For anyone running Windows 7, 8/8.1/10, this sudden space consumption can be as high as 6GB and it might be attributed to a folder called $WINDOWS.~BT that exists on your drive.

Microsoft is downloading Windows 10 to PCs, even if you don’t “reserve” a copy


What Is The $WINDOWS.~BT Folder On My Hard Drive?

Find the update called KB3035583 and uninstall it. You can now delete the $WINDOWS.~BT folder on your hard drive. You will need Admin privileges to do so but we’re assuming you already have those if you were able to uninstall the KB3035583 update. If you’re having trouble deleting the folder, try using disk clean up.