a window assembly of the type having at least one sash which is slidably mounted between a pair of jambs defining a window case , wherein the sash includes jamb - engaging side members which have generally flat edges . the flat or flush sides of the sash stiles allow the sash to be easily pivoted away from the plane of the window case , without pushing on , or deforming , the jamb liners , thus overcoming problems generally associated with conventional sash having recess or plows configured to be interfitted with protruding ridge - like channels projecting outwardly from the jambs , as is typically the case with wood - frame windows . in accordance with another aspect of the invention , weatherstrips are mounted to each of the jamb liners to provide weathersealing engagement between the jamb liners and the sash stiles at the sides of the windows . the weatherstrips provide an improved weatherseal as compared with known windows wherein weatherstripping is not provided between the window sash and jamb liner , including windows of the type having stile plows and interfitting jamb ridges . also , by attaching the weatherstripping to the jambs , as opposed to the sash , the extreme difficulty associated with reliably and cost - effectively anchoring a weatherstrip onto the stiles of a wood - type sash is avoided . another aspect of the invention provides a spring cover for completely concealing a tension spring used to balance the weight of a vertically movable sash .