Dimensional Profile: Metal Shingle Roof Installation Guide

Blueprints sound fancy, but honestly all I want to give you here is a simple mental picture of how a metal shingle roof actually goes on-step by step, no jargon, and nothing skipped-especially under Nassau County conditions where freeze-thaw, coastal moisture, and those sudden winter gusts make every detail matter. Right now, I’m breaking the whole install into three big phases: prepping your deck and protecting those edges so water can’t sneak in, laying out reference lines that keep everything straight from the sidewalk, and then locking the metal shingle system together with flashing, fasteners, and finishing details that make the roof look sharp and stay tight for decades.

Why These Three Phases Matter in Nassau County

When you think about how many older capes, colonials, and raised ranches are sitting on this island-roofs that were framed back when lumber was drier and fasteners were heavier-you realize pretty quickly that every one of those structures has decking that’s been through at least twenty humid summers and cold, salty winters. So the three phases I just outlined aren’t just a neat framework; they’re a safety net. Your prep phase keeps you from building on top of rot or ripples. Your layout phase guarantees that the dimensional profile looks clean and professional instead of crooked and rushed. And your locking phase is where you actually create the weather-tight system that justifies switching to metal shingles in the first place.

Drive through Valley Stream or Garden City and you’ll spot plenty of 1960s colonials where the deck underneath is a mix of original solid boards and 1980s patches-those patches tend to sit a little proud or a little low, so if you skip careful prep, your metal shingle courses will telegraph every wobble. Over in Merrick or parts of Long Beach, older decking near the coast often holds extra moisture in the grain even when it’s not visibly soft, which means you need underlayment that breathes a bit and drip edges that shed salt air without corroding. Basically, Nassau County isn’t a lab; it’s a testing ground, and the three-phase approach gives you room to handle each quirk in order.

Deck Inspection and Fixing Soft Spots Before Anything Else

Before a single roll of underlayment gets opened, I walk the entire deck with a hammer and a clipboard. Tap every third rafter bay. Listen for a hollow thunk or watch for bounce. If the OSB or plywood flexes more than a quarter inch, mark it with chalk and pop the section out once the old shingles are stripped. Sometimes you’ll find a two-foot square of mush where a gutter overflow sat for years, and that square will be right where a valley channel dumps water-fixing it now costs you maybe forty dollars and an hour; ignoring it costs you a callback and a stained ceiling below. Don’t skip this.

Phase One – Prep the Deck and Protect the Edges

On most Nassau County colonials I work on, the deck is a patchwork-half original tongue-and-groove boards from the fifties, half newer plywood or OSB from a reroofing job someone did in the nineties. If those seams aren’t level, you’ll see bumps telegraphing through the metal shingles, especially when sunlight rakes across the roof at six in the evening. So after you’ve marked and replaced any soft spots, take a long straightedge and check every seam where old meets new. If there’s more than a quarter-inch step, either sand it down or sister a strip of half-inch plywood across the high side to ramp it smooth. It sounds tedious, but picture what it looks like from the sidewalk: one wavy course of metal shingles announces “rush job” louder than a hand-painted sign.

Next comes underlayment, and here’s where a lot of crews phone it in because they figure metal shingles are so weather-tight the underlayment is just backup. Wrong. In Nassau County you’re dealing with ice dams on north-facing slopes, wind-driven rain from nor’easters, and that weird salty condensation that creeps into attic spaces near the water. I use a synthetic underlayment with a slip-resistant coating so my boots don’t slide when the roof is steep and damp. Roll it horizontally, starting at the eave, and overlap each course by at least four inches-six if the pitch is under 4:12. Fasten the top edge with cap nails or staples every twelve inches, and make sure every vertical seam gets a six-inch overlap as well. You want no gaps where wind can lift the edge or water can wick sideways.

Here’s the part almost everyone rushes through-and shouldn’t: drip edge and starter metal. Drip edge goes on before the underlayment at the eaves and after the underlayment at the rakes, and that sequence matters because it controls how water exits. At the eave, the drip edge sits directly on the deck, then you roll underlayment over it so any moisture that gets under the shingles drains onto the metal and out to the gutter. At the rake, the underlayment goes down first, then the drip edge caps it so wind-blown rain can’t curl back under the edge. In Nassau County, where coastal gusts hit forty miles per hour on a bad day, getting this backwards means you’ll see water stains on the fascia within two winters. I also add a starter strip-either a pre-bent metal starter or a cut piece of the same metal shingle material-along the eave to give that first full course something solid to lock into. Without it, the bottom edge can lift or rattle every time the wind picks up.

One more prep detail I never skip: valley underlayment. If your roof has an open or closed valley-most Nassau colonials do, especially the ones with attached garages or dormers-lay an extra eighteen-inch-wide strip of underlayment down the center of the valley before you run your field underlayment. That strip sits directly on the deck, then your main underlayment overlaps it on both sides by at least six inches. This double layer catches any water that funnels down the valley seam, and it buys you insurance if a fastener ever pops or a seam opens. I learned this habit working on a ranch in East Meadow where the valley had zero extra protection and the homeowner’s living room ceiling showed a brown stain every March when the snow melted fast.

Phase Two – Layout That Keeps Lines Straight from the Sidewalk

Picture a straight chalk line from ridge to gutter: that’s your vertical reference, and it’s the difference between a roof that looks professionally installed and one that looks like it was eyeballed in a hurry. Before you set a single metal shingle, snap a line from the peak straight down to the eave, centered on the roof plane or aligned with a dormer edge or chimney-anywhere that gives you a plumb, true reference. Then measure out from that line in both directions at the top, middle, and bottom of the slope, marking equal intervals that match the width of your metal shingles plus their designed overlap. If those marks don’t line up perfectly at all three points, your roof deck isn’t square, and you’ll need to cheat the layout slightly so the courses run parallel to the ridge even if they’re not perfectly perpendicular to the rake. It’s better to have a tiny taper at one edge than to have every course look crooked when someone stands at the curb.

On a windy November in Seaford, I re-roofed a 1950s cape where the old asphalt shingles had been nailed so inconsistently that the whole surface rippled-some courses were six inches to weather, others were four, and the result was a wavy mess you could see from two blocks away. The deck underneath was actually solid, just covered in a chaotic shingle pattern. So I used that job to refine my “string line every third course” technique for metal shingles. I’d snap a horizontal chalk line across the roof at the height of the third course, then another at the sixth, then the ninth, and so on, all the way to the ridge. As I installed each course, I’d check it against the nearest string line to make sure I wasn’t drifting up or down. By the time I hit the ridge, every course was dead parallel, and the dimensional profile looked tight and professional even though the deck underneath wasn’t perfect. That string-line habit is now part of every Nassau County install I do, especially on older homes where you can’t trust the existing eave or ridge to be level.

Working around dormers and chimneys is where layout patience really pays off. Measure from your vertical reference line to the edge of the obstruction, then mark where each metal shingle course will need to be cut or notched. Don’t guess-use a tape and a level, and transfer those marks to the shingles before you’re up on the roof wrestling them into place. Picture the finished roof from the sidewalk. Picture each course lining up with the dormer sides so it looks intentional. Picture the way shadow and light will hit the dimensional profile at different times of day. If your cuts and your course lines don’t respect those visual anchors, the roof will look sloppy no matter how tight your fasteners are.

One trick I use on multi-plane roofs-like a colonial with a main gable and two shed dormers-is to start my layout at the most visible plane first, the one you see when you pull into the driveway. I get that section perfectly aligned, courses parallel to the ridge, cuts around windows clean, and then I work my way to the less visible planes, adjusting as needed so everything ties together at the hips or valleys. This way, if I have to fudge a course slightly to make a valley work, it happens on a back slope nobody looks at, and the front of the house stays crisp. It’s a small sequencing choice, but it’s the kind of thing that separates a layout hawk from someone just slapping panels up and hoping gravity holds them.

Phase Three – Locking Shingles, Flashing Details, and Finishing Clean

Once your starter row is bulletproof-locked onto the eave metal, fastened through the nailing flange, and checked for straightness-the next decision your hands have to make is where to drive fasteners on every subsequent course. Metal shingles typically have a raised profile on the visible part and a flat flange that gets covered by the next course, and that flange is where your screws or nails go. Use fasteners that are approved by the shingle manufacturer, usually stainless or coated screws with rubber washers that seal the hole. Drive them snug but not over-tight; if you crush the washer, you’ve created a leak point instead of sealing one. Space fasteners according to the install manual-often every twelve to sixteen inches along the flange-and make sure each one hits solid decking, not just underlayment or air.

During a humid July in Baldwin Harbor, I led an installation on a canal-front home where afternoon sea breezes made handling lightweight metal shingles tricky-those panels wanted to lift and twist the moment you set them down, and if you didn’t have a second pair of hands or a weight holding them, they’d slide right off the roof. So I taught my crew a specific staging pattern: we worked in narrower sections, maybe six feet wide at a time, moving from the leeward side of the roof (where the wind was blocked by the house) toward the windward side where the breeze hit hardest. We also adjusted our fastening sequence, driving at least two fasteners into each shingle immediately after aligning it, before we moved to the next one. That way the panels didn’t “oil can”-that wavy, flexing look you get when thin metal isn’t secured properly-and they didn’t lift while we were still getting the interlock pattern right. It added maybe twenty minutes to the job, but the finished roof looked tight and the dimensional profile held its shape even when the wind picked up later that week.

Now let’s talk valleys and ridges, because that’s where a lot of installs fall apart.

For valleys, you have two main options: open metal valley with a W-shaped channel, or a closed valley where the metal shingles weave or overlap across the valley seam. I prefer open valleys in Nassau County because they shed debris better-leaves, pine needles, and ice don’t hang around as much, and water moves fast down the center channel. Install the valley flashing over your double underlayment, secure it with fasteners along the outer edges only (never down the center where water flows), and then trim each metal shingle course to fit the valley angle, leaving about a half-inch gap on each side so the shingles don’t touch the valley metal directly. That gap prevents capillary action-water creeping between two touching surfaces-and it looks sharp. For ridges, use pre-formed ridge cap pieces that match your metal shingle profile. Start at one end, overlap each piece by the amount the manufacturer specifies (usually four to six inches), and fasten through the upper flange into the ridge board. Make sure the caps sit evenly on both sides of the peak; if one side is lower, it’ll look crooked from the street and it might let wind get under the edge.

Cold-Weather Details and the Port Washington Checklist

Back on a frigid January job in Port Washington, I discovered that a previous roofer had skipped proper starter and drip edge details on a north-facing slope-probably because his hands were frozen and he just wanted to finish. When the snow melted that spring, water backed up under the first course, found a gap in the underlayment where it wasn’t overlapped correctly, and dripped into the soffit. The homeowner called me to fix it, and I ended up stripping the bottom three courses, adding the missing drip edge and starter strip, re-lapping the underlayment with the six-inch overlap I mentioned earlier, and reinstalling the metal shingles with proper fastening. It took half a day, but it solved the problem permanently. From that job forward, I built a personal checklist: eave drip edge before underlayment, rake drip edge after, starter strip with at least two fasteners per shingle width, and an extra inspection walk along the eaves before I move up the roof. Cold weather makes every mistake more obvious because ice finds the path of least resistance, so if you rush through edge details in winter, you’ll pay for it in spring.

Common Shortcuts in Nassau County-and How to Spot Them

If you only have the patience for one “perfect” step, make it this one: layout. I’ve seen crews install gorgeous metal shingles with excellent fastening, proper flashing, and high-quality materials, but because they didn’t take the time to snap reference lines and check course alignment, the finished roof looked like it was installed by someone who’d had three cups of coffee and no level. Layout is more important than any fancy shingle style or premium coating, because if the lines are crooked, nobody’s going to care how reflective your finish is or how long the warranty lasts-they’re just going to see a roof that looks wrong. So before you hire a crew or tackle this yourself, ask: are you snapping vertical and horizontal lines? Are you using a string line or laser to keep courses parallel? Are you checking alignment from the sidewalk at least twice during the install? If the answer to any of those is no, you’re cutting a corner that’ll haunt you every time you pull into the driveway.

Other common shortcuts I see around Nassau: skipping valley underlayment to save ten minutes, using regular roofing nails instead of the coated screws that actually seal the hole, over-driving fasteners so the metal puckers, and failing to stagger seams on multi-width shingle systems. Every one of those habits looks fine on install day, but within two or three years you’ll see rust streaks, lifted edges, or water stains in the attic. The beauty of a metal shingle system is that it’s engineered to lock together and shed water for thirty or forty years with almost no maintenance-but only if you respect the engineering. Rush it, skip steps, or eyeball the layout, and you turn a premium roofing system into an expensive mess.

Why TWI Roofing Follows the Full Sequence

We’ve spent years working on Nassau County homes-capes in Seaford, colonials in Baldwin Harbor, raised ranches near the water in Port Washington-and every one of those jobs taught us something about what works and what fails when you’re dealing with freeze-thaw cycles, coastal salt air, and roofs that get pounded by sun, wind, and ice within the same month. That’s why TWI Roofing breaks every metal shingle install into the three phases I’ve outlined here: prep that handles the real condition of your deck and edges, layout that keeps the dimensional profile looking straight and intentional from any angle, and a locking-and-flashing sequence that respects both the manufacturer’s engineering and Nassau County’s weather extremes.

If you’re thinking about switching to a metal shingle system, or if you just want to understand what a proper install looks like so you can hold your contractor accountable, use this guide as your mental blueprint. Walk around your house and picture where each phase happens-where the drip edge sits, where the chalk lines get snapped, where the valleys and ridges need extra attention. Ask questions. Check the details. And remember that a dimensional metal shingle roof isn’t just a product you bolt on; it’s a system that only works when every piece is placed, fastened, and aligned with the kind of precision that makes the roof look like it grew there instead of being rushed into place. That’s the standard TWI Roofing holds ourselves to, and it’s the standard you should expect from any crew working on your Nassau County home.

One last thing: if you’re out there on a ladder looking up at your roof and thinking, “I can see a crooked line but I’m not sure if it’s the shingles or the house settling,” trust your eyes. Roofs should look straight, clean, and intentional, even on older homes that have shifted a bit over the decades. A good metal shingle install hides those imperfections through careful layout and alignment, so the final dimensional profile reads as crisp and new no matter what’s underneath. That’s the whole point of this guide-to give you the knowledge to recognize quality work, whether you’re doing it yourself or hiring someone like us to handle it, and to understand that every step in the sequence exists for a reason rooted in real Nassau County conditions, not just theory or habit.