Stop Corrugated Metal Roof Leaking

I’ll tell you the most common mistake I see every month in Nassau County: a homeowner notices drips or rusty stains along their corrugated metal roof, buys a few tubes of silicone caulk, and smears it over every screw head, seam, and edge they can reach. Then after the next nor’easter, they call us because now they’re leaking in three different places instead of one. That approach doesn’t stop corrugated metal roof leaking-it traps water under the sealant skin, speeds up rust, and makes it harder to find the real problem later. Most corrugated roof leaks come from a handful of predictable detail failures-failed fasteners, wrong lap sequences, missing closure strips, and lazy flashing work-and if you understand those causes, you can fix the leak correctly the first time or at least know what questions to ask before hiring someone.

This article walks you through the real diagnostic steps, explains why corrugated roofs leak where they do, and gives you repair options that match the scale of your problem. We’ll also make it clear when you should tackle it yourself and when you need a professional crew-because a ten-foot-high carport roof in your backyard is a very different risk than a two-story garage or a metal roof over your living space.

Step 1: Locate the Real Source of the Leak

Water doesn’t always drip straight down. On corrugated roofs it loves to travel along ribs, run sideways on purlins, or track along the underside of panels before it finally shows up as a stain or puddle twenty feet from where it entered.

Start Inside, Then Work Outward

If you can safely access the underside of your roof-in an attic, garage loft, or under exposed beams-start there on a sunny day after a rain. Look for wet streaks, water trails, or damp insulation and mark those spots. Then go outside and inspect directly above those interior marks, plus upslope from them, because water can enter high and run down before it drips. Check in dry conditions with good light so you’re not just guessing at shiny wet spots.

Common Leak Locations on Corrugated Roofs

• Screw or nail lines where fasteners have backed out, gaskets are split or missing, or screws are driven in the wrong place (valleys instead of crests).
• Panel overlaps and side laps where the next sheet covers the last one; if the overlap runs the wrong direction or sealant is missing, wind-driven rain sneaks under.
• Transitions at walls, chimneys, and parapets where flat flashing meets the corrugated profile without proper closure strips or step details.
• Ridge caps, eave trim, and end laps at the top and bottom of the roof, especially where foam closures are skipped and birds or water get into the open ribs.
• Cut-in penetrations for vents, pipes, skylights, or service masts that interrupt the panel and weren’t detailed correctly.

Watch for Condensation Misdiagnosed as Leaks

In humid Nassau summers and sudden cold snaps, uninsulated corrugated metal can sweat on the underside and drip like a roof leak. If you see moisture forming broadly across the metal in cool, damp weather-not just after rain-you might be dealing with condensation, which requires different fixes like vapor barriers, ventilation improvements, or insulation upgrades rather than screw replacement and flashing work.

Step 2: Diagnose Why Your Corrugated Roof Is Leaking

Once you’ve narrowed down where water is entering, you need to understand why that spot is failing so you can fix the root cause instead of just covering symptoms.

Fastener Failures

Corrugated roofs use hundreds or thousands of exposed screws or nails, and over ten or fifteen years thermal expansion and wood movement cause them to back out slightly or shift. The rubber or neoprene washers under screw heads dry out, crack from UV exposure, or get crushed by over-tightening during the original install, creating tiny gaps where capillary action and wind pressure drive water in. On a carport in Freeport last fall we counted forty loose screws along just three rows of panels-every one had a rusty water stain running down from it. When you walk your roof and see rows of rusty or stained screw heads, that’s your smoking gun that fastener lines are leaking.

Panel Overlaps and Side Laps

Corrugated and ribbed panels rely on correct side-lap overlap-usually one full corrugation or rib-and the overlap must shed water downhill, not trap it. If screws are placed through both layers in the wrong spot, or if panels aren’t aligned so ribs nest properly, water can track along the underside or pool in the low ribs where laps meet. On low-slope roofs (anything under 3:12) or on long runs exposed to Nassau’s coastal winds, even a correctly overlapped seam can let water in unless you add butyl lap sealant or tape between the panels. I’ve seen dozens of garage roofs where the installer just overlapped the sheets dry, no sealant, and within two years wind-driven rain from nor’easters was pushing water up under those laps and dripping inside.

Flashing and Transition Problems

Where corrugated metal meets house walls, chimneys, parapets, or other roofs, the flashing details must follow the panel profile and send water over the top of ribs, not behind or under panels. Flat wall flashing laid over corrugations without foam or rubber closure strips leaves open channels where water runs in. Step flashing that doesn’t account for the rib height creates the same problem. On a workshop in Levittown we found a contractor had nailed flat aluminum against the wall, right over the corrugated ribs, with no closures and no counterflashing-water was pouring in every time it rained hard, tracking along the wall framing and rotting the rim board. These transition leaks are slow, hidden, and expensive if they’re ignored, because the damage spreads behind siding and into structure before you even notice wet drywall or stains inside.

Step 3: Safe, Effective Repair Options for Corrugated Metal Roofs

Now that you understand why corrugated roofs leak where they do, here are the main repair strategies that actually work-and the shortcuts that don’t.

Replace Failed Fasteners, Don’t Just Caulk Them

The durable fix for leaking screws is to remove the failed fasteners and install new ones-ideally one size larger in diameter, with fresh neoprene or EPDM washers rated for UV and coastal conditions-into solid purlins or substrate. Don’t just smear caulk around old screws and call it done; that traps moisture, looks terrible after a few months, and usually fails in the next heavy storm. On small, accessible roofs like sheds or one-story porches, experienced DIYers can handle rows of fastener replacement if they’re comfortable on ladders and follow safety precautions. For large, steep, or high roofs, hire a pro who can work safely and has the right tools to pull and reset fasteners without bending panels.

Re-Sealing Side Laps and End Joints

If side-lap leaks are the problem, you can sometimes correct them by gently lifting the overlapping panel edge, cleaning both surfaces, applying compatible butyl lap sealant or peel-and-stick lap tape, and re-fastening in the correct location-through the crest of the rib, into both panels, so the lap is mechanically locked and sealed. Don’t just run a bead of generic silicone along the outside of the seam; that can trap debris and water and make future repairs harder. Use products designed for metal-to-metal laps and follow the manufacturer’s instructions on temperature, overlap width, and cure time.

Correcting Flashings at Walls and Penetrations

Improper wall or chimney flashing on corrugated roofs often needs to be removed and rebuilt with step flashing, closure strips to fill the ribs at the wall line, and counterflashing that sends water over the top of the metal and down the corrugations, not behind them. This is precision work; mistakes here lead to hidden wall damage, mold, and rot that can cost thousands to fix later. We strongly recommend hiring a roofer for these transitions on occupied homes or commercial buildings, especially in Nassau where wind-driven rain will find every small gap. On a two-story garage in Garden City we had to strip back siding, replace rotted framing, and install proper stepped closure and counterflashing because the original crew had just laid flat L-flashing over the corrugations with no closures-classic lazy detail that leaked for three years before the owner called us.

Treating Minor Rust and Preventing Future Leaks

Once leaks are stopped, lightly rusted areas around screws, cut edges, and panel ends should be cleaned with a wire brush, treated with a rust converter or inhibitor, and recoated with compatible metal primer and topcoat to slow further corrosion. This step matters more in coastal Nassau where salt air accelerates rust around small coating failures and exposed fastener heads. If rust has eaten through the panel or created pinholes, those sections need to be cut out and replaced-coating over rust-through is cosmetic only and won’t stop leaks.

DIY vs Professional Repair on Corrugated Metal Roofs

Be realistic about what you can safely do alone. Corrugated metal is slippery, sharp-edged, and unforgiving.

When DIY Might Be Reasonable

Handy owners might tackle limited fastener replacement, small lap re-sealing, or rust treatment on a low, easily accessed section of roof-backyard sheds, single-story carports, porch overhangs-if they’re comfortable on ladders, have proper footwear with grip, and work only in dry conditions. Use fall protection where required by height and slope, and don’t rush. Corrugated metal is extremely slippery when wet or dewy, and one slip can mean serious injury or worse.

When to Call a Nassau County Metal Roofing Pro

Steep roofs, high roofs (anything over ten feet), large areas with multiple leak sources, leaks involving walls or chimneys or living/commercial spaces, and situations where you suspect structural issues or widespread rust should be handled by insured professionals with proper equipment and experience. Local pros understand Nassau’s wind exposure, salt air corrosion rates, and code requirements, and they can recommend the right fasteners (stainless or coated), sealants (butyl vs. polyurethane vs. silicone for metal), and flashing designs that will last ten or fifteen years, not just survive the next storm. If you’re not sure, get an inspection; most reputable roofers will give you a straight answer about whether you need full repairs, a few targeted fixes, or if the roof is at the end of its service life.

Common Mistakes That Don’t Actually Stop Corrugated Roof Leaks

Save yourself time, money, and frustration by avoiding these tempting shortcuts.

Smearing Caulk Over Everything

Coating every screw head, seam, and crack with generic caulk without removing failed hardware, cleaning rust, or fixing alignment issues creates a temporary skin that cracks, peels, and traps water within a season or two. Worse, it makes proper diagnosis nearly impossible later because you can’t see where fasteners are loose, where laps are misaligned, or where panels have pulled away from purlins. Sealants work best as part of a mechanical repair strategy-new fasteners, correct overlaps, proper flashing-not as the only tool in your repair kit.

Ignoring Slope and Drainage Problems

On very low-slope corrugated roofs (anything under 2:12, and especially under 1:12), water can linger in valleys and at panel ends, overwhelming laps and sealants no matter how well you repair fasteners and details. If your corrugated roof was installed on too shallow a slope for its profile-common on carports, lean-tos, and cheap additions-you may need larger design changes like adding slope, switching to a standing seam system, installing an underlayment membrane, or even re-framing the structure to get proper drainage. Repeated small fixes on a fundamentally under-sloped roof just buy you months, not years.

Local Considerations: Corrugated Roofs in Nassau County’s Weather

Nassau’s coastal climate and storm exposure create specific challenges for corrugated metal that inland or calmer regions don’t face.

Wind-Driven Rain and Nor’easters

Sideways, wind-driven rain during nor’easters and tropical remnants can push water up under panel laps, against eave trim, and into wall flashings, exposing weaknesses that don’t show in gentle, straight-down rain. I’ve seen roofs that were bone dry in summer showers leak like sieves during October and March coastal storms because the laps and fasteners weren’t detailed for horizontal water pressure. Repairs and new installs on corrugated roofs here should be designed with those worst-case wind events in mind-tighter laps, more sealant, better closure strips, and fasteners every twelve inches instead of every eighteen.

Salt Air and Fastener / Panel Life

Near bays and the Atlantic, untreated or low-grade galvanized screws and panels rust faster than they would twenty miles inland. Leaks often show up as gasket failure or pinholes around fasteners within five to eight years instead of fifteen. Coastal repairs should use stainless steel or heavily coated fasteners, compatible butyl or polyurethane sealants that stay flexible in salt air, and sometimes upgraded panels with better coatings (Galvalume, painted steel, or aluminum) to avoid re-leaking in just a few seasons. Skimping on fastener and material quality near the water is penny-wise and pound-foolish.

Frequently Asked Questions About Corrugated Metal Roof Leaks

Can a corrugated metal roof be repaired, or does it need to be replaced?
Many leaking corrugated roofs can be repaired successfully with fastener replacement, lap corrections, flashing rebuilds, and rust treatment, especially if the underlying panels and structure are still sound. Roofs with severe rust-through, major structural sagging, or very poor slope (under 1:12) may be better candidates for replacement or switching to a different roofing system. A thorough inspection can tell you which path makes sense for your situation and budget.

Will a roof coating alone stop my corrugated metal roof from leaking?
Coatings can help extend roof life and seal minor surface issues, but only if you prep the roof correctly and fix mechanical problems first. Putting coating over loose fasteners, bad laps, or failing flashings rarely stops leaks for more than a few months; water will still get in through the gaps, then sit trapped under the coating and accelerate rust. Fix the details, then coat if you want extra protection.

Why does my corrugated roof leak only in heavy wind and rain?
Wind-driven rain can push water up under laps, behind trim, and into gaps that don’t leak during gentle, straight-down showers. This indicates detail issues at seams, flashings, or fasteners, not that your metal is “worn out.” The fix is usually tighter overlaps, better sealant, proper closure strips, and sometimes additional fasteners to hold panels flat against wind uplift.

How long will repairs on a corrugated metal roof last?
Well-done repairs using quality stainless or coated fasteners, compatible sealants, and correct flashing details on otherwise sound panels should last ten to fifteen years or more. Heavily corroded roofs, roofs with design flaws (too low slope, inadequate fastener spacing), or roofs near the coast with cheap materials may only get shorter-term relief-three to five years-before more work is needed.

Do you repair corrugated metal roofs across Nassau County?
Yes. TWI Roofing inspects and repairs corrugated roofs on homes, garages, barns, carports, and light commercial buildings throughout Nassau County. We can schedule an on-site leak evaluation, identify every problem area, and give you a detailed estimate for permanent repairs or replacement if that makes more sense. Bring photos or notes on when and where leaks occur so we can get to the root cause quickly.

Stop Corrugated Metal Roof Leaks Before They Get Worse

Most corrugated metal roof leaks come from fixable details-fasteners that backed out, laps that weren’t sealed or were done in the wrong sequence, and flashing work that skipped the closure strips and proper step details-not from the entire roof being “shot.” The right repair approach combines correct mechanical fixes with targeted sealing and, especially in coastal Nassau, corrosion-resistant materials matched to your exposure level and roof height.

Use the diagnostic steps in this article to understand where your leak likely originates, then decide whether you can tackle a small, low section yourself or if you need a qualified local roofer for steep, high, or complex work tied into your home or commercial building. If you’re seeing drips, rust stains, or interior water damage on a corrugated metal roof anywhere in Nassau County, contact TWI Roofing to schedule an inspection. We’ll walk the roof, explain exactly what’s failing and why, and give you repair options that stop the corrugated roof leaking for the long term-not just until the next nor’easter rolls through.