Replacing garage doors with timber wall

[Loofah]

I have an separate garage, brick build with two wooden doors that open outward. They don;t fit all that well anymore and the timber frame is rotting in places.
As I can't use it as a garage I've decided to remove the doors and rotten frame and replace with a timber stud wall with a window and finish off with cladding.
I have a couple of questions; firstly is there any reason I wouldn't be allowed to do this due to planning or other reason? Secondly, what should be the required separation between uprights and noggins? 600mm?

EDIT: Also, do I need to add a header above the window frame or could that just be screwed into the wooden lintel above it?

 

[foxhole]

Quick call to local council planning will answer question 1 , will this amount to a change in use?

 

[Loofah]

Not at all, just a way of stopping the leaky doors and rotting frame. I can't see any reason why I shouldn't be allowed but wondered if anyone here has experienced it before I check with our council planners.