diff --git a/backend/app/modelling/property_filters.py b/backend/app/modelling/property_filters.py
index 819ba3420..8c5a26e8f 100644
--- a/backend/app/modelling/property_filters.py
+++ b/backend/app/modelling/property_filters.py
@@ -10,7 +10,9 @@ from dataclasses import dataclass
 from typing import Optional
 
 from pydantic import BaseModel, ConfigDict
-from sqlmodel import Session
+from sqlmodel import Session, col, select
+
+from infrastructure.postgres.property_table import PropertyRow
 
 
 class PropertyGroupFilters(BaseModel):
@@ -41,4 +43,16 @@ def resolve_filtered_property_ids(
     portfolio's rows with ``marked_for_deletion = false``; property_type /
     built_form resolve override → lodged EPC → predicted EPC → legacy columns
     → "Unknown"."""
-    raise NotImplementedError
+    rows = session.exec(
+        select(PropertyRow)
+        .where(PropertyRow.portfolio_id == portfolio_id)
+        # IS NOT TRUE rather than == False: the FE schema defaults the flag,
+        # but a NULL must never silently exclude a property.
+        .where(col(PropertyRow.marked_for_deletion).isnot(True))
+        .order_by(col(PropertyRow.id))
+    ).all()
+    return [
+        FilteredProperty(property_id=row.id, postcode=row.postcode)
+        for row in rows
+        if row.id is not None
+    ]