Velux | Curb Mounted, No Leak Fixed Skylight The skylight is energy efficient with LowE3 coating. There isn't a designated top, bottom or sides so can be installed in any direction. Has a maintenance free frame. Inside curb dimensions are 22 1/2" x 22 1/2" and the outside curb dimensions are 25 1/2" x 25 1/2". FCM 2222