Skylight glossary

Curb — a raised wooden frame built on the roof that a curb-mounted skylight sits on. Deck-mounted — a unit fixed closer to the roof deck for a lower profile. Flashing kit — the manufacturer's set of metal parts designed for a specific unit and roof covering. Step flashing — individual pieces of metal woven in with each course of shingles along the sides of the unit.

Light shaft — the finished tunnel between the roof opening and a flat ceiling below. Splayed shaft — a shaft that widens toward the room, spreading light more broadly. Header — the framing member installed across a cut rafter to carry the load around the opening.

U-factor — how much heat the assembly loses; lower is better. SHGC (solar heat gain coefficient) — how much solar heat gets through; lower means less summer heat. NFRC — the National Fenestration Rating Council, whose certified ratings are the basis of ENERGY STAR skylight criteria, which vary by climate zone.

Tubular skylight / sun tunnel — a reflective tube that carries daylight from a small roof dome into a room below. Venting or operable skylight — one that opens, manually or by motor. Fixed skylight — one that does not open.

How to choose

Learn three terms before you meet a salesperson

Flashing kit, light shaft, and SHGC. Those three cover leaks, hidden cost and summer comfort.

Ask for the NFRC label numbers

U-factor and SHGC in writing on the quote makes two bids genuinely comparable.

Clarify mounting type early

Curb-mounted and deck-mounted need different flashing kits. Mixing them causes leaks.