diff --git a/etl/transform/types.py b/etl/transform/types.py
index 896fc4f..de84fad 100644
--- a/etl/transform/types.py
+++ b/etl/transform/types.py
@@ -61,7 +61,7 @@ class Roofs(BaseModel):
 class Floors(BaseModel):
     floor_type: str
     ground_floor_construction: str
-    ground_floor_insulation_type: str
+    ground_floor_insulation_type: Optional[str] = ""
     floor_insulation_thickness_mm: Optional[float] = -1
     u_value_known: bool