The job I'm currently working on required the removal of two ugly 1970's dormers and their replacement with two Fakro conservation rooflights (Listed building - the idea being to restore the roof line).
The requirement for fire escape regs is that the bottom of the window opening should be <1100 mm from the floor. Now, as the regs take account of the problems presented by older buildings, in that you are frequently faced with a far-from-ideal situation not of your making and impracticable to change, the rule is that whatever you put in must not make the original situation any worse.
The bottom of the window opening of the dormers was 1510 mm high. The bottom of the rooflights was 1530 mm, both well over the ideal 1100 mm.
(You'd also normally fit an escape window onto a roof, but that height meant that the handle - on the side - would have been a stretch for a normal height person just to reach, let alone open to its full extent, and impossible for a child to reach. Luckily, as these were the largest of the Fakro windows, the centre pivot gave an opening actually wider than the original dormers, so I was able to use the pivots with the handle on the bottom.)
So how to get the occupants up to that required <1100 mm?
There is a radiator immediately beneath the window. Add a radiator cover and make it something else?
It's of 18mm MDF, any pattern of radiator grille panel, and a top section on each step of 30mm meranti (less likely to distort from the heat of the radiator).
To be certain of the thinking, I called the BCO in to check and he thought it was an excellent idea. I gave him a copy of the drawing and asked him to endorse it with his comment and keep it on the file for future reference, any subsequent change in BCO wouldn't mean an argument if they took a different view! He noted that the height of the 'step' actually reduced that required height to less than a metre, so the situation was actually improved.
It has to be fitted in a semi-permanent way, structurally secure but capable of removal to allow maintenance.