I have a few custys that live in 3 storey town houses, that have sash windows, and often leave the lower sash open, so i txt the night before asking to ensure all windiws are closedi have washed a sash window before while the bottom was open i wont do that again i hope lol i couldnt see from the ground , i put the brush where i thought the glass was and realised it was open must of got it pretty wet inside no complaints luckily . at the time i thought theres bound to be a laptop / tv or something that could do without water on it