What is the standard skylight size?
Why sizes follow the framing
Rafters and trusses are usually spaced 16 or 24 inches on center. With framing about 1.5 inches thick, the clear space between members is about 14.5 inches at 16 inch spacing and 22.5 inches at 24 inch spacing. Skylight makers size units to drop into those openings without cutting framing, and wider units span two bays, giving clear widths around 30.5 or 46.5 inches.
Common sizes you will see
- Narrow: about 14.5 inches wide, fitting one bay at 16 inch spacing.
- Standard: about 22.5 inches wide, the most common, fitting one bay at 24 inch spacing.
- Wide: about 30.5 inches, which usually means cutting a rafter and adding headers.
- Extra wide: about 46.5 inches, a larger structural change.
- Lengths: commonly from about 22 to 46 inches, chosen for how much light you want and the size of the ceiling opening.
- Tubular: roughly 10, 14 and 21 to 22 inch diameters, fitting between framing without cutting.
Deck mount vs curb mount
Deck-mounted skylights are sized by the rough opening in the roof deck. Curb-mounted skylights sit on a raised wood box, and they are sized by the outside dimensions of that curb, so a replacement must match the existing curb or the curb must be rebuilt. Each manufacturer uses its own size codes, so compare actual rough opening or curb dimensions rather than nominal names.
Replacing an existing skylight
Measure the rough opening or the curb, not the glass. Matching the old opening avoids reframing and drywall work in the light shaft. See replacing skylights with a new roof and roof anatomy explained.