diff --git a/src/harness/unittests/tsserverProjectSystem.ts b/src/harness/unittests/tsserverProjectSystem.ts
index 5ea0df91ca..356a7a8962 100644
--- a/src/harness/unittests/tsserverProjectSystem.ts
+++ b/src/harness/unittests/tsserverProjectSystem.ts
@@ -1007,6 +1007,41 @@ namespace ts.projectSystem {
             checkProjectRootFiles(projectService.configuredProjects[0], [commonFile1.path, commonFile2.path]);
         });
 
+        it("should disable features when the files are too large", () => {
+            const file1 = {
+                path: "/a/b/f1.js",
+                content: "let x =1;",
+                fileSize: 10 * 1024 * 1024
+            };
+            const file2 = {
+                path: "/a/b/f2.js",
+                content: "let y =1;",
+                fileSize: 6 * 1024 * 1024
+            };
+            const file3 = {
+                path: "/a/b/f3.js",
+                content: "let y =1;",
+                fileSize: 6 * 1024 * 1024
+            };
+
+            const proj1name = "proj1", proj2name = "proj2", proj3name = "proj3";
+
+            const host = createServerHost([file1, file2, file3]);
+            const projectService = createProjectService(host);
+
+            projectService.openExternalProject({ rootFiles: toExternalFiles([file1.path]), options: {}, projectFileName: proj1name });
+            const proj1 = projectService.findProject(proj1name);
+            assert.isTrue(proj1.languageServiceEnabled);
+
+            projectService.openExternalProject({ rootFiles: toExternalFiles([file2.path]), options: {}, projectFileName: proj2name });
+            const proj2 = projectService.findProject(proj2name);
+            assert.isTrue(proj2.languageServiceEnabled);
+
+            projectService.openExternalProject({ rootFiles: toExternalFiles([file3.path]), options: {}, projectFileName: proj3name });
+            const proj3 = projectService.findProject(proj3name);
+            assert.isFalse(proj3.languageServiceEnabled);
+        });
+
         it("should use only one inferred project if 'useOneInferredProject' is set", () => {
             const file1 = {
                 path: "/a/b/main.ts",
diff --git a/src/server/editorServices.ts b/src/server/editorServices.ts
index 397de9ead3..8af6fe5d34 100644
--- a/src/server/editorServices.ts
+++ b/src/server/editorServices.ts
@@ -254,6 +254,7 @@ namespace ts.server {
 
         private compilerOptionsForInferredProjects: CompilerOptions;
         private compileOnSaveForInferredProjects: boolean;
+        private readonly projectToSizeMap: Map<number> = createMap<number>();
         private readonly directoryWatchers: DirectoryWatchers;
         private readonly throttledOperations: ThrottledOperations;
 
@@ -563,9 +564,11 @@ namespace ts.server {
             switch (project.projectKind) {
                 case ProjectKind.External:
                     removeItemFromSet(this.externalProjects, <ExternalProject>project);
+                    this.projectToSizeMap.delete((project as ExternalProject).externalProjectName);
                     break;
                 case ProjectKind.Configured:
                     removeItemFromSet(this.configuredProjects, <ConfiguredProject>project);
+                    this.projectToSizeMap.delete((project as ConfiguredProject).canonicalConfigFilePath);
                     break;
                 case ProjectKind.Inferred:
                     removeItemFromSet(this.inferredProjects, <InferredProject>project);
@@ -852,10 +855,15 @@ namespace ts.server {
             return { success: true, projectOptions, configFileErrors: errors };
         }
 
-        private exceededTotalSizeLimitForNonTsFiles<T>(options: CompilerOptions, fileNames: T[], propertyReader: FilePropertyReader<T>) {
+        private exceededTotalSizeLimitForNonTsFiles<T>(name: string, options: CompilerOptions, fileNames: T[], propertyReader: FilePropertyReader<T>) {
             if (options && options.disableSizeLimit || !this.host.getFileSize) {
                 return false;
             }
+
+            let availableSpace = maxProgramSizeForNonTsFiles;
+            this.projectToSizeMap.set(name, 0);
+            this.projectToSizeMap.forEach(val => (availableSpace -= (val || 0)));
+
             let totalNonTsFileSize = 0;
             for (const f of fileNames) {
                 const fileName = propertyReader.getFileName(f);
@@ -864,9 +872,16 @@ namespace ts.server {
                 }
                 totalNonTsFileSize += this.host.getFileSize(fileName);
                 if (totalNonTsFileSize > maxProgramSizeForNonTsFiles) {
+                    // Keep the size as zero since it's disabled
                     return true;
                 }
             }
+
+            if (totalNonTsFileSize > availableSpace) {
+                return true;
+            }
+
+            this.projectToSizeMap.set(name, totalNonTsFileSize);
             return false;
         }
 
@@ -877,7 +892,7 @@ namespace ts.server {
                 this,
                 this.documentRegistry,
                 compilerOptions,
-                /*languageServiceEnabled*/ !this.exceededTotalSizeLimitForNonTsFiles(compilerOptions, files, externalFilePropertyReader),
+                /*languageServiceEnabled*/ !this.exceededTotalSizeLimitForNonTsFiles(projectFileName, compilerOptions, files, externalFilePropertyReader),
                 options.compileOnSave === undefined ? true : options.compileOnSave);
 
             this.addFilesToProjectAndUpdateGraph(project, files, externalFilePropertyReader, /*clientFileName*/ undefined, typeAcquisition, /*configFileErrors*/ undefined);
@@ -897,7 +912,7 @@ namespace ts.server {
         }
 
         private createAndAddConfiguredProject(configFileName: NormalizedPath, projectOptions: ProjectOptions, configFileErrors: Diagnostic[], clientFileName?: string) {
-            const sizeLimitExceeded = this.exceededTotalSizeLimitForNonTsFiles(projectOptions.compilerOptions, projectOptions.files, fileNamePropertyReader);
+            const sizeLimitExceeded = this.exceededTotalSizeLimitForNonTsFiles(configFileName, projectOptions.compilerOptions, projectOptions.files, fileNamePropertyReader);
             const project = new ConfiguredProject(
                 configFileName,
                 this,
@@ -1050,7 +1065,7 @@ namespace ts.server {
                 return configFileErrors;
             }
 
-            if (this.exceededTotalSizeLimitForNonTsFiles(projectOptions.compilerOptions, projectOptions.files, fileNamePropertyReader)) {
+            if (this.exceededTotalSizeLimitForNonTsFiles(project.canonicalConfigFilePath, projectOptions.compilerOptions, projectOptions.files, fileNamePropertyReader)) {
                 project.setCompilerOptions(projectOptions.compilerOptions);
                 if (!project.languageServiceEnabled) {
                     // language service is already disabled
@@ -1414,7 +1429,7 @@ namespace ts.server {
             if (externalProject) {
                 if (!tsConfigFiles) {
                     const compilerOptions = convertCompilerOptions(proj.options);
-                    if (this.exceededTotalSizeLimitForNonTsFiles(compilerOptions, proj.rootFiles, externalFilePropertyReader)) {
+                    if (this.exceededTotalSizeLimitForNonTsFiles(proj.projectFileName, compilerOptions, proj.rootFiles, externalFilePropertyReader)) {
                         externalProject.disableLanguageService();
                     }
                     else {
diff --git a/src/server/project.ts b/src/server/project.ts
index 385816b102..e57e605d65 100644
--- a/src/server/project.ts
+++ b/src/server/project.ts
@@ -1031,7 +1031,7 @@ namespace ts.server {
 
     export class ExternalProject extends Project {
         private typeAcquisition: TypeAcquisition;
-        constructor(externalProjectName: string,
+        constructor(public externalProjectName: string,
             projectService: ProjectService,
             documentRegistry: ts.DocumentRegistry,
             compilerOptions: CompilerOptions,
diff --git a/src/server/session.ts b/src/server/session.ts
index 8dd0411d07..11c99dfe46 100644
--- a/src/server/session.ts
+++ b/src/server/session.ts
@@ -25,8 +25,14 @@ namespace ts.server {
         return ((1e9 * seconds) + nanoseconds) / 1000000.0;
     }
 
-    function shouldSkipSematicCheck(project: Project) {
-        return (project.projectKind === ProjectKind.Inferred || project.projectKind === ProjectKind.External) && project.isJsOnlyProject();
+    function shouldSkipSemanticCheck(project: Project) {
+        if (project.projectKind === ProjectKind.Inferred || project.projectKind === ProjectKind.External) {
+            return project.isJsOnlyProject();
+        }
+        else {
+            // For configured projects, require that skipLibCheck be set also
+            return project.getCompilerOptions().skipLibCheck && project.isJsOnlyProject();
+        }
     }
 
     interface FileStart {
@@ -447,7 +453,7 @@ namespace ts.server {
         private semanticCheck(file: NormalizedPath, project: Project) {
             try {
                 let diags: Diagnostic[] = [];
-                if (!shouldSkipSematicCheck(project)) {
+                if (!shouldSkipSemanticCheck(project)) {
                     diags = project.getLanguageService().getSemanticDiagnostics(file);
                 }
 
@@ -555,7 +561,7 @@ namespace ts.server {
 
         private getDiagnosticsWorker(args: protocol.FileRequestArgs, isSemantic: boolean, selector: (project: Project, file: string) => Diagnostic[], includeLinePosition: boolean) {
             const { project, file } = this.getFileAndProject(args);
-            if (isSemantic && shouldSkipSematicCheck(project)) {
+            if (isSemantic && shouldSkipSemanticCheck(project)) {
                 return [];
             }
             const scriptInfo = project.getScriptInfoForNormalizedPath(file);