Roof Window vs. Skylight: They're Not the Same Thing

People use these two words interchangeably and they aren't interchangeable. The difference is real, it's defined by how the unit is installed and whether you can reach it, and it determines what you can legally use the opening for.

Here's the distinction, and then the part we care about most as a metal shop: the flashing, which is where nearly every one of these leaks.

The Actual Difference

A roof window installs in the same plane as the roof deck, at a minimum roof pitch – typically around 15 degrees. It's positioned where you can reach it, it's operated manually by hand, and it opens wide. Some models open far enough to qualify as an egress exit, which matters for a finished attic or a converted room in a roof.

A skylight is the broader category and covers units mounted out of reach. It can be curb-mounted, which gives it far more installation flexibility, including on low-slope and flat roofs. A venting skylight opens only a few inches – enough for air, not enough to climb through – and out-of-reach units are operated by a pole, or electrically or solar-powered with a remote. Fixed skylights don't open at all.

Put simply: a roof window is a window you can reach and climb out of. A skylight is a light source overhead that you probably can't reach and definitely can't exit through.

Which One You Actually Want

Choose a roof window if: you're finishing an attic or a room in the roof, the opening is within reach of the floor, you want real ventilation, or you need the opening to satisfy an egress requirement for a bedroom.

Choose a skylight if: the ceiling is high and the unit will be out of reach, the roof is low-slope or flat, you mainly want daylight rather than air, or you want powered operation and automatic rain sensors.

For most DFW homes with standard ceiling heights, the answer is a skylight. Roof windows show up in the specific case of a converted attic space, which is less common here than in markets with older housing stock and steeper roofs.

Curb-Mounted vs. Deck-Mounted

This is the choice that actually affects whether the thing leaks.

Deck-mounted units sit low and integrate with the roofing plane. They look better – a much lower profile from inside and out – and they use a manufacturer's step-flashing kit that ties into the shingle courses.

Curb-mounted units sit on a built-up frame, the curb, which raises the unit above the roof plane. The curb is typically framed lumber, and the metal work wrapping it is what keeps water out. It's the only practical option on low-slope roofs, and it's how most replacement units go in over an existing opening.

The curb is where we get involved, because a curb is only as good as the metal wrapped around it.

Why Skylights Leak (It's Almost Never the Glass)

A skylight that leaks is almost always a flashing failure, not a glass or seal failure. The usual suspects, in the order we find them:

• Sealant used instead of flashing. Someone bedded the unit in caulk and called it done. Caulk is a five-year material on a Texas roof. It bakes, cracks, and fails, and then water goes straight into the opening.
• Head flashing missing or wrong. The uphill side of a skylight takes the entire water load coming down the roof. It needs a proper head flashing or a cricket, and on wider units it needs a cricket, full stop.
• Step flashing not woven into the shingle courses. Continuous flashing run down the side instead of properly stepped is a leak waiting for the first driving rain.
• A rotted curb. Water got in years ago, the framing softened, the unit settled, and now nothing seals because nothing is straight.
• Hail damage to the flashing. North Texas hail dents and splits thin aluminum flashing. The skylight looks fine and the flashing beside it is compromised.

The metal is the system. The glass unit is a component sitting inside it.

What We Do With Skylights

We're a metal fabrication shop, not a skylight distributor, so our role here is the part that fails: fabricating curb wraps, head flashing, crickets, and counterflashing in copper or stainless for skylight and roof window openings.

That matters in this market for the same reasons it matters on chimneys. Thin aluminum flashing dents in hail and corrodes where it contacts masonry. Copper and stainless don't. Our breakdown of copper flashing vs. aluminum and stainless covers the metal comparison in full, and everything in it applies to a skylight curb as directly as it does to a chimney.

If a skylight has been leaking long enough that the curb framing is soft, that gets rebuilt before any metal goes on. Wrapping good copper around rotten lumber solves nothing.

Comparison Table

FAQ

What is the difference between a roof window and a skylight?

A roof window installs in the roof plane within reach, opens manually and wide, and some models qualify as an egress exit. A skylight is typically out of reach, can be curb-mounted on low-slope roofs, and either doesn't open or opens only a few inches.

Can a skylight count as an egress window?

Generally no. Venting skylights open only a few inches. Some roof windows do qualify as egress, but that depends on the specific model meeting the opening dimensions your code requires, so confirm it against the model before you rely on it.

Why is my skylight leaking?

Almost always the flashing rather than the unit itself. The most common causes are caulk used in place of real flashing, a missing head flashing or cricket on the uphill side, and step flashing that wasn't woven into the shingle courses.

What is a skylight curb?

A raised frame the skylight sits on, lifting it above the roof plane. It's standard on low-slope roofs and on replacement installs. The metal wrapping the curb is what actually keeps water out.

Should skylight flashing be copper or aluminum?

Aluminum works on a straightforward roof and costs less. Copper or stainless is worth it where hail is a concern, where the flashing contacts masonry, or on a house you intend to keep, because it won't dent, corrode, or need replacing with the next roof.

Get a Free Quote from Autograph Construction

If a skylight is leaking, the flashing is the place to look first. We fabricate custom curb wraps, crickets, head flashing, and counterflashing in copper and stainless for homes across the Dallas–Fort Worth metro. Contact Autograph Construction and we'll come look at it and tell you what it actually needs.

Questions? Call (945) 231-3781