A counterframe for a slidable door or window comprises: - a box structure (2) shaped for receiving internally- said sliding door or window and suitable for being embedded in a housing zone of a wall (3), and - acoustic insulating means (23) to acoustically insulate said housing zone, said acoustic insulating means comprising a soundproofing paint (23) applied to said box structure (2). A crosspiece element for counterframe for a slidable door or window, suitable for supporting and slidably guiding said sliding door or window, is provided. The crosspiece element is provided with positioning indicating means (18) incorporated therein to indicate whether said crosspiece element (12) is in a horizontal position. The invention further relates to a spacer element for maintaining in a fixing position a counterframe (1) for a slidable door or window, the spacer element comprising warning means (24) to warn of an inaccessible zone near said spacer element (8).