Sizing a replacement DG unit/ identify the manufacturer??

[ABCwarrior]

Our downstairs bathroom window has failed and needs replaced. I've calculated the entire unit is 22mm thick and it seems as if it would be replaced from the outside as the internal moulding on the frame is just too fine to allow any prying.
The windows are timber, I have no idea what company makes them ( and the bathroom has no privacy glass, and all the house has despite being 12 years old windows with those stupid click latches that a one armed person would never be able to close!! DDA friendly my ar#e) but there is evidence on the vertical beads that fine nails/ pins have been inserted. I'm assuming that to remove the unit these sides are removed working from bottom to top, then the (plastic)sill then the top bead. But how do I accurately size the width and height to order a replacement? Any advice I don't want to remove any bits yet, could I assume anything say 5/6mm less than the hard frame size, obviously excluding any beads???
Only Google searches I've come up with are really simple uPVC changes done from the inside...bet these effing wooden beads will end up snapped lol, and the unit would fail 4 months after I finally got round to repainting them all...
TIA....

 

[ronniecabers]

Yep , thats beaded from the outside , to be honest for some reason most Wooden frames are. As you say measure from where the bead meets the actual frame ( basically as if the beads had been removed ) , this is what is known as ' Tight Size ' . My only concern is if the system is a ' dry glazed ' system ( no silicone filling the void in the rebate around the sealed unit ) . If it is then that bottom bead will have packers underneath it and the bottom of the rebate will be sloped slightly to allow water run off, if it is then you need to allow an extra 5mm approx on your height. You could just measure the actual visible glass size width and height ...more commonly known as ' Sight Line ' , a good sealed unit manufacturer should know how much extra to add on for the sealant/spacer bar ( usually between 20-24 mm , depending on sealed unit manufacturer specification)
22mm is an unusual size for DGU's , I suspect probably that it is a 20mm Unit , utilising a 12mm silver spacer bar, but I may well be wrong. If the original units are under 19 years old ( fitted after April 2002 ) then they are probably ' low 'e glass as well, as this was a requirement for ENGLISH building control...I note you are in Invernesshire , so may be different

 

[ABCwarrior]

I used my digital vernier calipers to take the thickness of the window which was 54.75mm...then used my sinking square to take depths from internal/external frame to the glass which was 16.75/16mm so the unit must be 22....The windows are now about 13 years old, nothing would surprise me if this was some random obscure width and size from all the other bodges and howling workmanship I've unearthed over the years ha ha.
I'd like to take the beads off and check all measurements tbh but this is not the time of year for this kind of experimentation lol, wait until the summer and have some ply sheets to hand in case it goes south.
It's annoying that I can't even find out what make they are so that avenue of contacting the manufacturer is not there. The "hardware" on the windows(hinges,pivots,handles, frame runners etc) is the same as the windows where I work, they may be the same make and I think the building is only a couple of years older will need to inspect them....