This depends on the space available and homeowner preference. Casement windows swing open on a hinge, which allows them to open all the way, creating a wider window opening. Sliding windows only open part of the width of the window. Sliding windows may have a slight edge in that they have fewer moving parts, which lowers overall maintenance costs. The average cost to install a sliding window is around $725, and the average cost to install a casement window is $855.