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UNIT 5: LETTING THE LIGHT IN (WINDOWS & doors) INTRODUCTION Walls make a building strong, but they also make it dark. We need windows for light and fresh air. We need doors to go in and out. Parts of a Window A window has several parts. The frame is the outside part. It is fixed to the wall. The frame can be made of wood, plastic (uPVC), or metal (aluminum). Inside the frame is the sash. The sash holds the glass. Some windows open, and some do not. The glass is called the glazing. Modern windows