I have a stucco house with relatively large aluminum framed horizontal sliding windows (RO is 70w x 58h)I know how to install a retrofit window of the same style but aside from not seeing that size available, I would prefer to have two side-by-side single hung windows in the space to give this boring 1980 tract house some much needed characterI\'ve seen it done (I think it was Bob Vila) using a 4x4 to divide the space vertically creating two or more separate window frames but that was part of a larger restoration project and the existing frame was removed down to the woodExterior siding and such had been removed as well)I want to leave the existing aluminum frame primarily to avoid water infiltrationCould I use this method or some variation of it using retrofit windows to leave my aluminum frame in place? Inside, my window returns are drywall with aluminum sillOutside, the windows are flush to the stucco.Thanks for any helpYou could leave your old frame in situ and fix your new windows to it, but realistically it\'s going to look like a dogs dinnerYou\'d be much better fixing your new windows to the brick or house framewhichever suits your particular situation and storm proofing the window with the appropriate moulds, I\'m guessing with a house of 30 years there would be no guaranty that you\'re not actually get any infiltration anywayAddition: I want to leave the existing ALUMINIUM frame primarily to avoid water infiltration You\'d have far more chance of having problems down the track if you do what you WANT You have 2 carpenters telling you that you\'re better off ripping your old windows out and fixing the new ones to the opening, yet you seem to know better I\'m sorry dude but to many guy\'s here Yahoo QA only want the answers that suit their own agendaI\'m pretty sure neither my learnered friend or I are trying to steer you wrongI\'ll tell you why it\'s better to start with a raw opening, because you can make a frame to fit your opening, once you have this frame you can build the windows into it using whatever trim, moulds, transom, mullions or divider panels so as to make it look good, I doubt leaving the old frame in the opening will look anything but ordinary.Other related question