Natural Light: Skylight Flashing for Metal Roofing

Sunbeams spilling into your kitchen or landing on your favorite armchair-that’s what a skylight’s supposed to deliver, and on a metal roof it absolutely can, but the difference between cozy natural light and a slow, nasty ceiling stain comes down almost entirely to how the flashing around that glass is built. This guide’s going to walk you layer by layer through proper skylight flashing for metal roofing so you can tell a real solution apart from a quick caulk job before water finds its way into your drywall.

Why Skylights and Metal Roofs Can Be Tricky Partners-And How Water Plays the Game

Honestly, I love metal roofs. They’re fast, tough, and they shed water like a champ when everything’s installed right. But they’ve got zero forgiveness if you introduce a glass rectangle into the middle of all those sleek, overlapping panels. Metal wants to move as it heats and cools, and a skylight curb is basically a stationary island in the middle of that motion. Water sees that island and gets curious-it’ll test the uphill corner first, looking for any gap between the curb and the roof, and then it’ll sneak down the sides, trying every seam. If the flashing isn’t built to control where water goes, you’re stuck chasing leaks that only show up when the wind blows sideways or the snow’s melting hard.

On a typical Nassau County ranch with a simple gable roof, that skylight’s probably sitting right over the upstairs hallway or the master bath, places where nobody thinks to look up at the ceiling until the stain’s already spreading. What most folks don’t realize is that the best skylight flashing starts before any shiny metal pieces get slipped under panels-it’s all about the curb height, the framing around the roof opening, and how the underlayment wraps and tucks around that opening to create a bulletproof base. Metal roof panels can handle wind, ice, and salt air just fine, but a poorly wrapped skylight curb turns your roof into a second-rate umbrella.

Around here-Hicksville, Westbury, Rockville Centre, all over Nassau-I’ve seen older colonials with four or five skylights punched into relatively low-pitch roofs, probably because the attic was finished decades ago and somebody wanted more head room and light. Those lower pitches (say 4:12 or 5:12) mean water moves slower, which gives it extra time to find trouble. When you add metal panels on top of that kind of pitch and drop skylights in without proper crickets and step flashing, you’re basically inviting water to sit and think about where it wants to leak next. So yeah, metal and glass can absolutely coexist, but only if you treat the skylight and the roof as one integrated system instead of two separate projects that just happen to meet.

Getting the Curb Height and Opening Right from the Start

Here’s the thing: the skylight curb has to sit high enough above the finished metal plane that water can’t capillary up into the curb base, but not so high that the flashing becomes a weird little tower that catches wind and looks ridiculous. For standing-seam or corrugated metal roofs around Nassau County, I aim for the curb to stand at least four to six inches above the finished panel surface, accounting for the panel profile and any underlayment buildup. That keeps snow melt and windblown rain from sneaking between the bottom flashing and the curb, especially when ice dams try to form along the uphill side during a February freeze-thaw cycle. If your roof pitch is steeper-like 7:12 or better-you can sometimes get away with the lower end of that range, but on lower pitches or coastal areas where nor’easters push water uphill, err higher.

The curb itself needs solid framing-typically doubled 2×4 or 2×6 lumber screwed securely to the rafters or trusses, then sheathed with plywood or OSB so you’ve got something stable to nail or screw your flashings to later. I’ve repaired too many skylights where the original installer just cut a rough hole, stuck the skylight unit on top, and hoped the factory flashing would do all the work. Water wants a steady, uninterrupted path to the gutter, and a wobbly, under-built curb interrupts that path in all the wrong ways, creating pockets where moisture sits and slowly works under your metal.

Building and Wrapping the Skylight Curb the Right Way

Most leaks around skylights don’t start where you think they do. They begin way below the visible metal flashing, down at the underlayment layer where laps and folds either shed water correctly or funnel it straight into the roof deck. Before I touch metal, I wrap that skylight curb like I’m gift-wrapping a box-every seam, every corner, overlapping in the right sequence so water can’t sneak uphill into a lap. Synthetic underlayment’s my go-to here because it doesn’t tear as easily as felt, and Nassau County’s mix of snow, heavy rain, and wind means I want something that can handle getting soaked and then drying out without turning into mush.

If you stand in your attic on a rainy day and look up at the skylight frame, you should see the underlayment wrapping up and over the curb sides in one continuous piece, with the top and bottom laps shedding water like shingles do. I start by laying the underlayment on the lower side of the curb first, letting it run up the curb face about six inches, then I fold side pieces over that, and finally the top (uphill) piece laps over everything. Any spot where water could flow *under* a lap instead of *over* it becomes a leak path, so I’m constantly asking myself, “If I were a raindrop crawling up this curb in a forty-mile-an-hour wind, where would I try to get in?”

Around the edges of the curb where the underlayment meets the roof plane, I’ll often add a narrow strip of peel-and-stick membrane-especially on the uphill side-to lock down any potential wind-driven moisture. Some guys skip this, figuring the metal panels will keep everything dry, but I’ve been called back to too many jobs where a nasty storm peeled up a panel edge just enough for water to wick into the underlayment, and without that sticky insurance layer the whole curb can turn into a slow-drip sponge. It’s one extra ten-minute step that saves a callback six months later when the homeowner’s staring at a water ring on their ceiling and wondering why the brand-new metal roof is already failing.

One more thing on the curb itself before we get to the flashings: insulation and ventilation. Back in Syosset one freezing February, I was called to a house where condensation was dripping off the skylight like it was raining indoors. The glass wasn’t the problem-the flashing and insulation around the curb were creating a giant cold bridge, so warm attic air hit that cold metal and turned into water. I re-flashed the whole skylight, wrapped the curb in an insulated curb extension, and adjusted the underlayment laps to let trapped moisture vent instead of pooling. That job taught me that skylight flashing on metal isn’t just about keeping rain out; it’s about managing how your roof breathes during Nassau County winters when attics can swing from freezing to sixty degrees in a single sunny afternoon. If you don’t account for that temperature dance, you’ll end up chasing “leaks” that are actually just sweating metal.

Underlayment Lapping and Curb Wrapping-The Foundation That Nobody Sees

The exact lapping sequence I use is this: lower curb underlayment first (running from the roof deck up the curb face), then side pieces that overlap the lower piece and run up the sides, then the top (uphill) piece that overlaps the side pieces and extends well down the roof deck to catch any water coming from above. Every single lap sheds water downhill, meaning the upper piece is always on top of the lower piece when you look at it from water’s perspective. If you reverse even one of those laps-say you tuck the top piece *under* the side pieces instead of *over*-you’ve just created a funnel straight into your roof deck.

In coastal Nassau-Atlantic Beach, Long Beach, anywhere the salt spray hits-I’ll also seal those laps with a thin bead of roofing mastic or compatible sealant, because the wind here doesn’t just push rain, it pushes foam and spray that can creep horizontally into seams you’d never expect to leak. It’s not about waterproofing the underlayment, since good synthetic is already waterproof; it’s about stopping wind-driven moisture from wicking between layers and sitting there until it finds a nail hole or a seam in the sheathing below. Little details like that are the difference between a skylight that lasts thirty years and one that starts weeping after the first serious nor’easter.

How Does Water Really Move Around a Skylight in a Metal Roof?

Here’s the blunt truth about skylights in metal roofs: water doesn’t just roll straight down the panels and call it a day. It wants to test every corner, every overlap, every spot where the metal profile changes, and the skylight curb is basically a big speed bump right in the middle of its journey. If you don’t give water an easy, obvious path around and past that speed bump, it’ll pool up on the high side, sneak along the edges, and eventually find any tiny gap in your flashing system. That’s why proper skylight flashing for metal roofing is really about building a series of controlled channels-metal-to-metal overlaps, step flashings, and uphill crickets-that tell water exactly where to go so it never has to think for itself.

Back on that windy Garden City job I mentioned earlier, I got called in October to a four-year-old standing-seam roof with three skylights that only leaked in sideways rain. Turns out the original installer had run full-length panels tight against the skylight curb with no cricket on the uphill side, so every time heavy rain came with a northwest wind, water pooled behind the skylight, found the tiniest seam in the head flashing, and snuck under. I rebuilt the curb, welded a custom metal cricket to the uphill side to split the water flow around the skylight, and installed a proper step-and-head flashing kit rated for metal roofs-not the generic stamped-tin stuff you’d use on asphalt shingles. Once water had a clear path to follow, the leaks stopped, and the homeowner hasn’t called me since, even through two brutal winters.

That uphill cricket is maybe the most skipped detail I see when I’m fixing other people’s skylight mistakes. Water hates being slowed down, so we give it an easy path by creating a little wedge of metal or framing on the high side of the skylight that diverts flow left and right instead of letting it pile up. Think of it like the prow of a boat: when water hits that angled surface, it splits and goes around. On metal roofs, I’ll fabricate a simple saddle out of the same material as the roofing-standing seam, corrugated, whatever-and set it so the top edge is higher than the curb and the sides taper down to guide water along the curb edges where the step flashing will pick it up. Here’s how I explain it to homeowners:

Water: “I’m going to hit this skylight head-on and sit here until I find a crack.”
You: “Nope, I put a cricket there, so now you’re splitting left and right.”
Water: “Fine, I’ll try sneaking down the sides.”

And that’s exactly where step flashing comes in. Along each side of the skylight curb, I install individual pieces of metal flashing-each one shaped like an “L”-that overlap each other like shingles and weave under the metal roof panels. Every piece laps over the one below it, so water coming down the side of the curb can’t reverse direction and get back under. On a standing-seam roof, those step flashings have to be custom-notched or bent to accommodate the raised ribs, which is why I always tell people that “universal” skylight kits from the big-box store are basically useless if you’ve got anything other than a flat panel. Factory kits assume a uniform surface; real metal roofs have profiles, and if your flashing doesn’t match that profile, you’re just creating gaps.

On coastal roofs-from Atlantic Beach to Long Beach-that step flashing also has to deal with the sea breeze that drives rain and sand horizontally in the afternoon. I’ve seen plenty of skylights that don’t leak in a straight downpour but start dripping when the wind swings around and pushes moisture up under the panels. For those situations, I’ll sometimes add a narrow strip of butyl tape or compatible sealant along the top edge of each step flashing piece where it tucks under the panel, not to glue things together but to give wind-driven spray one more barrier to fight through. It’s a small insurance policy that makes a huge difference when you’re two blocks from the ocean and every storm has a horizontal component.

Tying Skylight Flashing into Metal Panels-Step by Step

Once you’ve controlled how water hits the uphill side and guided it down the edges with step flashings, the next thing it will try is sliding under the downhill edge of the skylight, so that’s where your apron or head flashing at the bottom of the curb comes in. This piece sits on top of the metal panels below the skylight and tucks up under the skylight curb, creating one continuous sheet that water can ride from the glass down to the main roof without ever touching the curb base. On a standing-seam roof, that means carefully notching the flashing to fit over the ribs, and on a corrugated roof it means pre-bending the flashing to match the wave pattern-tedious work, but it’s the only way to keep water from finding the low spots between ribs and sneaking back toward the curb.

During a bright June in Long Beach, I retrofitted low-profile skylights into an existing metal roof over a beach house, timing the cuts and flashing work around the afternoon sea breeze that tends to drive sand and salt under loose laps. I insisted on pre-bending custom saddle flashings in my shop before we even touched the roof, because I’d seen factory “universal” kits fail when the metal roof’s rib spacing didn’t line up perfectly with the skylight width. We cut the panels, notched them to wrap the curb, hemmed the cut edges to prevent sharp burrs, and then slipped each flashing piece under the uphill panel and over the downhill one in sequence, making sure every overlap pointed the right direction. The homeowner wanted to use some generic kit he’d found online, but I showed him photos of three other beach houses where those kits had leaked within a year, and he let me do it right. Two seasons later, zero leaks, even through a couple of nasty northeasters that soaked everything else on his block.

Around the perimeter of the skylight, the metal roof panels themselves need to be cut and finished properly-not just hacked with tin snips and left raw. I’ll use a nibbler or a careful shear cut to trim the panel, then fold or hem the cut edge so it can’t catch wind or slice someone’s hand during future maintenance. Those cut edges then get tucked under the skylight’s side and top flashings, creating a layered system where every piece sheds water onto the piece below it. On standing-seam roofs, the seams themselves have to be clipped or fastened in a way that doesn’t interfere with the skylight flashings, which sometimes means adding a short false seam or a custom clip bracket near the skylight corners. It’s fiddly, precise work, but it’s the only way to preserve the roof’s designed water flow while introducing a big interruption like a skylight.

Once the Curb Is Properly Built and Wrapped, Insulation and Venting Matter Too

Back to that Syosset job for a second: the lesson I took from that cold-bridge condensation disaster is that metal roofs and skylights both conduct temperature like crazy, and if you don’t manage the thermal boundary around the skylight curb, you’ll end up with water problems that have nothing to do with rain. I now make sure the curb is wrapped with a layer of rigid foam or spray foam on the interior side (in the attic), creating a thermal break so warm attic air can’t hit cold metal and turn into drips. Some skylight manufacturers sell insulated curb kits; if yours doesn’t, you can build your own with foil-faced polyiso board and matching tape. It’s not glamorous work, but it’s critical in Nassau County where winter attics can swing between freezing at night and fifty degrees during a sunny afternoon, and metal just amplifies those swings.

I also make sure there’s an air path around the skylight-either by keeping the insulation a little bit back from the curb sides or by installing small vent channels-so any moisture that does sneak into the assembly can dry out instead of pooling and rotting the framing. This is especially important if your skylight sits in a cathedral ceiling where there’s no real attic to vent; in those situations, the skylight curb becomes a little island in the insulated envelope, and if you seal it up too tight without venting, you’re asking for mold and rot even if the flashing is perfect.

Relying on caulk instead of proper flashing geometry always fails eventually.

I can’t count how many skylight “repairs” I’ve undone where somebody just smeared a tube of silicone around the curb edges and called it waterproof. Caulk is your last line of defense, not your first solution, and on a metal roof where everything expands and contracts with temperature, caulk cracks and peels within a year or two, leaving you right back where you started-or worse, because now you’ve got old, dried sealant blocking proper drainage paths.

Common Nassau County Skylight Flashing Mistakes to Avoid

Most leaks around skylights don’t start where you think they do-they start at one of three spots: the uphill corner where the curb meets the roof plane (no cricket or poorly lapped underlayment), the side edges where step flashings either don’t exist or aren’t notched to match the metal panel profile, or the downhill edge where the apron flashing is too short or not properly overlapped by the roof panels. If you’re buying a house with a metal roof and skylights, or if you’re having skylights added to your new metal roof, here’s what to check: stand in the attic on a rainy day and look for daylight or moisture at those three spots. If you can’t get into the attic, look for stains on the ceiling near the skylight frame-they’ll usually show up at one corner first, and that corner will tell you which flashing detail was skipped.

Around Nassau-Garden City, Syosset, Long Beach, wherever-we see a lot of older skylights that were originally installed on asphalt shingles and then “adapted” when the roof was re-done in metal. That’s almost always a recipe for trouble, because the curb height, flashing geometry, and underlayment wrapping that worked fine on shingles doesn’t translate to metal without a complete re-build. If a contractor tells you they can just “flash around” your existing skylight when they’re putting on a new metal roof, ask them to walk you through exactly how they’re handling the uphill cricket, the step flashings, and the thermal break-and if they don’t have good answers for all three, call someone else. At TWI Roofing, we’ve re-done enough bad skylight installs that we can spot the warning signs from the driveway: curbs sitting too low, metal panels running straight into the curb with no flashing visible, or worst of all, a thick bead of caulk trying to hold back an ocean of water. Those details matter more than the skylight brand or the metal gauge-good flashing can make a cheap skylight work for decades, and bad flashing will sink even the fanciest glass in a year.

Your Quick Attic Inspection Checklist Before and After Skylight Flashing Work

If you’re having skylight work done or you’re troubleshooting an existing leak, grab a flashlight and head into the attic during or right after a good rain. Look at the skylight curb from below-you should see no daylight peeking through, no wet spots on the framing, and no water trails running down the curb sides or the rafters nearby. Check the underlayment laps: the top piece should be visibly on top of the side pieces, and the side pieces should be on top of the bottom piece, like overlapping shingles. If you see laps running the wrong way, you’ve found your leak source. Also feel around the curb for cold spots in winter or damp insulation-those are signs of a thermal bridge or missing vapor management. Honestly, most homeowners won’t catch every detail, but you’ll know if something’s seriously wrong, and that’s enough to have a real conversation with your contractor instead of just trusting that everything’s fine because the roof looks nice from the street.

On a typical Nassau County ranch with a simple gable roof, fixing a skylight flashing mistake usually means pulling a few metal panels, re-wrapping the curb with proper underlayment, fabricating or adding the missing cricket, installing real step flashings that match the panel profile, and then re-installing the panels with clean, hemmed edges. It’s a day or two of work for a crew that knows what they’re doing, and it’s way cheaper than letting a slow leak rot out your rafters and drywall over five years. If a contractor tries to sell you on “just sealing it up” without removing panels and inspecting the underlayment, you’re not getting a repair-you’re getting a temporary patch that’ll fail the next time we get a sideways nor’easter with forty-mile-per-hour gusts. Water’s patient, and it’ll wait for the next storm to prove my point, so do it right the first time and you’ll actually get to enjoy those sunbeams instead of mopping up puddles.

Bottom line: skylights and metal roofs can absolutely work together in Nassau County’s weather-salt spray, snow, wind, and all-but only if you treat the flashing as a carefully designed water-management system instead of a cosmetic trim detail. Every cricket, every step flashing, every underlayment lap, and every thermal break plays a role in keeping natural light where you want it and water where it belongs. When you’re vetting a contractor or planning your roof project, make sure skylight flashing for metal roofing is discussed in detail, not just tacked on as an afterthought. At TWI Roofing, we’ve fixed enough skylight disasters that we can promise you this: spending an extra afternoon getting the flashing right will save you years of headaches and a ceiling that actually stays dry. Water wants to test every seam, every corner, and every overlap-our job is to make sure it loses that game every single time.