From 600684f5dfaaedf2a08e7e85b40fd02b96538072 Mon Sep 17 00:00:00 2001
From: Khalim Conn-Kowlessar <kconnkowlessar@gmail.com>
Date: Sat, 20 Jun 2026 14:09:21 +0000
Subject: [PATCH] fix(uvalues): apply metal-frame U 1.6 for 2022-or-later
 windows (RdSAP 10 Table 24, PDF p.51)

Table 24 "Double or triple glazed, 2022 or later" row gives U = 1.4 for
PVC/wooden frames and 1.6 for metal frames. `u_window` returned 1.4 for both,
ignoring the metal-frame variant and under-counting metal-frame heat loss on
post-2022 windows. The 2002-2021 and pre-2002 rows already split PVC/metal
correctly; this aligns the 2022+ row.

Spec-pinned in test_u_window_post_2022_metal_returns_table24_1_6_not_pvc_1_4.
pyright not installed in this container.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
---
 domain/sap10_ml/rdsap_uvalues.py            |  3 ++-
 domain/sap10_ml/tests/test_rdsap_uvalues.py | 12 ++++++++++++
 2 files changed, 14 insertions(+), 1 deletion(-)

diff --git a/domain/sap10_ml/rdsap_uvalues.py b/domain/sap10_ml/rdsap_uvalues.py
index 6b1e35fc..b4ab5de3 100644
--- a/domain/sap10_ml/rdsap_uvalues.py
+++ b/domain/sap10_ml/rdsap_uvalues.py
@@ -1419,7 +1419,8 @@ def u_window(
 
     # double/triple glazing — period bands.
     if installed_year is not None and installed_year >= 2022:
-        return 1.4
+        # Table 24 "2022 or later" row: PVC/wood 1.4, metal 1.6.
+        return 1.6 if metal else 1.4
     if installed_year is not None and installed_year >= 2002:
         return 2.2 if metal else 2.0
     # pre-2002 double/triple default to 12mm gap row.
diff --git a/domain/sap10_ml/tests/test_rdsap_uvalues.py b/domain/sap10_ml/tests/test_rdsap_uvalues.py
index 77de58eb..522ccd52 100644
--- a/domain/sap10_ml/tests/test_rdsap_uvalues.py
+++ b/domain/sap10_ml/tests/test_rdsap_uvalues.py
@@ -1748,6 +1748,18 @@ def test_u_window_post_2022_pvc_returns_low_table24_value() -> None:
     assert result == pytest.approx(1.4, abs=0.001)
 
 
+def test_u_window_post_2022_metal_returns_table24_1_6_not_pvc_1_4() -> None:
+    # Arrange — Table 24 "2022 or later" row (PDF p.51): PVC/wooden frame
+    # 1.4, METAL frame 1.6. The metal frame variant was previously ignored
+    # (1.4 returned for both), under-counting metal-frame heat loss.
+
+    # Act
+    result = u_window(installed_year=2023, glazing_type="double", frame_type="metal")
+
+    # Assert
+    assert result == pytest.approx(1.6, abs=0.001)
+
+
 def test_u_window_falls_back_to_mid_range_when_unknown() -> None:
     # Arrange — nothing known.