Skylight Installation: Corrugated Metal Roof Integration

Yes, You Can Add a Skylight Without Turning Your Roof Into a Colander

Skylights on corrugated metal roofs don’t have to leak. I’ve been cutting openings in Brooklyn metal roofs for nearly two decades, and when you respect the panel shape, build a proper curb, and follow the right flashing sequence, your new skylight can outlast the rest of the roof without dripping a drop. This article is a leak-avoidance roadmap: I’ll walk you through every step, from choosing the right spot on your corrugated deck to sealing the last piece of trim, so you don’t end up chasing drips through three ceilings every time it rains.

The tricky part with corrugated metal isn’t the cutting-it’s making sure water doesn’t sneak under, around, or through the waves in the panels. Water loves corrugations. It’ll ride the valleys, pool behind fasteners, and creep sideways under trim if you don’t block every path. I think about it like a video game: every raindrop is trying to find the boss-level entrance to your living room, and your job is to build a gauntlet of flashing, sealant, and closure strips that stops it cold.

In Brooklyn’s climate, where we cycle between summer downpours and winter freeze-thaw, a sloppy skylight install shows itself fast. I’ve seen stains on ceilings two weeks after a bad curb job, and ice dams that turn a single mistake into a season-long nightmare. But when it’s done right-curb tall enough, flashing layered correctly, fasteners sealed tight-you forget the skylight’s even up there, except for the sunlight.

What Kind of Corrugated Metal Roof Are You Actually Working With?

Before you even touch a saw, walk your roof and figure out what you’ve got. Corrugated metal comes in different profiles-classic round waves, trapezoidal ribs, shallow box shapes-and each one behaves differently when you try to flash around it. Panel gauge matters too: thinner metal flexes more and requires tighter fastener spacing, while heavier-gauge steel stays put but needs bigger drill bits. If you’re on an old row house in Carroll Gardens or Cobble Hill, there’s a decent chance the corrugated metal was retrofitted over an earlier tar-and-gravel roof, which means you’re dealing with multiple layers, each with its own quirks.

Slope is critical. Corrugated metal roofs in Brooklyn range from nearly flat warehouse decks to steep-pitched retrofits over old timber framing. Anything under a 3:12 pitch needs extra attention to water pooling, and anything over 7:12 makes it harder to stand steady while you cut and flash. Measure your slope with a level and a tape, and plan your skylight location based on where gravity is already pushing water downhill-never in a valley where snow likes to drift or where two roof planes meet.

One January in Carroll Gardens, I installed a long, narrow skylight over a top-floor kitchen in a row house where the corrugated metal had been retrofitted over an old tar roof; the challenge was marrying the new curb to three different roof heights without creating an ice dam where the snow liked to drift. That job taught me to treat every corrugated roof as a custom puzzle: you’re not just cutting a hole, you’re integrating a new feature into an existing drainage pattern that was probably never meant to include a skylight in the first place. Look for existing fastener lines, rafters below, and any signs of rust or previous patches-those tell you where the weak spots are and where you need to beef up your framing.

Choosing the Right Skylight for Brooklyn Weather and Your Building Type

Match your skylight style to your roof and climate. Fixed skylights are simpler and cheaper, with no moving parts to leak or jam; they’re perfect for bringing light into an attic studio or hallway. Vented skylights add airflow but require curbs tall enough to keep rain out even when they’re open-plan on at least six inches of curb height, more if your roof is low-slope. For corrugated metal, I almost always recommend curb-mounted skylights over deck-mounted models, because the curb gives you a solid, square platform to flash against instead of trying to seal directly to the wavy panels. You want a skylight with aluminum or steel flashing kits designed for metal roofs, not the asphalt-shingle kits that come standard; the metal-to-metal interface seals better and won’t corrode in coastal salt air.

Building the Curb and Flashing It Like Brooklyn Weather Is Out to Get You

Your curb is the frame that raises the skylight above the roof plane and gives you a clean, vertical surface to flash. Build it from pressure-treated or cedar 2x lumber, sized to fit the rough opening your skylight manufacturer specifies-usually two inches larger than the glass in each direction. The curb needs to sit at least four inches tall on a steep roof, six inches on anything under 4:12, and taller if you’re venting or if snow drifts are common. Fasten the curb to the roof framing below, not just to the metal panels; I run screws through the curb, through the metal, and into solid rafters or blocking, using washers and neoprene seals on every fastener that penetrates the deck.

Here’s the part most people skip: closure strips and panel-profile matching. Corrugated metal has gaps under every rib where it sits on the curb. If you don’t fill those gaps, wind-driven rain will blow straight through. I use foam closure strips designed for the exact profile of the panels I’m working with-round, trapezoidal, or box-rib. Cut the strips to length, peel the backing, and press them down along the curb where the metal will land, then bed the metal edge into a thick bead of roofing sealant (butyl or polyurethane, never silicone-it doesn’t stick to metal long-term). On a Bushwick warehouse job last summer, I watched another crew skip this step entirely; by the first thunderstorm, they had water running down the inside of the curb like a little waterfall.

Flashing sequence is everything. Start at the low (downslope) side of the curb with your apron flashing, which tucks under the skylight and laps over the metal panels below. This piece sheds water away from the curb, so it needs to extend at least six inches down the slope and run up behind the curb at least two inches. Next, install your side flashings, each one lapping over the apron at the bottom and extending far enough upslope to tuck under the headlashing. Think of it as shingles made of metal: every piece overlaps the one below it so water can’t reverse direction. Leak Path Checklist: 1) Rain hits the skylight glass, runs down to the curb-apron flashing catches it and sends it over the panel ribs. 2) Wind blows water sideways under a panel edge-closure strips and sealant block the gap. 3) Melting snow tries to seep upslope under the headlashing-tall curb and proper overlap keep it outside the envelope. Finally, install your headlashing at the top, lapping over the side pieces and tucking under the skylight’s mounting flange. Every seam gets sealant, every fastener gets a neoprene washer, and every piece of flashing sits proud of the corrugations so water can’t pool behind it.

From a roofer’s point of view, fasteners are leak points waiting to happen unless you treat them like tiny roofs. Use metal roofing screws with bonded EPDM washers-these compress as you tighten them, creating a gasket around the screw shaft. Don’t overtighten; you want the washer snug, not squashed flat. Space fasteners about twelve inches apart along the curb and flashing edges, always landing in the high points (crowns) of the corrugations, never in the valleys where water runs. On steep roofs or in high-wind zones near the waterfront in Red Hook or Greenpoint, I double up fasteners at the corners and add an extra line mid-span to keep the flashing from lifting in a storm.

In Brooklyn’s climate, your flashing will face freeze-thaw cycles all winter and bake in summer heat that can soften sealant. I use high-temp butyl tape under all my flashing laps-it stays sticky in January and doesn’t melt off in July. For the final skylight-to-curb seal, the skylight itself usually comes with a foam gasket or requires you to run a bead of sealant around the curb top before you set the unit. Follow the manufacturer’s instructions exactly here, because that seal is your last line of defense. Once the skylight is fastened down, I go around the perimeter one more time with a thin bead of sealant, tooling it smooth so it doesn’t trap water but fills any micro-gaps.

Cutting the Opening Without Wrecking Your Panels

Measure twice, snap a chalk line, and cut once. Mark your rough opening on the metal from below if you can see the rafters, or from above using measurements from a reference point like a gable edge or chimney. A four-and-a-half-inch angle grinder with a metal cut-off wheel is my go-to tool for corrugated steel-it’s fast, reasonably clean, and doesn’t send sparks into your attic if you work carefully. Wear a full face shield and leather gloves; cut edges are razor-sharp and the panels vibrate like crazy. Start your cuts at a panel crown, not a valley, so you have a flat spot to hold the grinder steady. Work slowly through each corrugation, letting the tool do the cutting without forcing it, and have someone below catching scraps so they don’t slide down into gutters or onto your neighbor’s yard.

Dealing With Roof Layers and Vapor Barriers

If your roof looks anything like the older buildings in Park Slope or Fort Greene, you might find a layer of plywood, tar paper, or even old roll roofing under the corrugated metal. Cut through each layer carefully, and don’t assume the corrugated panels are doing all the waterproofing-sometimes they’re just cosmetic over a functional membrane below. When you frame your curb, make sure it ties into both the metal and the substrate so you’re not creating a gap where condensation or windblown moisture can sit. If there’s a vapor barrier or rigid foam insulation in the roof assembly, wrap the curb through it with peel-and-stick membrane or metal flashing to keep the thermal envelope continuous; a cold gap around your skylight curb will condensate all winter and rot the framing from the inside.

Mistakes That Turn Your New Skylight Into a Brooklyn Rain Feature

In Bushwick, I replaced a DIY skylight cut into a corrugated metal deck over a music studio-the owner had used wood screws meant for drywall and skipped the closure strips, so every nor’easter turned into an indoor rain show right over his mixing board. That’s the kind of mistake that costs you ten times the repair bill in damaged gear and lost work time. The biggest errors I see are undersized curbs that sit too low to shed water, missing or wrong-profile closure strips, and flashing installed upside-down so it channels water inward instead of outward. Each one creates a leak path that announces itself loudly the first time it rains hard.

Sealant abuse is another classic problem. Some folks think more is better, so they cake on thick beads that trap water instead of shedding it, or they use the wrong chemistry-silicone on painted metal, latex on raw steel-and it peels off in sheets after one winter. Others skimp and leave gaps, or they forget to seal fasteners entirely, turning every screw hole into a drip point. The right approach is thin, continuous beads in the right spots: under laps, around fasteners, and along panel edges where they meet the curb, with the bead shaped so water runs off, not into a little sealant bathtub.

Cheap or mismatched flashing is a nightmare waiting to happen. If you pair aluminum flashing with steel panels and steel fasteners, you’ve just built a battery: galvanic corrosion will eat through the aluminum in a couple of seasons, especially in Brooklyn’s salty coastal air. Stick with one metal family-all steel or all aluminum-and use compatible fasteners. Thin, painted trim-coil flashing might look fine at install, but it dents easily, holds water in the dents, and rusts through faster than you’d think. Invest in heavier-gauge, kynar-coated or stainless steel flashing for anything you expect to last more than five years.

Brooklyn-Specific Planning: Permits, Weather Windows, and When to Call the Metal Guy

On a cold Brooklyn morning in February, trying to install a skylight is a recipe for frozen sealant, slippery metal, and fingers that won’t work the drill trigger. Plan your install for late spring through early fall, when temperatures stay above fifty degrees and afternoon thunderstorms give you a clear morning work window. Check the three-day forecast and pick a stretch with no rain predicted; even if you tarp the opening overnight, wind can whip tarps loose and drench your interior. In the city, you also need to think about neighbors, noise ordinances, and where you’re going to stage ladders and materials on a narrow brownstone block with alternate-side parking and zero yard space.

Permits depend on the size and scope of your project, but in New York City, cutting a new opening in a roof generally requires a building permit, especially if you’re altering the structure or doing work on a building with more than three units. Call the Department of Buildings or check their website before you start, and if your building is in a historic district-common in Brooklyn Heights, Clinton Hill, or Prospect Heights-expect an extra layer of review from the Landmarks Preservation Commission. A small owner-occupied row house skylight might slide under the radar, but a larger project or anything on a rental property will need paperwork, inspections, and a licensed contractor’s signature. Metal Roof Masters can handle the permit process and the install, which is usually faster and less stressful than trying to DIY the bureaucracy.

One July, on a small warehouse near the Gowanus, we added a series of fixed skylights into a low-slope corrugated metal roof; I had to stage the work so the warehouse could stay open, cutting and waterproofing one opening at a time while forklifts buzzed around inside and humidity tried its best to warp every piece of flashing. That job reminded me that timing, staging, and having the right crew matters as much as technique. If you’re tackling this yourself, be honest about your skills: cutting and flashing corrugated metal isn’t rocket science, but it’s not forgiving either. One mistake with a grinder or a backward piece of flashing, and you’re looking at a leak that’s hard to trace and harder to fix. If you’ve never worked on a metal roof, consider hiring someone who’s done a hundred of them and knows how to think like water-it’ll save you grief and probably money in the long run.

Maintenance and Long-Term Thinking

Once your skylight is in, check it twice a year-spring and fall-by walking the roof and looking for lifted flashing, popped fasteners, or sealant that’s cracked or pulling away. Corrugated metal expands and contracts with temperature swings, so fasteners can work loose over time, especially the ones at panel edges near the curb. Tighten any that are backing out, add a fresh dab of sealant over the washer, and keep an eye on the closure strips; if one’s compressed or torn, replace it before the next storm season. Inside, watch the ceiling around the skylight for stains, soft spots, or peeling paint-those are early warnings that something’s leaking or condensing, and catching it early saves you from rotted framing or mold.

Let’s be specific about the metal: if your corrugated roof is painted or coated, touch up any scratches or cut edges where you exposed bare steel. Raw metal rusts fast in Brooklyn’s humidity and salt spray, and rust stains everything below it. A little spray paint or brush-on roof coating takes five minutes and adds years to your panels. If your skylight has an operable vent, keep the hinge mechanism clean and lubricated, and check the gasket around the vent flap; a torn gasket is an open door for rain, even when the skylight’s closed.

From a roofer’s point of view, a well-installed skylight on a corrugated metal roof should be virtually maintenance-free for the first decade, aside from those twice-yearly walkarounds and maybe a fresh bead of sealant here and there. If you’re chasing leaks every year, something was wrong at install-undersized curb, missed closure strip, incompatible metals, or flashing installed out of sequence. Don’t just keep patching; pull the skylight, inspect the curb and flashing, and fix the root cause. It’s less work than you think, and way cheaper than replacing water-damaged ceilings and insulation every few seasons. When you think like water-imagining every path a raindrop might take and blocking it with the right detail in the right order-you build a skylight install that outlasts the roof itself.