What is the average size of a skylight?
Why sizes cluster around framing
Most roofs are framed with rafters or trusses 16 or 24 inches apart. Skylight widths are designed to drop between them without cutting framing, so units fitting 24-inch spacing are typically a bit under 2 feet wide, and narrower units fit 16-inch spacing. Wider skylights require cutting a rafter and adding headers, which is a structural change that may need a permit and, with trusses, an engineer's input.
Common sizes
- About 2 by 2 feet. Small baths, closets and hallways.
- About 2 by 4 feet. The most common size for kitchens, family rooms and bedrooms.
- About 4 by 4 feet and larger. Great rooms and vaulted spaces, often requiring framing changes.
- Tubular skylights, 10 and 14 inch. Small spaces where a full skylight will not fit, routed through the attic.
Choosing the right size
A Department of Energy rule of thumb is to keep skylight area to about 5 percent of the room's floor area when the room has many windows and up to 15 percent when it has few. In Georgia, erring smaller limits summer heat gain. Two smaller skylights often light a room more evenly than one large unit.
Replacing an existing skylight
Measure the rough opening or the curb, not the glass. Replacement units are matched to the existing framed opening, and older curb-mounted units may be replaced with new curb-mounted models or reframed for a deck-mounted unit with a modern flashing kit.
See replacing skylights with a new roof and roof flashing explained.