diff --git a/Source/Scene/Cesium3DTile.js b/Source/Scene/Cesium3DTile.js
index 63a86c6655e3..6d4354c53cbc 100644
--- a/Source/Scene/Cesium3DTile.js
+++ b/Source/Scene/Cesium3DTile.js
@@ -96,13 +96,20 @@ define([
          */
         this.geometricError = header.geometricError;
 
-// TODO: use default for a smaller tree.json?  Or inherit from parent.  Same for "type" and others.
+        var refine;
+        if (defined(header.refine)) {
+            refine = (header.refine === 'replace') ? Cesium3DTileRefine.REPLACE : Cesium3DTileRefine.ADD;
+        } else if (defined(parent)) {
+            // Inherit from parent tile if omitted.
+            refine = parent.refine;
+        }
+
         /**
          * DOC_TBA
          *
          * @readonly
          */
-        this.refine = (header.refine === 'replace') ? Cesium3DTileRefine.REPLACE : Cesium3DTileRefine.ADD;
+        this.refine = refine;
 
         /**
          * DOC_TBA
diff --git a/Specs/Data/Cesium3DTiles/Batched/BatchedNoBuildings/tiles.json b/Specs/Data/Cesium3DTiles/Batched/BatchedNoBuildings/tiles.json
index d9aeed2d8455..10b2438cc0ef 100644
--- a/Specs/Data/Cesium3DTiles/Batched/BatchedNoBuildings/tiles.json
+++ b/Specs/Data/Cesium3DTiles/Batched/BatchedNoBuildings/tiles.json
@@ -18,6 +18,7 @@
             ]
         },
         "geometricError": 0,
+        "refine": "add",
         "content": {
             "url": "batchedNoBuildings.b3dm"
         }
diff --git a/Specs/Data/Cesium3DTiles/Batched/BatchedWithBatchTable/tiles.json b/Specs/Data/Cesium3DTiles/Batched/BatchedWithBatchTable/tiles.json
index 3988f0e4cf57..fbfd0c3c30a6 100644
--- a/Specs/Data/Cesium3DTiles/Batched/BatchedWithBatchTable/tiles.json
+++ b/Specs/Data/Cesium3DTiles/Batched/BatchedWithBatchTable/tiles.json
@@ -18,6 +18,7 @@
             ]
         },
         "geometricError": 0,
+        "refine": "add",
         "content": {
             "url": "batchedWithBatchTable.b3dm"
         }
diff --git a/Specs/Data/Cesium3DTiles/Batched/BatchedWithoutBatchTable/tiles.json b/Specs/Data/Cesium3DTiles/Batched/BatchedWithoutBatchTable/tiles.json
index 75c6b9705672..b53af38b2f34 100644
--- a/Specs/Data/Cesium3DTiles/Batched/BatchedWithoutBatchTable/tiles.json
+++ b/Specs/Data/Cesium3DTiles/Batched/BatchedWithoutBatchTable/tiles.json
@@ -18,6 +18,7 @@
             ]
         },
         "geometricError": 0,
+        "refine": "add",
         "content": {
             "url": "batchedWithoutBatchTable.b3dm"
         }
diff --git a/Specs/Data/Cesium3DTiles/Composite/Composite/tiles.json b/Specs/Data/Cesium3DTiles/Composite/Composite/tiles.json
index 06af37b1acca..168e9cdeb172 100644
--- a/Specs/Data/Cesium3DTiles/Composite/Composite/tiles.json
+++ b/Specs/Data/Cesium3DTiles/Composite/Composite/tiles.json
@@ -18,6 +18,7 @@
             ]
         },
         "geometricError": 0,
+        "refine": "add",
         "content": {
             "url": "composite.cmpt"
         }
diff --git a/Specs/Data/Cesium3DTiles/Composite/CompositeOfComposite/tiles.json b/Specs/Data/Cesium3DTiles/Composite/CompositeOfComposite/tiles.json
index c0071515616e..af33227b6908 100644
--- a/Specs/Data/Cesium3DTiles/Composite/CompositeOfComposite/tiles.json
+++ b/Specs/Data/Cesium3DTiles/Composite/CompositeOfComposite/tiles.json
@@ -18,6 +18,7 @@
             ]
         },
         "geometricError": 0,
+        "refine": "add",
         "content": {
             "url": "compositeOfComposite.cmpt"
         }
diff --git a/Specs/Data/Cesium3DTiles/Instanced/InstancedGltfEmbedded/tiles.json b/Specs/Data/Cesium3DTiles/Instanced/InstancedGltfEmbedded/tiles.json
index 7c4d0c245d82..d6622665c9e6 100644
--- a/Specs/Data/Cesium3DTiles/Instanced/InstancedGltfEmbedded/tiles.json
+++ b/Specs/Data/Cesium3DTiles/Instanced/InstancedGltfEmbedded/tiles.json
@@ -18,6 +18,7 @@
             ]
         },
         "geometricError": 0,
+        "refine": "add",
         "content": {
             "url": "instancedGltfEmbedded.i3dm"
         }
diff --git a/Specs/Data/Cesium3DTiles/Instanced/InstancedGltfExternal/tiles.json b/Specs/Data/Cesium3DTiles/Instanced/InstancedGltfExternal/tiles.json
index 43424af21847..7136029e8f02 100644
--- a/Specs/Data/Cesium3DTiles/Instanced/InstancedGltfExternal/tiles.json
+++ b/Specs/Data/Cesium3DTiles/Instanced/InstancedGltfExternal/tiles.json
@@ -18,6 +18,7 @@
             ]
         },
         "geometricError": 0,
+        "refine": "add",
         "content": {
             "url": "instancedGltfExternal.i3dm"
         }
diff --git a/Specs/Data/Cesium3DTiles/Instanced/InstancedWithBatchTable/tiles.json b/Specs/Data/Cesium3DTiles/Instanced/InstancedWithBatchTable/tiles.json
index cccc0f411b04..12a0d3e773e6 100644
--- a/Specs/Data/Cesium3DTiles/Instanced/InstancedWithBatchTable/tiles.json
+++ b/Specs/Data/Cesium3DTiles/Instanced/InstancedWithBatchTable/tiles.json
@@ -18,6 +18,7 @@
             ]
         },
         "geometricError": 0,
+        "refine": "add",
         "content": {
             "url": "instancedWithBatchTable.i3dm"
         }
diff --git a/Specs/Data/Cesium3DTiles/Instanced/InstancedWithoutBatchTable/tiles.json b/Specs/Data/Cesium3DTiles/Instanced/InstancedWithoutBatchTable/tiles.json
index 08efcbc2e2df..e5a1b1c09725 100644
--- a/Specs/Data/Cesium3DTiles/Instanced/InstancedWithoutBatchTable/tiles.json
+++ b/Specs/Data/Cesium3DTiles/Instanced/InstancedWithoutBatchTable/tiles.json
@@ -18,6 +18,7 @@
             ]
         },
         "geometricError": 0,
+        "refine": "add",
         "content": {
             "url": "instancedWithoutBatchTable.i3dm"
         }
diff --git a/Specs/Data/Cesium3DTiles/Points/Points/tiles.json b/Specs/Data/Cesium3DTiles/Points/Points/tiles.json
index bd282b98ab0d..91d7aaa4c6cb 100644
--- a/Specs/Data/Cesium3DTiles/Points/Points/tiles.json
+++ b/Specs/Data/Cesium3DTiles/Points/Points/tiles.json
@@ -10,6 +10,7 @@
             ]
         },
         "geometricError": 0,
+        "refine": "add",
         "content": {
             "url": "points.pnts"
         }
diff --git a/Specs/Data/Cesium3DTiles/Tilesets/Tileset/tiles.json b/Specs/Data/Cesium3DTiles/Tilesets/Tileset/tiles.json
index 3b352b2e2a6d..222e1dcd4b4a 100644
--- a/Specs/Data/Cesium3DTiles/Tilesets/Tileset/tiles.json
+++ b/Specs/Data/Cesium3DTiles/Tilesets/Tileset/tiles.json
@@ -18,6 +18,7 @@
             ]
         },
         "geometricError": 70,
+        "refine": "add",
         "content": {
             "url": "parent.b3dm",
             "boundingVolume": {
diff --git a/Specs/Data/Cesium3DTiles/Tilesets/TilesetEmptyRoot/tiles.json b/Specs/Data/Cesium3DTiles/Tilesets/TilesetEmptyRoot/tiles.json
index 2b29564e42e7..b41163bc9028 100644
--- a/Specs/Data/Cesium3DTiles/Tilesets/TilesetEmptyRoot/tiles.json
+++ b/Specs/Data/Cesium3DTiles/Tilesets/TilesetEmptyRoot/tiles.json
@@ -18,6 +18,7 @@
             ]
         },
         "geometricError": 70,
+        "refine": "add",
         "children": [
             {
                 "boundingVolume": {
diff --git a/Specs/Data/Cesium3DTiles/Tilesets/TilesetInvalid/tiles.json b/Specs/Data/Cesium3DTiles/Tilesets/TilesetInvalid/tiles.json
index 5e0f733edf22..392a82b9610d 100644
--- a/Specs/Data/Cesium3DTiles/Tilesets/TilesetInvalid/tiles.json
+++ b/Specs/Data/Cesium3DTiles/Tilesets/TilesetInvalid/tiles.json
@@ -18,6 +18,7 @@
             ]
         },
         "geometricError": 70,
+        "refine": "add",
         "content": {
             "url": "parent.b3dm",
             "boundingVolume": {
diff --git a/Specs/Data/Cesium3DTiles/Tilesets/TilesetOfTilesets/tiles.json b/Specs/Data/Cesium3DTiles/Tilesets/TilesetOfTilesets/tiles.json
index f6301c510800..cb6a75a86608 100644
--- a/Specs/Data/Cesium3DTiles/Tilesets/TilesetOfTilesets/tiles.json
+++ b/Specs/Data/Cesium3DTiles/Tilesets/TilesetOfTilesets/tiles.json
@@ -18,6 +18,7 @@
             ]
         },
         "geometricError": 70,
+        "refine": "add",
         "content": {
             "url": "tiles2.json"
         }
diff --git a/Specs/Data/Cesium3DTiles/Tilesets/TilesetOfTilesets/tiles2.json b/Specs/Data/Cesium3DTiles/Tilesets/TilesetOfTilesets/tiles2.json
index edeecd1805ed..d91ad33c7cc3 100644
--- a/Specs/Data/Cesium3DTiles/Tilesets/TilesetOfTilesets/tiles2.json
+++ b/Specs/Data/Cesium3DTiles/Tilesets/TilesetOfTilesets/tiles2.json
@@ -27,6 +27,7 @@
                     ]
                 },
                 "geometricError": 0,
+                "refine": "add",
                 "content": {
                     "url": "tiles3.json"
                 }
diff --git a/Specs/Data/Cesium3DTiles/Tilesets/TilesetOfTilesets/tiles3.json b/Specs/Data/Cesium3DTiles/Tilesets/TilesetOfTilesets/tiles3.json
index a84b36efb13d..c935ef99d55b 100644
--- a/Specs/Data/Cesium3DTiles/Tilesets/TilesetOfTilesets/tiles3.json
+++ b/Specs/Data/Cesium3DTiles/Tilesets/TilesetOfTilesets/tiles3.json
@@ -11,6 +11,7 @@
             ]
         },
         "geometricError": 0,
+        "refine": "add",
         "content": {
             "url": "ll.b3dm"
         }
diff --git a/Specs/Data/Cesium3DTiles/Tilesets/TilesetReplacement1/tiles.json b/Specs/Data/Cesium3DTiles/Tilesets/TilesetReplacement1/tiles.json
index a35c2df3ee54..e94b4b703c68 100644
--- a/Specs/Data/Cesium3DTiles/Tilesets/TilesetReplacement1/tiles.json
+++ b/Specs/Data/Cesium3DTiles/Tilesets/TilesetReplacement1/tiles.json
@@ -46,6 +46,7 @@
                     ]
                 },
                 "geometricError": 70,
+                "refine": "add",
                 "children": [
                     {
                         "boundingVolume": {
@@ -93,6 +94,7 @@
                     ]
                 },
                 "geometricError": 70,
+                "refine": "add",
                 "children": [
                     {
                         "boundingVolume": {
diff --git a/Specs/Data/Cesium3DTiles/Tilesets/TilesetReplacement2/tiles.json b/Specs/Data/Cesium3DTiles/Tilesets/TilesetReplacement2/tiles.json
index 2c95941685a4..69d30fc1f54a 100644
--- a/Specs/Data/Cesium3DTiles/Tilesets/TilesetReplacement2/tiles.json
+++ b/Specs/Data/Cesium3DTiles/Tilesets/TilesetReplacement2/tiles.json
@@ -6,6 +6,7 @@
         }
     },
     "geometricError": 240,
+    "refine": "add",
     "root": {
         "boundingVolume": {
             "region": [