What length hinge is on the transom?
Isnt the transom the horizontal bar between upper and lower window
If so I don't understand the question
Pedant Transom is the bar, but the opening window/vent above is also known as a transom
Sorry I wasn't, I had to google transom.....and every pic I looked at said it was the middle bar.....
Was only joking
10" hinges are not manufactured in "restrictor" form. (See my amended post). As previously suggested, if access is via a flat roof, even a window on the "night latch" can be forced. If you want airflow you can fit a "tricklevent" into the head of the frame or opener but my advise would be to keep the window shut when property unoccupied.
I purposely avoided windows with, as you say, a 'tricklevent'. To me, what is the point of having a doubled glazed window when a slot has been cut through the frame and a flappy paddle installed, which you just open and close....hardly draft prove or adding to the double glazing point. My windows open about 1/2" then you can lock them in that position....the locking mechanism is all metal and I would like to think that even if you got a crow bar of them when in that position, you would just snap bit of plastic off without actually getting the window open. As I said in my OP, the 1/2" they open isn't enough for adequate ventilation, so a 'tricklevent' isn't going to cut it either....