You do not need planning permission if you are not putting in any windows. However, you need to apply for Building Control consent.
If you want a dormer window or any type of window at the back and they wouldn't overlook footpaths or the public domain such as parks it doesn't need planning permission.
This is providing after doing the necessary calculations and drawings that the dormer window can not be seen above the roof crest from the highway.
Any windows at the front of the property overlooking the highway require planning permission.