Before you take any measurements, you need to decide whether you want the roller shutter mounted on the wall or mounted inside the reveal/recess of the window. See pictures below for illustrations
MOUNTED ON WALL
This is one of the simplest ways to measure and fit DIY roller shutters. With this type of fixing the header box and guides are fixed directly onto the wall outside the window frame.
This is suitable for all window and door openings. However, your window/door frames or handles extend beyond the wall you will need to use packers when fixing your roller shutters.
MOUNTED IN THE WINDOW REVEAL/RECESS
With this mounting method the header box and guide rails are mounted inside the external window reveal/recess.
This method requires precise measurements as there is no room for error. To mount the roller shutter in the recess you will require a recess depth of at least 40mm.
If your windows open outwards such as casement, awning or hopper windows it is recommended that you choose the on wall mounting method as the guide rails mounted inside the window recess could interfere with the operation of the window.