PVCU windows and Grade II listed buildings have historically been strangers. For planners and conservation officers, these buildings (and all too often, conservation areas too) have meant one thing only when it comes to windows: timber. Yet, in many cases, a modern timber window is inferior to its PVCU counterpart in terms of durability and thermal efficiency, not to mention more expensive. We wanted to develop a product that would give homeowners in listed and period buildings a genuine choice when they upgraded their windows. After much development and design work, the Genesis vertical slider was born. The Genesis VS.