diff --git a/schemas/discriminated.json b/schemas/discriminated.json
new file mode 100644
index 00000000..29649659
--- /dev/null
+++ b/schemas/discriminated.json
@@ -0,0 +1,159 @@
+{
+  "$id": "@next",
+  "$schema": "http://json-schema.org/draft-07/schema#",
+  "anyOf": [
+    {
+      "$ref": "#/definitions/PlanningPermissionApplication"
+    },
+    {
+      "$ref": "#/definitions/PriorApprovalApplication"
+    },
+    {
+      "$ref": "#/definitions/WorksToTreesApplication"
+    }
+  ],
+  "definitions": {
+    "PPUser": {
+      "additionalProperties": false,
+      "properties": {
+        "ppSpecificProperty": {
+          "type": "boolean"
+        },
+        "role": {
+          "enum": [
+            "applicant",
+            "agent",
+            "proxy"
+          ],
+          "type": "string"
+        }
+      },
+      "required": [
+        "ppSpecificProperty",
+        "role"
+      ],
+      "type": "object"
+    },
+    "PlanningPermissionApplication": {
+      "additionalProperties": false,
+      "description": "Application for a \"Planning Permission\" project",
+      "properties": {
+        "data": {
+          "additionalProperties": false,
+          "properties": {
+            "user": {
+              "$ref": "#/definitions/PPUser"
+            }
+          },
+          "required": [
+            "user"
+          ],
+          "type": "object"
+        },
+        "primaryApplicationType": {
+          "const": "pp",
+          "type": "string"
+        }
+      },
+      "required": [
+        "primaryApplicationType",
+        "data"
+      ],
+      "type": "object"
+    },
+    "PriorApprovalApplication": {
+      "additionalProperties": false,
+      "description": "Application for a \"Prior Approval\" project",
+      "properties": {
+        "data": {
+          "additionalProperties": false,
+          "properties": {
+            "user": {
+              "$ref": "#/definitions/UserBase"
+            }
+          },
+          "required": [
+            "user"
+          ],
+          "type": "object"
+        },
+        "primaryApplicationType": {
+          "const": "pa",
+          "type": "string"
+        }
+      },
+      "required": [
+        "primaryApplicationType",
+        "data"
+      ],
+      "type": "object"
+    },
+    "UserBase": {
+      "additionalProperties": false,
+      "properties": {
+        "role": {
+          "enum": [
+            "applicant",
+            "agent",
+            "proxy"
+          ],
+          "type": "string"
+        }
+      },
+      "required": [
+        "role"
+      ],
+      "type": "object"
+    },
+    "WTTUser": {
+      "additionalProperties": false,
+      "properties": {
+        "role": {
+          "enum": [
+            "applicant",
+            "agent",
+            "proxy"
+          ],
+          "type": "string"
+        },
+        "wttSpecificProperty": {
+          "type": "boolean"
+        }
+      },
+      "required": [
+        "role",
+        "wttSpecificProperty"
+      ],
+      "type": "object"
+    },
+    "WorksToTreesApplication": {
+      "additionalProperties": false,
+      "description": "Application for a \"Works to trees\" project",
+      "properties": {
+        "data": {
+          "additionalProperties": false,
+          "properties": {
+            "user": {
+              "$ref": "#/definitions/WTTUser"
+            }
+          },
+          "required": [
+            "user"
+          ],
+          "type": "object"
+        },
+        "primaryApplicationType": {
+          "const": "wtt",
+          "type": "string"
+        }
+      },
+      "required": [
+        "primaryApplicationType",
+        "data"
+      ],
+      "type": "object"
+    }
+  },
+  "description": "The root specification for a planning application in England generated by a digital planning service",
+  "title": "App"
+}
\ No newline at end of file
diff --git a/scripts/build-schema.sh b/scripts/build-schema.sh
index 7eee9132..0b7dd37a 100755
--- a/scripts/build-schema.sh
+++ b/scripts/build-schema.sh
@@ -7,8 +7,8 @@ version="${VERSION:-@next}"
 
 echo "Version set to $version"
 
-dirs=("digitalPlanningApplication")
-types=("DigitalPlanningApplication")
+dirs=("digitalPlanningApplication" "discriminated")
+types=("DigitalPlanningApplication" "App")
 
 for i in "${!dirs[@]}"; do
   dir=${dirs[$i]}
diff --git a/types/schemas/digitalPlanningApplication/enums/ApplicationTypes.ts b/types/schemas/digitalPlanningApplication/enums/ApplicationTypes.ts
index b9d516de..40bc0d7c 100644
--- a/types/schemas/digitalPlanningApplication/enums/ApplicationTypes.ts
+++ b/types/schemas/digitalPlanningApplication/enums/ApplicationTypes.ts
@@ -180,6 +180,10 @@ type GenericApplicationType<TKey extends ApplicationTypeKeys> = {
   description: (typeof ApplicationTypes)[TKey];
 };
 
+type ExtractPrimaryKeys<T> = T extends `${infer K}.${string}` ? K : T;
+
+export type PrimaryApplicationTypes = ExtractPrimaryKeys<ApplicationTypeKeys>;
+
 type ApplicationTypeMap = {
   [K in ApplicationTypeKeys]: GenericApplicationType<K>;
 };
diff --git a/types/schemas/discriminated/User.ts b/types/schemas/discriminated/User.ts
new file mode 100644
index 00000000..09afce99
--- /dev/null
+++ b/types/schemas/discriminated/User.ts
@@ -0,0 +1,30 @@
+import {PrimaryApplicationTypes} from '../digitalPlanningApplication/enums/ApplicationTypes';
+
+export interface UserBase {
+  role: 'applicant' | 'agent' | 'proxy';
+}
+
+export interface WTTUser extends UserBase {
+  wttSpecificProperty: boolean;
+}
+
+export interface PPUser extends UserBase {
+  ppSpecificProperty: boolean;
+}
+
+/**
+ * @internal
+ */
+interface UserVariants {
+  wtt: WTTUser;
+  pp: PPUser;
+}
+
+/**
+ * @internal
+ */
+export type User<T extends PrimaryApplicationTypes> =
+  T extends keyof UserVariants
+    ? UserVariants[T]
+    : // Default value for non-specific application types
+      UserBase;
diff --git a/types/schemas/discriminated/index.ts b/types/schemas/discriminated/index.ts
new file mode 100644
index 00000000..580f77b9
--- /dev/null
+++ b/types/schemas/discriminated/index.ts
@@ -0,0 +1,33 @@
+import {PrimaryApplicationTypes} from '../digitalPlanningApplication/enums/ApplicationTypes';
+import {User} from './User';
+
+interface GenericApplication<T extends PrimaryApplicationTypes> {
+  primaryApplicationType: T;
+  data: {
+    user: User<T>;
+  };
+}
+
+/**
+ * @description Application for a "Planning Permission" project
+ */
+export type PlanningPermissionApplication = GenericApplication<'pp'>;
+
+/**
+ * @description Application for a "Prior Approval" project
+ */
+export type PriorApprovalApplication = GenericApplication<'pa'>;
+
+/**
+ * @description Application for a "Works to trees" project
+ */
+export type WorksToTreesApplication = GenericApplication<'wtt'>;
+
+/**
+ * @title App
+ * @description The root specification for a planning application in England generated by a digital planning service
+ */
+export type App =
+  | PlanningPermissionApplication
+  | PriorApprovalApplication
+  | WorksToTreesApplication;