Consisting of two panels (leading and bottom) that slide up and down, our sash windows are counterbalance with pre-tensioned springs to hold the weight from the panels. This enables the window to be opened to any posture, also letting for the panels being operated with minimum effort. ordered secondary glazing https://chanceeoyhr.p2blogs.com/26003657/the-retrofit-double-glazing-in-london-w11-diaries