diff --git a/backend/documents_parser/tests/test_pashub_sap_accuracy.py b/backend/documents_parser/tests/test_pashub_sap_accuracy.py
index 22ce21d08..6dd0cd1b4 100644
--- a/backend/documents_parser/tests/test_pashub_sap_accuracy.py
+++ b/backend/documents_parser/tests/test_pashub_sap_accuracy.py
@@ -118,7 +118,12 @@ _MIN_WITHIN_HALF: float = 0.19
 # instead of silently defaulting to code 693 eff 1.00): correctness fix,
 # 499607224524 +4.0 -> +1.2, observed MAE 1.383 -> 1.381 — too small to
 # tighten the 2-decimal ceiling, within-0.5 unchanged at 20.0%.
-_MAX_SAP_MAE: float = 1.39
+# Ratcheted 1.39 -> 1.37 by the Simplified-RIR common-wall fix: a "Roof room
+# type" (RdSAP §3.9.2) lodgement now bills common walls as `common_wall` at
+# the main-wall U (spec area L x (0.25 + H)) instead of a Detailed `stud_wall`
+# roof surface that dropped to the Table 18 col(4) 2.30 uninsulated default
+# (78/72 North Road, +1.1 SAP each). Observed MAE 1.370, within-0.5 20.0%.
+_MAX_SAP_MAE: float = 1.37
 
 _KNOWN_GAP_REASON = (
     "pashub `from_site_notes` mapper does not int-code a main-heating "