Async property in c#

I suggest you use asynchronous lazy initialization.

public static readonly AsyncLazy<StorageFolder> AppRootFolder =
    new AsyncLazy<StorageFolder>(() =>
    {
      return KnownFolders.DocumentsLibrary                    
          .CreateFolderAsync("theApp", CreationCollisionOption.OpenIfExists)
          .AsTask();
    });

You can then await it directly:

var rootFolder = await EnvironmentEx.AppRootFolder;

Good solution: Don't make a property. Make an async method.

"I hate await, how can I make everything synchronous?" solution: How to call asynchronous method from synchronous method in C#?

use the await keyword

 public async static StorageFolder GetAppRootFolder() 
 { 
          return await ApplicationData
                      .LocalFolder
                      .CreateFolderAsync("folderName");
 } 

and in your code

var myRootFolder = await StaticClass.GetAppRootFolder(); // this is a synchronous call as we are calling await immediately and will return the StorageFolder.