diff --git a/src/EnergyPlus/DataHeatBalance.hh b/src/EnergyPlus/DataHeatBalance.hh
index be984eb2def..afad46866c3 100644
--- a/src/EnergyPlus/DataHeatBalance.hh
+++ b/src/EnergyPlus/DataHeatBalance.hh
@@ -458,6 +458,7 @@ namespace DataHeatBalance {
         Real64 Volume = Constant::AutoCalculate;        // Volume entered by user [m3] or calculated
         Real64 ExtGrossWallArea = 0.0;                  // Exterior Wall Area for Zone (Gross)
         Real64 ExteriorTotalSurfArea = 0.0;             // Total surface area of all exterior surfaces for Zone
+        Real64 extPerimeter = 0.0;                      // Total exposed perimeter (sum of width of exterior walls)
         int SystemZoneNodeNumber = 0;                   // This is the zone or space node number for the system for a controlled zone
         Real64 FloorArea = 0.0;                         // Floor area used for this space
         Real64 TotOccupants = 0.0;                      // total design occupancy (sum of NumberOfPeople for the space People objects, not multiplied)
diff --git a/src/EnergyPlus/DataZoneEquipment.cc b/src/EnergyPlus/DataZoneEquipment.cc
index 869dfd51857..488102e47a3 100644
--- a/src/EnergyPlus/DataZoneEquipment.cc
+++ b/src/EnergyPlus/DataZoneEquipment.cc
@@ -1867,11 +1867,9 @@ void ZoneEquipmentSplitterMixer::size(EnergyPlusData &state)
         }
         break;
     case DataZoneEquipment::SpaceEquipSizingBasis::PerimeterLength:
-        ShowFatalError(state,
-                       format("ZoneEquipmentSplitterMixer::size: Space Fraction Method={} not supported for {}={}",
-                              DataZoneEquipment::spaceEquipSizingBasisNamesUC[(int)this->spaceSizingBasis],
-                              BranchNodeConnections::ConnectionObjectTypeNames[(int)this->spaceEquipType],
-                              this->Name));
+        for (auto &thisSpace : this->spaces) {
+            spacesTotal += state.dataHeatBal->space(thisSpace.spaceIndex).extPerimeter;
+        }
         break;
     default:
         // If method is not set, then return
@@ -1890,43 +1888,41 @@ void ZoneEquipmentSplitterMixer::size(EnergyPlusData &state)
         for (auto &thisSpace : this->spaces) {
             thisSpace.fraction = spaceFrac;
         }
-        return;
+    } else {
+        // Calculate space fractions
+        for (auto &thisSpace : this->spaces) {
+            if (thisSpace.fraction == DataSizing::AutoSize) {
+                switch (this->spaceSizingBasis) {
+                case DataZoneEquipment::SpaceEquipSizingBasis::DesignCoolingLoad:
+                    thisSpace.fraction = state.dataSize->FinalSpaceSizing(thisSpace.spaceIndex).DesCoolLoad / spacesTotal;
+                    break;
+                case DataZoneEquipment::SpaceEquipSizingBasis::DesignHeatingLoad:
+                    thisSpace.fraction = state.dataSize->FinalSpaceSizing(thisSpace.spaceIndex).DesHeatLoad / spacesTotal;
+                    break;
+                case DataZoneEquipment::SpaceEquipSizingBasis::FloorArea:
+                    thisSpace.fraction = state.dataHeatBal->space(thisSpace.spaceIndex).FloorArea / spacesTotal;
+                    break;
+                case DataZoneEquipment::SpaceEquipSizingBasis::Volume:
+                    thisSpace.fraction = state.dataHeatBal->space(thisSpace.spaceIndex).Volume / spacesTotal;
+                    break;
+                case DataZoneEquipment::SpaceEquipSizingBasis::PerimeterLength:
+                    thisSpace.fraction = state.dataHeatBal->space(thisSpace.spaceIndex).extPerimeter / spacesTotal;
+                    break;
+                default:
+                    break;
+                }
+            }
+        }
     }
-
-    // Calculate space fractions
+    // Report sizing results
     int spaceCounter = 0;
     for (auto &thisSpace : this->spaces) {
         ++spaceCounter;
-        if (thisSpace.fraction == DataSizing::AutoSize) {
-            switch (this->spaceSizingBasis) {
-            case DataZoneEquipment::SpaceEquipSizingBasis::DesignCoolingLoad:
-                thisSpace.fraction = state.dataSize->FinalSpaceSizing(thisSpace.spaceIndex).DesCoolLoad / spacesTotal;
-                break;
-            case DataZoneEquipment::SpaceEquipSizingBasis::DesignHeatingLoad:
-                thisSpace.fraction = state.dataSize->FinalSpaceSizing(thisSpace.spaceIndex).DesHeatLoad / spacesTotal;
-                break;
-            case DataZoneEquipment::SpaceEquipSizingBasis::FloorArea:
-                thisSpace.fraction = state.dataHeatBal->space(thisSpace.spaceIndex).FloorArea / spacesTotal;
-                break;
-            case DataZoneEquipment::SpaceEquipSizingBasis::Volume:
-                thisSpace.fraction = state.dataHeatBal->space(thisSpace.spaceIndex).Volume / spacesTotal;
-                break;
-            case DataZoneEquipment::SpaceEquipSizingBasis::PerimeterLength:
-                ShowFatalError(state,
-                               format("ZoneEquipmentSplitterMixer::size: Space Fraction Method={} not supported for {}={}",
-                                      DataZoneEquipment::spaceEquipSizingBasisNamesUC[(int)this->spaceSizingBasis],
-                                      BranchNodeConnections::ConnectionObjectTypeNames[(int)this->spaceEquipType],
-                                      this->Name));
-                break;
-            default:
-                break;
-            }
-            BaseSizer::reportSizerOutput(state,
-                                         BranchNodeConnections::ConnectionObjectTypeNames[(int)this->spaceEquipType],
-                                         this->Name,
-                                         format("Space {} Fraction", spaceCounter),
-                                         thisSpace.fraction);
-        }
+        BaseSizer::reportSizerOutput(state,
+                                     BranchNodeConnections::ConnectionObjectTypeNames[(int)this->spaceEquipType],
+                                     this->Name,
+                                     format("Space {} Fraction", spaceCounter),
+                                     thisSpace.fraction);
     }
 }
 
diff --git a/src/EnergyPlus/SurfaceGeometry.cc b/src/EnergyPlus/SurfaceGeometry.cc
index 5e04b458335..a51d937e5f4 100644
--- a/src/EnergyPlus/SurfaceGeometry.cc
+++ b/src/EnergyPlus/SurfaceGeometry.cc
@@ -423,6 +423,8 @@ namespace SurfaceGeometry {
                         thisZone.ExtGrossWallArea += thisSurface.GrossArea;
                         thisSpace.ExtGrossWallArea += thisSurface.GrossArea;
                         thisZone.ExtGrossWallArea_Multiplied += thisSurface.GrossArea * thisZone.Multiplier * thisZone.ListMultiplier;
+                        thisZone.extPerimeter += thisSurface.Width;
+                        thisSpace.extPerimeter += thisSurface.Width;
                         if (DetailedWWR) {
                             print(state.files.debug,
                                   "{},Wall,{:.2R},{:.1R}\n",