Inside curb dimensions = 22 1/2" x 22 1/2". Designed for curb mounted installations, the VCE electric venting skylight is the ideal daylighting solution for overhead applications. It brings in abundant natural light and with the touch of a button, opens to let in fresh air. And if you forget to close it, the VCE also closes automatically in case of rain. Site-built curb and flashing provided by others. A VELUX step flashing kit for site-built curbs on shingle roofs is available. This model was created by the Blue Marble Project and has been approved by VELUX.