diff --git a/pyproject.toml b/pyproject.toml
index 7bf9dbe..fea21af 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -1,6 +1,6 @@
 [project]
 name = "osut"
-version = "0.8.2"
+version = "0.9.0"
 description = "OpenStudio SDK utilities for Python"
 readme = "README.md"
 requires-python = ">=3.2"
diff --git a/src/osut/osut.py b/src/osut/osut.py
index 582df1e..7f2f7bf 100644
--- a/src/osut/osut.py
+++ b/src/osut/osut.py
@@ -103,20 +103,22 @@ class _CN:
 # Default inside + outside air film resistances (m2.K/W).
 _film = dict(
       shading = 0.000, # NA
-    partition = 0.150, # uninsulated wood- or steel-framed wall
+      ceiling = 0.266, # interzone floor/ceiling
+    partition = 0.239, # interzone wall partition
          wall = 0.150, # un/insulated wall
-         roof = 0.140, # un/insulated roof
-        floor = 0.190, # un/insulated (exposed) floor
+         roof = 0.135, # un/insulated roof
+        floor = 0.192, # un/insulated (exposed) floor
      basement = 0.120, # un/insulated basement wall
-         slab = 0.160, # un/insulated basement slab or slab-on-grade
+         slab = 0.162, # un/insulated basement slab or slab-on-grade
          door = 0.150, # standard, 45mm insulated steel (opaque) door
        window = 0.150, # vertical fenestration, e.g. glazed doors, windows
-     skylight = 0.140  # e.g. domed 4' x 4' skylight
+     skylight = 0.135  # e.g. domed 4' x 4' skylight
     )
 
 # Default (~1980s) envelope Uo (W/m2•K), based on surface type.
 _uo = dict(
       shading = None,  # N/A
+      ceiling = None,  # N/A
     partition = None,  # N/A
          wall = 0.384, # rated R14.8 hr•ft2F/Btu
          roof = 0.327, # rated R17.6 hr•ft2F/Btu
@@ -309,6 +311,64 @@ def clamp(value, minimum, maximum) -> float:
     return value
 
 
+def filmResistances(type="wall", tilt=2*math.pi) -> float:
+    """Returns surface air film resistance(s). Surface tilt-dependent values
+    are returned if a valid surface tilt [0, PI] is provided. Otherwise,
+    generic tilt-independent air film resistances are returned instead.
+
+    Args:
+        type (string):
+            Surface type, e.g. "roof", "wall", "partition", "ceiling"
+        tilt (float):
+            Surface tilt (in rad), optional
+
+    Returns:
+        float: Surface air film resistance(s)
+        0.0: If invalid inputs (see logs).
+
+    """
+    mth = "osut.filmResistances"
+
+    try:
+        tilt = float(tilt)
+    except:
+        return oslg.mismatch("surface tilt", tilt, float, mth, CN.DBG, 0.0)
+
+    try:
+        type = str(type)
+    except:
+        return oslg.mismatch("surface type", type, str, mth, CN.DBG, 0.0)
+
+    if type not in film():
+        return oslg.invalid("surface type", mth, 1, CN.DBG, 0.0)
+
+    # Generic, tilt-independent values.
+    r = film()[type]
+
+    if type == "shading":
+        return r
+    elif 0.0 <= tilt <= math.pi:
+        r = openstudio.model.PlanarSurface.stillAirFilmResistance(tilt)
+
+        if type == "basement" or type == "slab":
+            return r
+        elif type == "ceiling" or type == "partition":
+            # Interzone. Fetch reciprocal tilt, e.g. if tilt == 0°, tiltx = 180°
+            tiltx = tilt + math.pi
+
+            # Assuming tilt is contrained [0°, 180°] - constrain tiltx [0° 180°]:
+            #   e.g. tiltx == 210° if tilt ==  30°, so convert tiltx to 150°
+            #   e.g. tiltx == 330° if tilt == 150°, so convert tiltx to  30°
+            #   e.g. tiltx == 275° if tilt ==  95°, so convert tiltx to  85°
+            if tiltx > math.pi: tiltx = math.pi - tilt
+
+            r += openstudio.model.PlanarSurface.stillAirFilmResistance(tiltx)
+        else:
+            r += 0.03 # "MOVINGAIR_15MPH"
+
+    return r
+
+
 def areStandardOpaqueLayers(lc=None) -> bool:
     """Validates if every material in a layered construction is standard/opaque.
 
@@ -715,7 +775,7 @@ def resetUo(lc=None, film=None, index=None, uo=None, uniq=False) -> float:
         mt.setName(id)
 
         if not mt.setThermalResistance(r):
-            oslg.log(CN.WRN, "Failed to reset %s: RSi%.2f (%s)" % (id, r, mth))
+            oslg.log(CN.DBG, "Failed to reset %s: RSi%.2f (%s)" % (id, r, mth))
             return 0.0
 
         lc.setLayer(index, mt)
@@ -745,12 +805,12 @@ def resetUo(lc=None, film=None, index=None, uo=None, uniq=False) -> float:
         mt.setName(id)
 
         if not mt.setThermalConductivity(k):
-            oslg.log(CN.WRN, "Failed to reset %s: K%.3f (%s)" % (id, k, mth))
+            oslg.log(CN.DBG, "Failed to reset %s: K%.3f (%s)" % (id, k, mth))
             return 0.0
 
         if not mt.setThickness(d):
             d = int(d*1000)
-            oslg.log(CN.WRN, "Failed to reset %s: %dmm (%s)" % (id, d, mth))
+            oslg.log(CN.DBG, "Failed to reset %s: %dmm (%s)" % (id, d, mth))
             return 0.0
 
         lc.setLayer(index, mt)
@@ -836,8 +896,36 @@ def genConstruction(model=None, specs=dict()):
         a["compo"]["d"  ] = d
         a["compo"]["id" ] = "OSut." + mt + ".%03d" % int(d * 1000)
 
+    elif specs["type"] == "ceiling":
+        if specs["clad"] != "none":
+            mt = "concrete"
+            d  = 0.015
+            if specs["clad"] == "light":  mt = "material"
+            if specs["clad"] == "medium":  d = 0.100
+            if specs["clad"] == "heavy":   d = 0.200
+            a["clad"]["mat"] = mats()[mt]
+            a["clad"]["d"  ] = d
+            a["clad"]["id" ] = "OSut." + mt + ".%03d" % int(d * 1000)
+
+        mt = "mineral"
+        d  = 0.100
+        if specs["frame"] == "medium": mt = "polyiso"
+        if specs["frame"] == "heavy":  mt = "cellulose"
+        if not u:                      mt = "material"
+        if not u:                       d = 0.015
+        a["compo"]["mat"] = mats()[mt]
+        a["compo"]["d"  ] = d
+        a["compo"]["id" ] = "OSut." + mt + ".%03d" % int(d * 1000)
+
+        if specs["finish"] != "none":
+            mt = "material"
+            d  = 0.015
+            a["finish"]["mat"] = mats()[mt]
+            a["finish"]["d"  ] = d
+            a["finish"]["id" ] = "OSut." + mt + ".%03d" % int(d * 1000)
+
     elif specs["type"] == "partition":
-        if not specs["clad"] == "none":
+        if specs["clad"] != "none":
             mt = "drywall"
             d  = 0.015
             a["clad"]["mat"] = mats()[mt]
@@ -855,7 +943,7 @@ def genConstruction(model=None, specs=dict()):
         a["compo"]["d"  ] = d
         a["compo"]["id" ] = "OSut." + mt + ".%03d" % int(d * 1000)
 
-        if not specs["finish"] == "none":
+        if specs["finish"] != "none":
             mt = "drywall"
             d  = 0.015
             a["finish"]["mat"] = mats()[mt]
@@ -863,7 +951,7 @@ def genConstruction(model=None, specs=dict()):
             a["finish"]["id" ] = "OSut." + mt + ".%03d" % int(d * 1000)
 
     elif specs["type"] == "wall":
-        if not specs["clad"] == "none":
+        if specs["clad"] != "none":
             mt = "material"
             d  = 0.100
             if specs["clad"] == "medium": mt = "brick"
@@ -893,7 +981,7 @@ def genConstruction(model=None, specs=dict()):
         a["compo"]["d"  ] = d
         a["compo"]["id" ] = "OSut." + mt + ".%03d" % int(d * 1000)
 
-        if not specs["finish"] == "none":
+        if specs["finish"] != "none":
             mt = "concrete"
             d  = 0.015
             if specs["finish"] == "light":  mt = "drywall"
@@ -904,7 +992,7 @@ def genConstruction(model=None, specs=dict()):
             a["finish"]["id" ] = "OSut." + mt + ".%03d" % int(d * 1000)
 
     elif specs["type"] == "roof":
-        if not specs["clad"] == "none":
+        if specs["clad"] != "none":
             mt = "concrete"
             d  = 0.015
             if specs["clad"] == "light": mt = "material"
@@ -924,7 +1012,7 @@ def genConstruction(model=None, specs=dict()):
         a["compo"]["d"  ] = d
         a["compo"]["id" ] = "OSut." + mt + ".%03d" % int(d * 1000)
 
-        if not specs["finish"] == "none":
+        if specs["finish"] != "none":
             mt = "concrete"
             d  = 0.015
             if specs["finish"] == "light":  mt = "drywall"
@@ -935,7 +1023,7 @@ def genConstruction(model=None, specs=dict()):
             a["finish"]["id" ] = "OSut." + mt + ".%03d" % int(d * 1000)
 
     elif specs["type"] == "floor":
-        if not specs["clad"] == "none":
+        if specs["clad"] != "none":
             mt = "material"
             d  = 0.015
             a["clad"]["mat"] = mats()[mt]
@@ -952,7 +1040,7 @@ def genConstruction(model=None, specs=dict()):
         a["compo"]["d"  ] = d
         a["compo"]["id" ] = "OSut." + mt + ".%03d" % int(d * 1000)
 
-        if not specs["finish"] == "none":
+        if specs["finish"] != "none":
             mt = "concrete"
             d  = 0.015
             if specs["finish"] == "light": mt = "material"
@@ -969,7 +1057,7 @@ def genConstruction(model=None, specs=dict()):
         a["clad"]["d"  ] = d
         a["clad"]["id" ] = "OSut." + mt + ".%03d" % int(d * 1000)
 
-        if not specs["frame"] == "none":
+        if specs["frame"] != "none":
             mt = "polyiso"
             d  = 0.025
             a["sheath"]["mat"] = mats()[mt]
@@ -983,7 +1071,7 @@ def genConstruction(model=None, specs=dict()):
         a["compo"]["d"  ] = d
         a["compo"]["id" ] = "OSut." + mt + ".%03d" % int(d * 1000)
 
-        if not specs["finish"] == "none":
+        if specs["finish"] != "none":
             mt = "material"
             d  = 0.015
             a["finish"]["mat"] = mats()[mt]
@@ -991,7 +1079,7 @@ def genConstruction(model=None, specs=dict()):
             a["finish"]["id" ] = "OSut." + mt + ".%03d" % int(d * 1000)
 
     elif specs["type"] == "basement":
-        if not specs["clad"] == "none":
+        if specs["clad"] != "none":
             mt = "concrete"
             d  = 0.100
             if specs["clad"] == "light": mt = "material"
@@ -1018,7 +1106,7 @@ def genConstruction(model=None, specs=dict()):
             a["sheath"]["d"  ] = d
             a["sheath"]["id" ] = "OSut." + mt + ".%03d" % int(d * 1000)
 
-            if not specs["finish"] == "none":
+            if specs["finish"] != "none":
                 mt = "mineral"
                 d  = 0.075
                 a["compo"]["mat"] = mats()[mt]
@@ -2711,10 +2799,10 @@ def availabilitySchedule(model=None, avl=""):
         if not l.lowerLimitValue(): continue
         if not l.upperLimitValue(): continue
         if not l.numericType(): continue
-        if not int(l.lowerLimitValue().get()) == 0: continue
-        if not int(l.upperLimitValue().get()) == 1: continue
-        if not l.numericType().get().lower() == "discrete": continue
-        if not l.unitType().lower() == "availability": continue
+        if int(l.lowerLimitValue().get()) != 0: continue
+        if int(l.upperLimitValue().get()) != 1: continue
+        if l.numericType().get().lower() != "discrete": continue
+        if l.unitType().lower() != "availability": continue
         if ide != "hvac operation scheduletypelimits": continue
 
         limits = l
diff --git a/tests/test_osut.py b/tests/test_osut.py
index 1719699..5e9fd48 100644
--- a/tests/test_osut.py
+++ b/tests/test_osut.py
@@ -60,8 +60,8 @@ def test02_tuples(self):
 
     def test03_dictionaries(self):
         self.assertEqual(len(osut.mats()),9)
-        self.assertEqual(len(osut.film()),10)
-        self.assertEqual(len(osut.uo()),10)
+        self.assertEqual(len(osut.film()),11)
+        self.assertEqual(len(osut.uo()),11)
         self.assertTrue("concrete" in osut.mats())
         self.assertTrue("skylight" in osut.film())
         self.assertTrue("skylight" in osut.uo())
@@ -160,26 +160,6 @@ def test05_construction_generation(self):
         self.assertEqual(o.status(), 0)
         del model
 
-        # Alternative to (uninsulated) partition (more inputs, same outcome).
-        specs = dict(type="wall", clad="none", uo=None)
-        model = openstudio.model.Model()
-        c = osut.genConstruction(model, specs)
-        self.assertEqual(o.status(), 0)
-        self.assertFalse(o.logs())
-        self.assertTrue(c)
-        self.assertTrue(isinstance(c, openstudio.model.Construction))
-        self.assertEqual(c.nameString(), "OSut.CON.wall")
-        self.assertTrue(c.layers())
-        self.assertEqual(len(c.layers()), 3)
-        self.assertEqual(c.layers()[0].nameString(), "OSut.drywall.015")
-        self.assertEqual(c.layers()[1].nameString(), "OSut.material.015")
-        self.assertEqual(c.layers()[2].nameString(), "OSut.drywall.015")
-        self.assertTrue("uo" in specs)
-        self.assertEqual(specs["uo"], None)
-        self.assertFalse(o.logs())
-        self.assertEqual(o.status(), 0)
-        del model
-
         # Insulated partition variant.
         specs = dict(type="partition", uo=0.214)
         model = openstudio.model.Model()
@@ -192,7 +172,7 @@ def test05_construction_generation(self):
         self.assertTrue(c.layers())
         self.assertEqual(len(c.layers()), 3)
         self.assertEqual(c.layers()[0].nameString(), "OSut.drywall.015")
-        self.assertEqual(c.layers()[1].nameString(), "OSut:K0.023:100")
+        self.assertEqual(c.layers()[1].nameString(), "OSut:K0.024:100")
         self.assertEqual(c.layers()[2].nameString(), "OSut.drywall.015")
         self.assertTrue("uo" in specs)
         self.assertAlmostEqual(specs["uo"], 0.214, places=2)
@@ -906,13 +886,6 @@ def test08_holds_constructions(self):
         model = model.get()
         mdl   = openstudio.model.Model()
 
-        # cl1 = openstudio.model.DefaultConstructionSet
-        # cl2 = openstudio.model.LayeredConstruction
-        # cl2 = openstudio.model.Construction
-        # id1 = cl1.__name__
-        # id2 = cl2.__name__
-        # id3 = cl3.__name__
-
         t1 = "RoofCeiling"
         t2 = "Wall"
         t3 = "Floor"
@@ -1127,95 +1100,7 @@ def test10_glazing_airfilms(self):
 
         del model
 
-    def test11_rsi(self):
-        o = osut.oslg
-        self.assertEqual(o.status(), 0)
-        self.assertEqual(o.reset(DBG), DBG)
-        self.assertEqual(o.level(), DBG)
-
-        version = int("".join(openstudio.openStudioVersion().split(".")))
-        translator = openstudio.osversion.VersionTranslator()
-
-        path  = openstudio.path("./tests/files/osms/out/seb2.osm")
-        model = translator.loadModel(path)
-        self.assertTrue(model)
-        model = model.get()
-
-        m0  = "osut.rsi"
-        m1 = "'lc' str? expecting LayeredConstruction (%s)" % m0
-        m2 = "'lc' NoneType? expecting LayeredConstruction (%s)" % m0
-        m3 = "Negative 'film' (%s)" % m0
-        m4 = "'film' NoneType? expecting float (%s)" % m0
-        m5 = "Negative 'temp K' (%s)" % m0
-        m6 = "'temp K' NoneType? expecting float (%s)" % m0
-
-        for s in model.getSurfaces():
-            if not s.isPartOfEnvelope(): continue
-
-            lc = s.construction()
-            self.assertTrue(lc)
-            lc = lc.get().to_LayeredConstruction()
-            self.assertTrue(lc)
-            lc = lc.get()
-
-            if s.isGroundSurface(): # 4x slabs on grade in SEB model
-                self.assertAlmostEqual(s.filmResistance(), 0.160, places=3)
-                self.assertAlmostEqual(osut.rsi(lc, s.filmResistance()), 0.448, places=3)
-                self.assertEqual(o.status(), 0)
-            else:
-                if s.surfaceType() == "Wall":
-                    self.assertAlmostEqual(s.filmResistance(), 0.150, places=3)
-                    self.assertAlmostEqual(osut.rsi(lc, s.filmResistance()), 2.616, places=3)
-                    self.assertEqual(o.status(), 0)
-                else: # RoofCeiling
-                    self.assertAlmostEqual(s.filmResistance(), 0.136, places=3)
-                    self.assertAlmostEqual(osut.rsi(lc, s.filmResistance()), 5.631, places=3)
-                    self.assertEqual(o.status(), 0)
-
-        # Stress tests.
-        self.assertAlmostEqual(osut.rsi("", 0.150), 0, places=2)
-        self.assertTrue(o.is_debug())
-        self.assertEqual(len(o.logs()), 1)
-        self.assertEqual(o.logs()[0]["message"], m1)
-        self.assertEqual(o.clean(), DBG)
-
-        self.assertAlmostEqual(osut.rsi(None, 0.150), 0, places=2)
-        self.assertTrue(o.is_debug())
-        self.assertEqual(len(o.logs()), 1)
-        self.assertEqual(o.logs()[0]["message"], m2)
-        self.assertEqual(o.clean(), DBG)
-
-        lc = model.getLayeredConstructionByName("SLAB-ON-GRADE-FLOOR")
-        self.assertTrue(lc)
-        lc = lc.get()
-
-        self.assertAlmostEqual(osut.rsi(lc, -1), 0, places=0)
-        self.assertTrue(o.is_error())
-        self.assertEqual(len(o.logs()), 1)
-        self.assertEqual(o.logs()[0]["message"], m3)
-        self.assertEqual(o.clean(), DBG)
-
-        self.assertAlmostEqual(osut.rsi(lc, None), 0, places=0)
-        self.assertTrue(o.is_debug())
-        self.assertEqual(len(o.logs()), 1)
-        self.assertEqual(o.logs()[0]["message"], m4)
-        self.assertEqual(o.clean(), DBG)
-
-        self.assertAlmostEqual(osut.rsi(lc, 0.150, -300), 0, places=0)
-        self.assertTrue(o.is_error())
-        self.assertEqual(len(o.logs()), 1)
-        self.assertEqual(o.logs()[0]["message"], m5)
-        self.assertEqual(o.clean(), DBG)
-
-        self.assertAlmostEqual(osut.rsi(lc, 0.150, None), 0, places=0)
-        self.assertTrue(o.is_debug())
-        self.assertEqual(len(o.logs()), 1)
-        self.assertEqual(o.logs()[0]["message"], m6)
-        self.assertEqual(o.clean(), DBG)
-
-        del model
-
-    def test12_insulating_layer(self):
+    def test11_insulating_layer(self):
         o = osut.oslg
         self.assertEqual(o.status(), 0)
         self.assertEqual(o.reset(DBG), DBG)
@@ -1302,7 +1187,7 @@ def test12_insulating_layer(self):
 
         del model
 
-    def test13_spandrels(self):
+    def test12_spandrels(self):
         o = osut.oslg
         self.assertEqual(o.status(), 0)
         self.assertEqual(o.reset(DBG), DBG)
@@ -1362,7 +1247,7 @@ def test13_spandrels(self):
 
         del model
 
-    def test14_schedule_ruleset_minmax(self):
+    def test13_schedule_ruleset_minmax(self):
         o = osut.oslg
         self.assertEqual(o.status(), 0)
         self.assertEqual(o.reset(DBG), DBG)
@@ -1443,7 +1328,7 @@ def test14_schedule_ruleset_minmax(self):
 
         del model
 
-    def test15_schedule_constant_minmax(self):
+    def test14_schedule_constant_minmax(self):
         o = osut.oslg
         self.assertEqual(o.status(), 0)
         self.assertEqual(o.reset(DBG), DBG)
@@ -1524,7 +1409,7 @@ def test15_schedule_constant_minmax(self):
 
         del model
 
-    def test16_schedule_compact_minmax(self):
+    def test15_schedule_compact_minmax(self):
         o = osut.oslg
         self.assertEqual(o.status(), 0)
         self.assertEqual(o.reset(DBG), DBG)
@@ -1603,7 +1488,7 @@ def test16_schedule_compact_minmax(self):
 
         del model
 
-    def test17_minmax_heatcool_setpoints(self):
+    def test16_minmax_heatcool_setpoints(self):
         o = osut.oslg
         self.assertEqual(o.status(), 0)
         self.assertEqual(o.reset(DBG), DBG)
@@ -1791,7 +1676,7 @@ def test17_minmax_heatcool_setpoints(self):
 
         del model
 
-    def test18_hvac_airloops(self):
+    def test17_hvac_airloops(self):
         o = osut.oslg
         self.assertEqual(o.status(), 0)
         self.assertEqual(o.reset(DBG), DBG)
@@ -1836,7 +1721,7 @@ def test18_hvac_airloops(self):
 
         del model
 
-    def test19_vestibules(self):
+    def test18_vestibules(self):
         o = osut.oslg
         self.assertEqual(o.status(), 0)
         self.assertEqual(o.reset(DBG), DBG)
@@ -1906,7 +1791,7 @@ def test19_vestibules(self):
 
         del model
 
-    def test20_setpoints_plenums_attics(self):
+    def test19_setpoints_plenums_attics(self):
         o = osut.oslg
         self.assertEqual(o.status(), 0)
         self.assertEqual(o.reset(DBG), DBG)
@@ -2139,7 +2024,7 @@ def test20_setpoints_plenums_attics(self):
         # --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- #
         # Consider adding LargeOffice model to test SDK's "isPlenum" ... @todo
 
-    def test21_availability_schedules(self):
+    def test20_availability_schedules(self):
         o = osut.oslg
         self.assertEqual(o.status(), 0)
         self.assertEqual(o.reset(DBG), DBG)
@@ -2353,7 +2238,7 @@ def test21_availability_schedules(self):
 
         del model
 
-    def test22_model_transformation(self):
+    def test21_model_transformation(self):
         o = osut.oslg
         self.assertEqual(o.status(), 0)
         self.assertEqual(o.reset(DBG), DBG)
@@ -2682,7 +2567,7 @@ def test22_model_transformation(self):
         # if o.logs(): print(mod1.logs())
         self.assertEqual(o.status(), 0)
 
-    def test23_fits_overlaps(self):
+    def test22_fits_overlaps(self):
         o = osut.oslg
         self.assertEqual(o.status(), 0)
         self.assertEqual(o.reset(DBG), DBG)
@@ -3246,7 +3131,7 @@ def test23_fits_overlaps(self):
         del model
         self.assertEqual(o.clean(), DBG)
 
-    def test24_triangulation(self):
+    def test23_triangulation(self):
         o = osut.oslg
         self.assertEqual(o.status(), 0)
         self.assertEqual(o.reset(DBG), DBG)
@@ -3288,7 +3173,7 @@ def test24_triangulation(self):
         # [ 0, 10, 0]
         # [20,  0, 0]
 
-    def test25_segments_triads_orientation(self):
+    def test24_segments_triads_orientation(self):
         o = osut.oslg
         self.assertEqual(o.status(), 0)
         self.assertEqual(o.reset(DBG), DBG)
@@ -3641,7 +3526,7 @@ def test25_segments_triads_orientation(self):
 
         self.assertEqual(len(matches), 1)
 
-    def test26_ulc_blc(self):
+    def test25_ulc_blc(self):
         o = osut.oslg
         self.assertEqual(o.status(), 0)
         self.assertEqual(o.reset(DBG), DBG)
@@ -3814,7 +3699,7 @@ def test26_ulc_blc(self):
         # [70, 45, 0]
         # [ 0, 45, 0]
 
-    def test27_polygon_attributes(self):
+    def test26_polygon_attributes(self):
         o = osut.oslg
         self.assertEqual(o.status(), 0)
         self.assertEqual(o.reset(INF), INF)
@@ -4030,7 +3915,7 @@ def test27_polygon_attributes(self):
         self.assertFalse(osut.isClockwise(v))
         self.assertEqual(o.status(), 0)
 
-    def test28_subsurface_insertions(self):
+    def test27_subsurface_insertions(self):
         # Examples of how to harness OpenStudio's Boost geometry methods to
         # safely insert subsurfaces along rotated/tilted/slanted base surfaces.
         # --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- #
@@ -4375,7 +4260,7 @@ def test28_subsurface_insertions(self):
         del model
         self.assertEqual(o.clean(), DBG)
 
-    def test29_surface_width_height(self):
+    def test28_surface_width_height(self):
         o = osut.oslg
         self.assertEqual(o.status(), 0)
         self.assertEqual(o.reset(DBG), DBG)
@@ -4464,7 +4349,7 @@ def test29_surface_width_height(self):
         del model
         self.assertEqual(o.status(), 0)
 
-    def test30_wwr_insertions(self):
+    def test29_wwr_insertions(self):
         o = osut.oslg
         self.assertEqual(o.status(), 0)
         self.assertEqual(o.reset(DBG), DBG)
@@ -4678,7 +4563,7 @@ def test30_wwr_insertions(self):
         del model
         self.assertEqual(o.status(), 0)
 
-    def test31_convexity(self):
+    def test30_convexity(self):
         o = osut.oslg
         self.assertEqual(o.status(), 0)
         self.assertEqual(o.reset(INF), INF)
@@ -4864,7 +4749,7 @@ def test31_convexity(self):
         del model
         self.assertEqual(o.status(), 0)
 
-    def test32_outdoor_roofs(self):
+    def test31_outdoor_roofs(self):
         o = osut.oslg
         self.assertEqual(o.status(), 0)
         self.assertEqual(o.reset(INF), INF)
@@ -4957,7 +4842,7 @@ def test32_outdoor_roofs(self):
         del model
         self.assertEqual(o.status(), 0)
 
-    def test33_leader_line_anchors_inserts(self):
+    def test32_leader_line_anchors_inserts(self):
         o = osut.oslg
         self.assertEqual(o.status(), 0)
         self.assertEqual(o.reset(DBG), DBG)
@@ -5096,7 +4981,7 @@ def test33_leader_line_anchors_inserts(self):
         #   [ 0, 14, 0] ... vs [20,  2, 20]
         #   [ 0,  0, 0] ... vs [20, 16, 20]
 
-    def test34_generated_skylight_wells(self):
+    def test33_generated_skylight_wells(self):
         o = osut.oslg
         self.assertEqual(o.status(), 0)
         self.assertEqual(o.reset(DBG), DBG)
@@ -5255,9 +5140,10 @@ def test34_generated_skylight_wells(self):
         self.assertAlmostEqual(round(ratio, 2), srr)
 
         # Reset attic default construction set for insulated interzone walls.
+        flm  = osut.filmResistances("partition")
         opts = dict(type="partition", uo=0.3)
         construction = osut.genConstruction(model, opts)
-        self.assertAlmostEqual(osut.rsi(construction, 0.150), 1/0.3, places=2)
+        self.assertAlmostEqual(osut.rsi(construction, flm), 1/0.3, places=2)
         self.assertTrue(ia_set.setWallConstruction(construction))
         if o.logs(): print(o.logs())
 
@@ -5594,7 +5480,7 @@ def test34_generated_skylight_wells(self):
         self.assertEqual(o.status(), 0)
         del model
 
-    def test35_facet_retrieval(self):
+    def test34_facet_retrieval(self):
         o = osut.oslg
         self.assertEqual(o.status(), 0)
         self.assertEqual(o.reset(DBG), DBG)
@@ -5667,6 +5553,396 @@ def test35_facet_retrieval(self):
 
         del model
 
+    def test35_rsi(self):
+        o = osut.oslg
+        self.assertEqual(o.status(), 0)
+        self.assertEqual(o.reset(DBG), DBG)
+        self.assertEqual(o.level(), DBG)
+
+        version = int("".join(openstudio.openStudioVersion().split(".")))
+        translator = openstudio.osversion.VersionTranslator()
+
+        # PlanarSurface method 'filmResistance' reports standard interior or
+        # exterior air film resistances for DISCRETE tilts, per ASHRAE Fundamentals.
+        #   https://github.com/NatLabRockies/OpenStudio/blob/
+        #   8008ef767fdc0f9d3dd3fabd383da15d009aef76/src/model/
+        #   PlanarSurface.cpp#L843
+
+        # EnergyPlus reported film resistances for INTERZONE walls.
+        #   - insulated INTERZONE skylight well walls:
+        #     - U    with film: 0.292 (R    with film: 3.425)
+        #     - U without film: 0.314 (R without film: 3.185)
+        #   TOTAL film resistance = 0.240 (~same as OpenStudio)
+        #
+        # ... vs other INTERZONE walls:
+        #     - U    with film: 2.511 (R    with film: 0.398)
+        #     - U without film: 6.299 (R without film: 0.159)
+        #   TOTAL film resistance = 0.239 (same as OpenStudio)
+
+        # Surface type identifiers to fetch filmResistance values.
+        fts = dict()
+        fts["STILLAIR_HORIZONTALSURFACE_HEATFLOWSUPWARD"  ] = 0.107427212046
+        fts["STILLAIR_45DEGREESURFACE_HEATFLOWSUPWARD"    ] = 0.109188313883
+        fts["STILLAIR_VERTICALSURFACE"                    ] = 0.119754924904
+        fts["STILLAIR_45DEGREESURFACE_HEATFLOWSDOWNWARD"  ] = 0.133843739599
+        fts["STILLAIR_HORIZONTALSURFACE_HEATFLOWSDOWNWARD"] = 0.162021368988
+        fts["MOVINGAIR_15MPH"                             ] = 0.029938731226
+        fts["MOVINGAIR_7P5MPH"                            ] = 0.044027545921
+
+        for i in list(openstudio.model.FilmResistanceType.getValues()):
+            t1 = openstudio.model.FilmResistanceType(i)
+            t2 = openstudio.model.FilmResistanceType(list(fts.keys())[i])
+            r  = openstudio.model.PlanarSurface.filmResistance(t1)
+            self.assertEqual(t1, t2)
+            self.assertAlmostEqual(r, list(fts.values())[i])
+
+            if i > 4: continue
+            # PlanarSurface method 'stillAirFilmResistance' supports a CONTINUOUS
+            # tilt-dependent interior air film resistance.
+            #   https://github.com/NatLabRockies/OpenStudio/blob/
+            #   8008ef767fdc0f9d3dd3fabd383da15d009aef76/src/model/
+            #   PlanarSurface.cpp#L867
+            deg = i * 45
+            rad = deg * math.pi/180.0
+            rsi = openstudio.model.PlanarSurface.stillAirFilmResistance(rad)
+            # per = 100 * (r - rsi) / r
+            # print(i, deg, r, rsi, per)
+            # 0:   0: 0.10743 0.10604  1.29
+            # 1:  45: 0.10919 0.10944 -0.23
+            # 2:  90: 0.11975 0.11965  0.09
+            # 3: 135: 0.13384 0.13665 -2.10
+            # 4: 180: 0.16202 0.16045  0.97
+            if deg < 45 or deg > 90: continue
+
+            # The method is used for (opaque) Surfaces. The correlation/regression
+            # isn't perfect, yet appears fairly reliable for intermediate angles
+            # between ~0° and 90°.
+            self.assertAlmostEqual(rsi, r, places=3)
+
+        # Surface class method 'filmResistance' is different (than PlanarSurface).
+        # It reports the sum of interior and exterior surface air film resistances,
+        # specific to a given surface.
+        #   https://github.com/NatLabRockies/OpenStudio/blob/
+        #   8008ef767fdc0f9d3dd3fabd383da15d009aef76/src/model/
+        #   Surface.cpp#L1400-L1419
+        #
+        # The method relies on 'isPartOfEnvelope', which unfortunately returns
+        # FALSE for insulated INTERZONE surfaces, e.g.:
+        #   - floors of an UNCONDITIONED attic
+        #   - ceiling of an UNCONDITIONED crawlspace
+        #
+        # These are definitely envelope surfaces.
+        #   https://github.com/NatLabRockies/OpenStudio/blob/
+        #   8008ef767fdc0f9d3dd3fabd383da15d009aef76/src/model/
+        #   Surface.cpp#L1243-L1247
+        #
+        # For INTERZONE surfaces, 'filmResistance' simply doubles the reported still
+        # air (interior) film resistance. The solution either underestimates or
+        # overestimates calculated surface air film resistances for non-vertical
+        # surfaces. Although such an approximation is less of an issue when dealing
+        # with highly insulated constructions, caution may be required when
+        # attempting to accommodate key standards like ASHRAE 90.1:
+        #
+        # "building envelope" (90.1 2022, 2025):
+        #   "the EXTERIOR plus the SEMIEXTERIOR portions of a building. For the
+        #    purposes of determining building envelope requirements, the
+        #    classifications are defined as follows:
+        #      - EXTERIOR building envelope: the elements of a building that
+        #        separate CONDITIONED spaces from the exterior.
+        #      - SEMIEXTERIOR building envelope: the elements of a building that
+        #        separate CONDITIONED space from UNCONDITIONED space or that enclose
+        #        SEMIHEATED spaces through which thermal energy may be transferred
+        #        to or from the EXTERIOR, to or from UNCONDITIONED spaces, or to or
+        #        from CONDITIONED spaces."
+        #
+        # This issue is discussed here:
+        #   https://github.com/NatLabRockies/EnergyPlus/issues/9470
+        #
+        # And in part discussed here:
+        #  https://www.ashrae.org/file%20library/technical%20resources/
+        #  standards%20and%20guidelines/standards%20intepretations/
+        #  ic-90.1-2019-8.pdf
+
+        # Testing this outcome, first with an UNCONDITIONED attic case.
+        self.assertEqual(o.clean(), DBG)
+
+        path  = openstudio.path("./tests/files/osms/out/office_attic.osm")
+        model = translator.loadModel(path)
+        self.assertTrue(model)
+        model = model.get()
+
+        attic = model.getSpaceByName("Attic")
+        self.assertTrue(attic)
+        attic = attic.get()
+        self.assertTrue(osut.isUnconditioned(attic))
+
+        # Test attic (insulated) floors, then their adjacent ceilings.
+        for surface in model.getSurfaces():
+            if surface.surfaceType().lower() != "floor": continue
+            if surface.outsideBoundaryCondition().lower() != "surface": continue
+
+            space = surface.space()
+            self.assertTrue(space)
+            space = space.get()
+            self.assertEqual(space, attic)
+
+            id = surface.nameString()
+            self.assertIn("attic_floor", id.lower())
+
+            # A surface's 'tilt' points outward (from its parent space), e.g. a
+            # horizontal attic floor faces downward, or 180°.
+            tilt = surface.tilt()
+            self.assertAlmostEqual(tilt, math.pi, places=4)
+
+            r1 = openstudio.model.PlanarSurface.stillAirFilmResistance(tilt) * 2
+            r2 = surface.filmResistance()
+            r3 = osut.filmResistances("ceiling")
+            r4 = osut.filmResistances("ceiling", tilt)
+            self.assertAlmostEqual(r1, 0.321, places=3)
+            self.assertAlmostEqual(r2, 0.321, places=3)
+            self.assertAlmostEqual(r3, 0.266, places=3)
+            self.assertAlmostEqual(r4, 0.266, places=3)
+
+            # Test adjacent ceilings.
+            ceiling = surface.adjacentSurface()
+            self.assertTrue(ceiling)
+            ceiling = ceiling.get()
+
+            nom = ceiling.nameString()
+            self.assertIn("_ceiling", nom)
+
+            # A horizontal ceiling faces upward, or 0°.
+            tilt = ceiling.tilt()
+            self.assertAlmostEqual(tilt, 0, places=4)
+
+            r1 = openstudio.model.PlanarSurface.stillAirFilmResistance(tilt) * 2
+            r2 = ceiling.filmResistance()
+            r3 = osut.filmResistances("ceiling")
+            r4 = osut.filmResistances("ceiling", tilt)
+            self.assertAlmostEqual(r1, 0.212, places=3) # not 0.321!
+            self.assertAlmostEqual(r2, 0.212, places=3) # not 0.321!
+            self.assertAlmostEqual(r3, 0.266, places=3) # same as floor above
+            self.assertAlmostEqual(r4, 0.266, places=3) # same as floor above
+
+            # OS-reported film resistances: 0.212 vs 0.321 - which one?
+            #
+            # ----------------------------------------------------------------------
+            # FYI, EnergyPlus reported (standard condition) U-factors:
+            #
+            #   - attic floors:
+            #       - U    with film: 0.151 (R    with film: 6.623)
+            #       - U without film: 0.158 (R without film: 6.329)
+            #     TOTAL film resistance = 0.267 ?
+            #
+            #   - adjacent ceilings below:
+            #       - U    with film: 0.151 (R    with film: 6.623)
+            #       - U without film: 0.158 (R without film: 6.329)
+            #     TOTAL film resistance = 0.267 !
+            #
+            # Regardless of how EnergyPlus determines combined film resistances,
+            # they are reported consistently, from either direction.
+            #
+            # Reminder:
+            #   fts["STILLAIR_HORIZONTALSURFACE_HEATFLOWSUPWARD"  ] = ~0.107
+            #   fts["STILLAIR_HORIZONTALSURFACE_HEATFLOWSDOWNWARD"] = ~0.162
+            #
+            # ... the sum of both = 0.269 (pretty close)
+            #
+            # Similarly:
+            #   OpenStudio::Model::PlanarSurface.stillAirFilmResistance(  0°) = 0.106
+            #   OpenStudio::Model::PlanarSurface.stillAirFilmResistance(180°) = 0.160
+            #
+            # ... the sum of both = 0.266 (even closer).
+
+        # Skylight well walls?
+        for surface in attic.surfaces():
+            if surface.surfaceType().lower() != "wall": continue
+
+            # Skylight well walls are vertical.
+            tilt = surface.tilt()
+            self.assertAlmostEqual(tilt, math.pi/2, places=4)
+            self.assertEqual(surface.outsideBoundaryCondition().lower(), "surface")
+
+            r1 = openstudio.model.PlanarSurface.stillAirFilmResistance(tilt) * 2
+            r2 = surface.filmResistance()
+            self.assertAlmostEqual(r1, 0.239, places=2)
+            self.assertAlmostEqual(r2, 0.239, places=2)
+
+            # Adjacent skylight well walls?
+            adjacent = surface.adjacentSurface()
+            self.assertTrue(adjacent)
+            adjacent = adjacent.get()
+
+            r1 = openstudio.model.PlanarSurface.stillAirFilmResistance(tilt) * 2
+            r2 = adjacent.filmResistance()
+            r3 = osut.filmResistances("partition")
+            r4 = osut.filmResistances("partition", tilt)
+            self.assertAlmostEqual(r1, 0.239, places=3)
+            self.assertAlmostEqual(r2, 0.239, places=3)
+            self.assertAlmostEqual(r3, 0.239, places=3)
+            self.assertAlmostEqual(r4, 0.239, places=3)
+
+        # Different from interzone walls in CONDITIONED, occupied spaces?
+        for space in model.getSpaces():
+            if space != attic: continue
+
+            for surface in space.surfaces():
+                if surface.surfaceType().lower() != "wall": continue
+                if surface.outsideBoundaryCondition().lower() != "surface": continue
+
+                tilt = surface.tilt()
+                self.assertAlmostEqual(tilt, math.pi/2, places=4)
+
+                r1 = openstudio.model.PlanarSurface.stillAirFilmResistance(tilt) * 2
+                r2 = surface.filmResistance()
+                r3 = osut.filmResistances("partition")
+                r4 = osut.filmResistances("partition", tilt)
+                self.assertAlmostEqual(r1, 0.239, places=3)
+                self.assertAlmostEqual(r2, 0.239, places=3)
+                self.assertAlmostEqual(r3, 0.239, places=3)
+                self.assertAlmostEqual(r4, 0.239, places=3)
+
+        # EnergyPlus reported film resistances for INTERZONE walls.
+        #   - insulated INTERZONE skylight well walls:
+        #     - U    with film: 0.292 (R    with film: 3.425)
+        #     - U without film: 0.314 (R without film: 3.185)
+        #   TOTAL film resistance = 0.240 (~same as OpenStudio)
+        #
+        # ... vs other INTERZONE walls:
+        #     - U    with film: 2.511 (R    with film: 0.398)
+        #     - U without film: 6.299 (R without film: 0.159)
+        #   TOTAL film resistance = 0.239 (same as OpenStudio)
+        # --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- #
+
+        # Repeat for plenum cases.
+        path  = openstudio.path("./tests/files/osms/out/seb2.osm")
+        model = translator.loadModel(path)
+        self.assertTrue(model)
+        model = model.get()
+
+        m0  = "osut.rsi"
+        m1 = "'lc' str? expecting LayeredConstruction (%s)" % m0
+        m2 = "'lc' NoneType? expecting LayeredConstruction (%s)" % m0
+        m3 = "Negative 'film' (%s)" % m0
+        m4 = "'film' NoneType? expecting float (%s)" % m0
+        m5 = "Negative 'temp K' (%s)" % m0
+        m6 = "'temp K' NoneType? expecting float (%s)" % m0
+
+        for s in model.getSurfaces():
+            if not s.isPartOfEnvelope(): continue
+
+            lc = s.construction()
+            self.assertTrue(lc)
+            lc = lc.get().to_LayeredConstruction()
+            self.assertTrue(lc)
+            lc = lc.get()
+            r1 = s.filmResistance()
+
+            if s.isPartOfEnvelope(): # i.e. outdoor-facing or ground-facing only
+                if s.isGroundSurface(): # 4x slabs on grade in SEB model
+                    r2 = osut.filmResistances("slab")
+                    r3 = osut.filmResistances("slab", s.tilt())
+                    self.assertAlmostEqual(r1, 0.160, places=3)
+                    self.assertAlmostEqual(r2, 0.162, places=3)
+                    self.assertAlmostEqual(r3, 0.160, places=3)
+                    self.assertAlmostEqual(osut.rsi(lc, r1), 0.448, places=3)
+                    self.assertAlmostEqual(osut.rsi(lc, r2), 0.450, places=3)
+                    self.assertAlmostEqual(osut.rsi(lc, r3), 0.448, places=3)
+                elif s.surfaceType().lower() == "wall":
+                    r2 = osut.filmResistances("wall")
+                    r3 = osut.filmResistances("wall", s.tilt())
+                    self.assertAlmostEqual(r1, 0.150, places=3)
+                    self.assertAlmostEqual(r2, 0.150, places=3)
+                    self.assertAlmostEqual(r3, 0.150, places=3)
+                    self.assertAlmostEqual(osut.rsi(lc, r1), 2.616, places=3)
+                    self.assertAlmostEqual(osut.rsi(lc, r2), 2.617, places=3)
+                    self.assertAlmostEqual(osut.rsi(lc, r3), 2.616, places=3)
+                else: # RoofCeiling
+                    self.assertEqual(s.surfaceType().lower(), "roofceiling")
+                    r2 = osut.filmResistances("roof")
+                    r3 = osut.filmResistances("roof", s.tilt())
+                    self.assertAlmostEqual(r1, 0.136, places=3)
+                    self.assertAlmostEqual(r2, 0.135, places=3)
+                    self.assertAlmostEqual(r3, 0.136, places=3)
+                    self.assertAlmostEqual(osut.rsi(lc, r1), 5.631, places=3)
+                    self.assertAlmostEqual(osut.rsi(lc, r2), 5.630, places=3)
+                    self.assertAlmostEqual(osut.rsi(lc, r3), 5.631, places=3)
+            else:
+                self.assertEqual(s.outsideBoundaryCondition().lower(), "surface")
+
+                if s.surfaceType().lower() == "wall":
+                    r2 = osut.filmResistances("wall")
+                    r3 = osut.filmResistances("wall", s.tilt())
+                    self.assertAlmostEqual(r1, 0.239, places=3)
+                    self.assertAlmostEqual(r2, 0.239, places=3)
+                    self.assertAlmostEqual(r3, 0.239, places=3)
+                    self.assertAlmostEqual(osut.rsi(lc, r1), 0.680, places=3)
+                    self.assertAlmostEqual(osut.rsi(lc, r2), 0.680, places=3)
+                    self.assertAlmostEqual(osut.rsi(lc, r3), 0.680, places=3)
+                elif s.surfaceType().lower() == "roofceiling":
+                    r2 = osut.filmResistances("ceiling")
+                    r3 = osut.filmResistances("ceiling", s.tilt())
+                    self.assertAlmostEqual(r1, 0.212, places=3) # attic ceiling
+                    self.assertAlmostEqual(r2, 0.266, places=3)
+                    self.assertAlmostEqual(r3, 0.266, places=3)
+                    self.assertAlmostEqual(osut.rsi(lc, r1), 0.331, places=3)
+                    self.assertAlmostEqual(osut.rsi(lc, r2), 0.386, places=3)
+                    self.assertAlmostEqual(osut.rsi(lc, r3), 0.386, places=3)
+                else:
+                    self.assertEqual(s.surfaceType().lower(), "floor")
+                    r2 = osut.filmResistances("ceiling")
+                    r3 = osut.filmResistances("ceiling", s.tilt())
+                    self.assertAlmostEqual(r1, 0.321, places=3) # attic floor
+                    self.assertAlmostEqual(r2, 0.266, places=3)
+                    self.assertAlmostEqual(r3, 0.266, places=3)
+                    self.assertAlmostEqual(osut.rsi(lc, r1), 0.440, places=3)
+                    self.assertAlmostEqual(osut.rsi(lc, r2), 0.386, places=3)
+                    self.assertAlmostEqual(osut.rsi(lc, r3), 0.386, places=3)
+
+        # Stress tests.
+        self.assertEqual(o.status(), 0)
+        self.assertAlmostEqual(osut.rsi("", 0.150), 0, places=2)
+        self.assertTrue(o.is_debug())
+        self.assertEqual(len(o.logs()), 1)
+        self.assertEqual(o.logs()[0]["message"], m1)
+        self.assertEqual(o.clean(), DBG)
+
+        self.assertAlmostEqual(osut.rsi(None, 0.150), 0, places=2)
+        self.assertTrue(o.is_debug())
+        self.assertEqual(len(o.logs()), 1)
+        self.assertEqual(o.logs()[0]["message"], m2)
+        self.assertEqual(o.clean(), DBG)
+
+        lc = model.getLayeredConstructionByName("SLAB-ON-GRADE-FLOOR")
+        self.assertTrue(lc)
+        lc = lc.get()
+
+        self.assertAlmostEqual(osut.rsi(lc, -1), 0, places=0)
+        self.assertTrue(o.is_error())
+        self.assertEqual(len(o.logs()), 1)
+        self.assertEqual(o.logs()[0]["message"], m3)
+        self.assertEqual(o.clean(), DBG)
+
+        self.assertAlmostEqual(osut.rsi(lc, None), 0, places=0)
+        self.assertTrue(o.is_debug())
+        self.assertEqual(len(o.logs()), 1)
+        self.assertEqual(o.logs()[0]["message"], m4)
+        self.assertEqual(o.clean(), DBG)
+
+        self.assertAlmostEqual(osut.rsi(lc, 0.150, -300), 0, places=0)
+        self.assertTrue(o.is_error())
+        self.assertEqual(len(o.logs()), 1)
+        self.assertEqual(o.logs()[0]["message"], m5)
+        self.assertEqual(o.clean(), DBG)
+
+        self.assertAlmostEqual(osut.rsi(lc, 0.150, None), 0, places=0)
+        self.assertTrue(o.is_debug())
+        self.assertEqual(len(o.logs()), 1)
+        self.assertEqual(o.logs()[0]["message"], m6)
+        self.assertEqual(o.clean(), DBG)
+
+        del model
+
     def test36_slab_generation(self):
         o = osut.oslg
         self.assertEqual(o.status(), 0)