diff --git a/asf_heat_pump_suitability/pipeline/prepare_features/epc.py b/asf_heat_pump_suitability/pipeline/prepare_features/epc.py
index c9b386e..2425c2f 100644
--- a/asf_heat_pump_suitability/pipeline/prepare_features/epc.py
+++ b/asf_heat_pump_suitability/pipeline/prepare_features/epc.py
@@ -15,12 +15,14 @@ def add_col_msoa_avg_outdoor_space_property_type(
     Returns:
           pl.DataFrame: EPC dataset with secondary property type mapped from ONS garden size dataset
     """
+    houses = ["Detached", "Semi-Detached", "Terraced (including end-terrace)"]
+
     df = df.with_columns(
-        pl.when(pl.col(ptype_col).str.to_lowercase().str.contains("house"))
+        pl.when(pl.col(ptype_col).is_in(houses))
         .then(pl.lit("Houses"))
         .when(pl.col(ptype_col).str.to_lowercase().str.contains("flat"))
         .then(pl.lit("Flats"))
-        .otherwise(pl.lit(ptype_col))
+        .otherwise(pl.lit("unknown"))
         .alias("msoa_avg_outdoor_space_property_type")
     )