just curious, for those whose sliding windows can be lifted open from corridor, is there an add on angle strip on the bottom rail? if not, then yes you can lift up the window easily. did it all the time for cleaning. the permanent angle strip prevent the sliding windows from coming off the rails. http://www.hdb.gov.sg/fi10/fi10297p.nsf/ImageView/NEW_SLIDING/$file/Window-08-Model.pdf