Roofing component
What is a skylight?
A window in the roof — a hole in the most important weather barrier of the house, made safe by the right glass and the right flashing.
Updated September 12, 2026 · Every figure links to its source · Sources
DefinitionComponentAlso called: roof window, roof light, tubular daylighting device (TDD)
Skylight — a glazed unit set into a roof to admit daylight, either fixed or openable, mounted on a raised curb or directly on the roof deck and flashed into the surrounding covering; the 2021 IRC, Section R308.6 regulates skylights and sloped glazing, naming the glazing types allowed, and the NRCA glossary records the term.
What it is
A curb-mounted skylight sits on a wooden box, the curb, that rises several inches above the roof; the glazing unit caps the curb and the roof's flashing runs up the curb's sides. A deck-mounted skylight is a self-flashing unit fastened directly to the sheathing, with a manufacturer's flashing kit woven into the shingles. A tubular daylighting device is a small rooftop dome that feeds a reflective tube to a ceiling diffuser, for rooms without attic access to the roof above. Openable ("venting") skylights add a hinge and, often, a rain sensor.
The glass is regulated because it is overhead. The IRC, Section R308.6 permits laminated glass, fully tempered glass, heat-strengthened glass, wired glass and approved plastics, with rules on when a screen is needed beneath tempered glass and on the size and slope of plastic glazing. The joint with the roof is regulated as a roof opening under the IRC's flashing rule, Section R903.2.1.
Why it matters
Skylights leak — but mostly at the flashing, not through the unit. Water runs down the slope and meets the uphill side of the curb, where a saddle or cricket-shaped head flashing should turn it aside; step flashing runs down the sides and an apron finishes the bottom. A skylight installed with a bead of sealant instead of that sequence leaks in the first heavy rain from the uphill side; a good one lasts as long as the roof. The second source of "leaks" is condensation: a single-glazed or metal-framed unit in a cold climate drips in winter from the inside.
Skylights are also the roof's weak point in hail and in falling branches, and the unit's own life — seals, gaskets, the plastic of older bubble domes — is shorter than a roof's. A re-roof is the moment to replace them; roofing over an old skylight and flashing it again is a saving that comes back as a leak. The directory's guide to finding a roof leak treats skylights as a first suspect.
What it costs and who does it
Replacing a skylight in kind is priced per unit plus the flashing kit and the shingles disturbed around it, and is cheapest on a re-roof; adding a new skylight where none exists is a carpentry job as well — cutting and headering the rafters, building the light shaft through the attic, drywall and paint — priced as a small project. Roofing contractors do replacements and the roof side of new installations; a carpenter or remodeller does the shaft and finish. The directory's roof repair cost guide explains how a replacement is estimated.
Frequently asked questions
Short answers; the sections above carry the detail and the sources.
Do skylights always leak?
What is the difference between curb-mounted and deck-mounted skylights?
Should skylights be replaced when the roof is replaced?
Next step
Find a roofer who does this
Skylight work is flashing work, and it should be priced as a named line, not buried in "misc". The directory lists roofing contractors by state and city.
Sources
- 2021 International Residential Code, Chapter 3: Building Planning — International Code Council (ICC)
- Roofing glossary — National Roofing Contractors Association (NRCA)
- 2021 International Residential Code, Chapter 9: Roof Assemblies — International Code Council (ICC)