Skylight Replacement: Velux vs Custom Curb-Mount

Skylights bring natural light into rooms that would otherwise feel like caves — top-floor brownstone bedrooms, rear additions, stairwells, and converted attics all benefit enormously. They also leak more often than any other roof penetration except chimneys. When it's time to replace one, the choice between a manufactured deck-mount unit (like Velux) and a custom curb-mount built on site has long-term consequences for maintenance, energy efficiency, and resale value.

This guide walks through what each option actually is, when to choose which, and what proper installation looks like.

Why skylights leak

Most skylight leaks aren't actually the skylight itself — they're the flashing where the skylight meets the roof. A skylight is essentially a hole in the roof with a window installed in it. The window itself is well-sealed at the factory. The flashing — the sequence of metal pieces that integrate with the surrounding shingles or membrane — is built on site and is only as good as the installer.

When a skylight starts leaking after 10 or 15 years, the cause is almost always failed flashing rather than failed glass. Replacing only the unit without replacing the flashing is a guaranteed callback. The image below shows a fresh skylight install with the integrated flashing kit being seated into the surrounding shingles — done right, this assembly stays watertight for 20+ years.

What Velux (and similar manufactured units) actually are

Velux is the dominant brand of pre-engineered residential skylights, but the category includes Fakro, VKR, and others. These are factory-built deck-mount units that come in standard sizes with matched flashing kits engineered specifically for that exact unit and that exact roof type.

The advantages are significant. Installation is faster because the flashing is pre-cut and indexed. Quality is more consistent because there's less site fabrication. Warranties are stronger — Velux backs the glass for 20 years and the flashing for 10. And replacement parts are available for decades, which matters more than people realize.

What custom curb-mount means

A curb-mount skylight sits on top of a wood or metal curb that's framed up several inches above the roof deck. The skylight is then mounted to the top of the curb, with site-built flashing wrapping around the curb and integrated into the surrounding roof.

Curb-mount makes sense in several specific situations: when the rough opening is non-standard (common in older NYC buildings), when the roof pitch is unusual, when the building has architectural constraints that prevent a standard deck-mount installation, or when a much larger skylight is desired than what's available off the shelf.

When Velux is the better choice

For most NYC residential skylight replacements — especially on standard asphalt-shingle roofs in single-family homes and small multi-family buildings — Velux or similar deck-mount units are the safer choice. The factory flashing kit eliminates the most common source of installation error. The standardization makes future repairs easier. And the warranty is meaningful.

If your existing skylight is already a Velux and the rough opening is intact, replacing it with another Velux is straightforward and quick.

When custom curb-mount is the better choice

Curb-mount is the right choice for non-standard openings, specialty glass (insulated low-E in oversized panels, for example), high-end architectural projects, and flat or low-slope roofs where deck-mount geometry doesn't work well. It's also the right choice when working with experienced sheet-metal craftsmen whose flashing work is genuinely better than what comes in the factory kit.

The catch is that curb-mount installation quality is enormously variable. A great installer will produce a curb-mount that lasts 30 years; an average installer will produce one that leaks in five.

Energy performance

Modern skylights have come a long way. Look for units with insulated glass, low-E coatings, argon fill, and a thermally broken frame. The Energy Star rating matters — a poorly performing skylight will radiate heat in the summer and condense moisture in the winter, both of which cause comfort and durability problems.

What proper installation includes

Whichever path you choose, proper installation always involves: removal of the existing unit and all surrounding flashing down to the deck, inspection and repair of any rotted decking or framing, installation of ice and water shield around the entire opening, the new unit (or curb), the manufacturer-specified or site-built flashing, and reintegration with the surrounding roof material.

The shingles or membrane above the skylight are always replaced, not just lifted and re-laid. Anything less is a shortcut that will leak.

What it costs

A standard Velux replacement on an existing opening runs $1,500-$3,500 installed, depending on size and roof complexity. Custom curb-mount installations start around $4,000 and can run well into five figures for large or architectural units. Both should include the matching flashing system and roof reintegration.

If your skylight has been leaking, do not just caulk it and hope. By the time water is visible inside, decking is already wet and probably rotted. Get it replaced properly the first time.