The YES Ultimate Vertical Sliding Sash window is our most authentic uPVC sash window. The Ultra-Slim 35mm midrail, seamless construction and true mechanical joints provide an unmistakably classic solid timber look and feel. This sash window was one of the very first uPVC sash windows to be cleared for use in conservation areas. You get all that careful craftsmanship, historic detailing, and vintage appeal with all-round exceptional performance of twenty-first century uPVC.