Skylight Flashing Kit: The Part That Keeps Your Roof Dry

Almost every leaking skylight is not a leaking skylight at all, it is a failed or missing flashing job around it. A proper skylight flashing kit is the layered metal system that channels water around the skylight and back onto the roof, and it is the single most important component for a watertight installation. Buying the correct skylight flashing kit means matching it to your exact skylight model, your roofing material, and your roof pitch. Get any of those wrong and water finds its way in. This guide explains the kit types, sizing, and how the flashing goes together.

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What a Skylight Flashing Kit Includes

A flashing kit is not one piece but a coordinated set of metal components designed to shingle water away from the curb of the skylight. A typical kit contains a sill (apron) flashing for the bottom, head flashing for the top, step or channel flashing for the two sides, and often self-adhesive underlayment strips.

The pieces work by overlap. Water running down the roof hits the head flashing at the top, is diverted around the sides by the step pieces, and sheds off the apron at the bottom onto the shingles below. Each piece tucks under the roofing above it and over the roofing below, so gravity keeps water on top of the metal at every seam. This layering, not caulk, is what makes a skylight watertight.

Deck-Mount Versus Curb-Mount Kits

Skylights come in two mounting styles, and the flashing kit must match:

• Deck-mount (deck-mounted): the skylight sits low, fastened directly to the roof deck with an integrated frame. Its flashing kit hugs the low profile and gives the sleek modern look. Velux and Fakro deck-mount kits are model-specific.
• Curb-mount: the skylight sits on a raised wooden curb, usually 2-by-4 or 2-by-6 lumber, built up off the roof deck. The flashing wraps that taller curb. Common in retrofits and flat-roof applications.

You cannot use a curb-mount kit on a deck-mount skylight or vice versa. Confirm which style you have before ordering, because the geometry and the way the metal folds are entirely different.

Sizing the Kit to Your Skylight

Flashing kits are sold by skylight size and model, not as a universal product. Manufacturers like Velux publish size codes, for example a C01, M04, or S06, that correspond to specific rough-opening dimensions, and the matching flashing kit carries the same code.

Order the kit by that exact code plus your roofing type. Buying a generic or wrong-size kit leaves gaps the water exploits. Also match the flashing to your shingle profile; standard kits suit asphalt shingles, while low-profile kits (often labeled EDL versus EDW) are made for thin coverings like slate or metal, and high-profile kits handle tile. Using an asphalt kit on a tile roof leaves voids that leak.

Matching Flashing to Your Roof Pitch

Roof slope affects how water behaves around the skylight. Most flashing kits are rated for a minimum pitch, commonly 15 degrees (about a 3:12 slope) up to steep pitches. On a low-slope roof, water moves slowly and pools, so the flashing must have a taller upstand and you may need an additional underlayment membrane.

Below the kit’s minimum pitch, a standard skylight and flashing will leak no matter how carefully you install them; those roofs need a curb-mounted unit raised well above the water plane, often 6 inches or more, plus a fully adhered membrane. Always confirm your roof pitch falls within the kit’s rated range before buying the skylight itself.

Step-by-Step Flashing Installation

Installing flashing follows a strict bottom-to-top order that mirrors how water flows. Rushing or reversing the sequence causes leaks:

1. Apply self-adhesive underlayment around the skylight curb or frame, lapping it onto the deck and up the sides, sealing the nail penetrations.
2. Install the sill (apron) flashing at the bottom first, over the shingles below the skylight so water sheds onto them.
3. Work up the sides with step or channel flashing, each piece overlapping the one below and tucked under the adjacent shingle course.
4. Set the head flashing at the top last, sliding it under the shingles above so upper roof water flows over it and around the skylight.
5. Cover the head flashing with the roofing above, never leaving its top edge exposed to run-off.
6. Avoid relying on sealant for the primary defense; use it only as a secondary seal at overlaps the manufacturer specifies.

The golden rule is upslope over downslope at every joint. If any piece of flashing sits under the piece below it, you have created a funnel straight into the house.

Common Leak Causes and Fixes

When a skylight leaks, the flashing is almost always the reason. The usual culprits are worn or missing flashing on an aging install, reversed overlaps done by an amateur, or someone who relied on a thick bead of caulk instead of proper metal layering. Caulk fails within a few years, and then the water pours in.

Other frequent issues include debris damming above the head flashing, which forces water sideways, and corroded old flashing that has rusted through. The correct fix is rarely more sealant, it is re-flashing with a proper kit. If your skylight is over ten years old and leaking, replacing the flashing, and often the skylight, with a matched kit is the durable answer.

When to DIY and When to Call a Pro

A confident DIYer with roofing experience can install a flashing kit, since the manufacturer’s instructions are precise and the kit is engineered to fit. Budget a full day, work only in dry weather, and never on a steep or slick roof without fall protection.

That said, roof work carries real risk, both of injury and of a leak that damages the ceiling below. If your roof is steep, your skylight is high off the ground, or you are unsure about weaving flashing into existing shingles, hire a roofer. A professional flashing install typically runs $300 to $800 in labor per skylight, cheap insurance against a leak that could cost thousands in drywall and framing repairs. Whichever route you take, the right skylight flashing kit, installed in the correct order, is what keeps your roof dry for decades.

Matching Flashing to Your Roofing Material

The kit must suit the roof covering it ties into, and manufacturers make distinct versions for each. An asphalt-shingle kit is designed to lap over and under the shingle courses, and it is the most common. For a low-profile covering like slate, cedar shakes, or standing-seam metal, a low-profile kit sits tighter to the deck so water does not sneak under the thinner material.

Tile roofs, whether clay or concrete, need a high-profile kit with a flexible lead or malleable aluminum apron that can be dressed down over the contour of each tile. Trying to force an asphalt kit onto a barrel-tile roof leaves gaps under every curve, and those gaps leak in the first hard rain. Metal roofs often pair the flashing with a butyl or foam closure strip to seal the ribs. Confirm the kit is rated for your specific roof material before ordering, since the wrong profile is the second most common cause of skylight leaks after reversed overlaps.

Maintenance to Keep the Flashing Watertight

Even a perfect flashing job needs occasional attention to stay leak-free. Twice a year, and after major storms, look at the skylight from the ground with binoculars or from a safe vantage point. Clear leaves, pine needles, and debris that dam up above the head flashing, because standing water forced sideways is a classic leak path even when the metal is sound.

Check that the sealant beads at the manufacturer-specified overlaps are intact, and touch them up with a compatible roofing sealant if they crack with age. Watch for lifted or missing shingles around the flashing after wind events, and have them re-secured promptly. Inside, scan the ceiling around the skylight shaft for the faint brown staining that signals an early leak; catching it there, when it is a small flashing touch-up, is far cheaper than waiting until the drywall is soaked. Kept clear and inspected, a quality skylight flashing kit will protect the opening for the full life of the roof.

Re-Flashing During a Roof Replacement

The single best time to install fresh flashing is when the roof itself is being replaced. Old flashing that was fine under the previous shingles is often bent, corroded, or sealed with brittle caulk, and reusing it under a new roof is false economy. Any roofer worth hiring will recommend a new flashing kit whenever the surrounding shingles come off, because the labor to weave it in is already built into the tear-off.

This is also the moment to evaluate the skylight itself. If the unit is more than fifteen to twenty years old, its seals may be failing and the glazing may be fogged, so pairing a new skylight with new flashing under a fresh roof gives you decades of trouble-free service. Coordinate the timing so the flashing goes in with the roofing rather than as a separate visit, and confirm the new kit matches both the skylight model and the new roofing material. Doing it together is cheaper, cleaner, and far more watertight than flashing a skylight in isolation later.