             if row["total_floor_area"] == "Unknown":
-                total_floor_area_id = constants.TOTAL
+                total_floor_area_id = constants.UNKNOWN
             else:
                 total_floor_area_id = add_element_and_get_index(
                     row["total_floor_area"], total_floor_area_list
diff --git a/exposurejapan/constants.py b/exposurejapan/constants.py
index e1e6b8664deff9d7ce8a1f98f56116399becc42b..1d0afcf99045188fafcbb09ad2112964775a63b2 100644
--- a/exposurejapan/constants.py
+++ b/exposurejapan/constants.py
@@ -108,3 +108,6 @@ NUMBER_DWELLING_SIZES = 6
 
 # Constant numbers for import of dwelling-size data to DwellingFloorspace table
 FLOORSPACE_PER_DWELLING_DWELLING_SIZES = 13
+
+# Constant number for Unknown values while importing commercial building numbers data
+UNKNOWN = -1