diff --git a/pipeline/transform/join_epc_pp.py b/pipeline/transform/join_epc_pp.py
index 1711952..789fcac 100644
--- a/pipeline/transform/join_epc_pp.py
+++ b/pipeline/transform/join_epc_pp.py
@@ -36,6 +36,12 @@ def main():
             "CONSTRUCTION_AGE_BAND",
         )
         .filter(pl.col("epc_address").is_not_null())
+        .with_columns(
+            pl.when(pl.col("NUMBER_HABITABLE_ROOMS") == 0)
+            .then(None)
+            .otherwise(pl.col("NUMBER_HABITABLE_ROOMS"))
+            .alias("NUMBER_HABITABLE_ROOMS"),
+        )
         .sort("INSPECTION_DATE", descending=True)
         .group_by("epc_address", "POSTCODE")
         .first()