I have 4 Hotels that are traditional buildings, not porpouse built hotels and they have Sash windows, i am about to go WFP but due to the condition and age of the Sash i am not intending on using the WFP on them as the frames are FILTHY, and i mean super FILTHY, paint is flaking off and some of the frames are rotting and not exactly water proof if i use the WFP as the water will penetrate due to the angle of the brush.
They are high buildings and the job is done on all 4 of them every 3 weeks and i just do all the insides every 3 weeks and the outsides on the upper floors every 6 or 9 weeks, the buildings are far too high to use ladders so i the paint seal that was built up over many years and used the sash function and cleaned the outsides from the inside....major pain in the ass.
I have other Sash jobs but they are not much hastle and they will be easily converted to WFP.
Dont know if any of this helps.