Metal Roof Flashing: Trim Pieces, Closures and Where They Go

A metal roof panel is almost impossible to leak through. The leaks show up at the edges, the peaks and anywhere the roof meets a wall, and those are exactly the spots covered by metal roof flashing. Each trim piece has one job: shed water off a seam or edge and send it back onto the face of the panels, where it can run freely to the gutter. Put a piece in the wrong order, or leave out the foam closure that fills the panel ribs, and wind-driven rain, snow and insects find their way into the roof deck.

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The short answer for most homeowners is that a complete metal roof uses six to eight flashing types: eave trim (or drip edge), rake or gable trim, ridge cap, sidewall flashing, endwall flashing, transition or pitch-change flashing, and valley flashing where two roof planes meet. Closure strips seal the gaps between those trims and the ribbed panel profile. Corrugated and standing seam roofs use the same basic map, but the shapes of the pieces and the way they fasten are different.

Knowing what each part does and where it sits helps you order the right trim, check a contractor’s work, or track down the source of a drip on an older tin roof.

How Metal Roof Flashing Works as a System

Every piece of metal roof flashing follows the same principle as shingles: the higher piece always laps over the lower one. Water moves downhill, so any joint where an upper piece tucks under a lower piece becomes a funnel straight into the building. Installers call this “shingling” the trim, and it applies to overlaps between trim lengths as well as between trim and panels.

The second principle is that flashing on a metal roof has to tolerate movement. Steel and aluminum panels expand and contract with temperature, sometimes by a quarter inch or more over a long run on a hot afternoon. Trim that is fastened rigidly through both the panel and the wall will eventually tear sealant or elongate screw holes. Good details let the panel slide under the trim, with fasteners placed in the high ribs or in the trim’s hem rather than locking everything together.

Third, the ribs themselves create voids. A corrugated steel panel has rounded waves, and a ribbed or standing seam panel has tall vertical legs. Wherever a flat trim piece crosses those ribs at the eave or ridge, there are open gaps. Closure strips, usually closed-cell foam cut to the exact panel profile, plug those gaps so wind cannot push rain and snow under the trim.

The Main Trim Pieces and Where Each One Goes

Eave trim or drip edge

Eave trim runs along the bottom edge of the roof, over the fascia. It is installed first, directly on the deck or on the underlayment’s lower edge, so the underlayment laps over it and the panels sit on top. Its kicked-out lower hem throws water past the fascia and into the gutter. On a roof with gutters, a gutter apron profile can serve the same purpose.

Rake or gable trim

Rake trim covers the sloped edges at the gable ends. It goes on after the panels, wrapping over the last rib or panel edge and down the face of the rake board. On standing seam roofs, the panel edge is often bent up and hooked into a cleat, and the rake trim snaps over it. On corrugated roofs, the trim is screwed through the high rib, never the flat valley of the panel.

Ridge cap

The ridge cap covers the peak where two roof planes meet. It sits on top of closure strips laid across the top ends of the panels. Vented ridge designs use a breathable profile closure instead of solid foam, so attic air can exit while rain stays out.

Hip cap

Hip caps cover the outside corners on hip roofs. They work like a ridge cap but run downhill, and they use cut closures or a flexible universal closure because the panel ends are angled.

Sidewall flashing

Sidewall flashing sits where a roof plane runs alongside a vertical wall, such as a dormer cheek or a second-story wall. One leg lies over the panel rib, the other runs up the wall behind the siding or under a counter flashing. Water running down the wall lands on the trim and travels down the slope.

Endwall flashing

Endwall flashing goes where the top of a roof plane dies into a wall, such as a shed roof against a house. It acts like half of a ridge cap: one leg extends down over the panels with a closure strip underneath, the other runs up the wall behind the siding.

Transition and pitch-change flashing

Where a steep slope breaks to a shallower one, such as a gambrel or a porch roof tied into a main roof, transition flashing bends at the same angle as the pitch change. The upper panels lap over it, and the lower panels slide under it, with closures on both sides.

Valley flashing

A valley is the inside corner where two planes meet. A wide W-shaped or open valley pan is installed on the deck first, often over a strip of self-adhering membrane, and panels are trimmed to leave a clear water channel down the center.

Corrugated vs Standing Seam: How the Details Differ

Corrugated roof flashing tends to be simpler and less expensive. Exposed-fastener panels are screwed directly through the face, and most trim is screwed through the high ribs with gasketed screws. Corrugated iron roof flashing on older barns and sheds is often hand-bent from flat sheet, and many leaks on those buildings trace back to rust at overlaps or missing closures rather than the panels.

Standing seam roofs hide their fasteners. Panels attach with clips under the seams, and the trim attaches to cleats or z-closures that are fastened to the panel, so the panel can still move. Trim profiles are usually custom bent on a brake to match the seam height. The result looks cleaner and lasts longer, but the flashing details take more skill and the trim costs more.

Closure Strips: The Small Part That Stops Big Leaks

Closure strips are often the piece people leave off, and they cause a surprising share of leak calls. There are two main kinds. Inside closures fit under the panel at the eave, matching the bottom of the ribs, so the panel sits on the eave trim with no gaps. Outside closures sit on top of the panel at the ridge, endwall and transition, matching the top of the ribs so the cap or flashing has a solid surface to seal against.

Each closure must match the exact panel profile. A closure made for a 7/8-inch corrugated wave will not seal a 1-inch ribbed panel. Order closures from the same source as the panels when possible, and confirm the profile name and rib spacing. Use a bead of butyl tape or sealant on both faces of the closure, and fasten through the closure into the high rib where the manufacturer allows.

Vented closures have small openings or a mesh face, so air can move while larger insects and wind-driven rain are blocked. They are used at ridges over vented attics. In heavy snow regions, solid closures are sometimes preferred at endwalls to stop powder snow from blowing in.

Order of Installation, Step by Step

Every roof layout is different, but the sequence for a typical gable roof with one sidewall looks like this:

1. Prep the deck. Replace damaged sheathing, then install underlayment. Use self-adhering membrane in valleys and at eaves in cold climates.
2. Install eave trim. Fasten it along the fascia with its top flange on the deck, overlapping lengths about 2 inches in the direction of water flow.
3. Install valley pans. Set them over a membrane strip, starting at the bottom and lapping each upper length over the lower one by at least 6 inches.
4. Set inside closures and panels. Lay a sealant strip on the eave trim, press the inside closures in place, then install the panels, square to the eave.
5. Add sidewall flashing as you go. Install it as the panels reach the wall, tucking the vertical leg behind the house wrap or siding.
6. Install rake trim. Cap the outside panel edge on each gable, working from the eave up so each upper piece laps over the lower piece.
7. Finish the top. Set outside closures across the ridge or endwall, then fasten the ridge cap or endwall flashing over them.

A complete metal roof trim kit from the panel supplier often bundles eave, rake and ridge pieces with matching closures, screws and touch-up paint. For a small shed or porch roof, a kit takes most of the guesswork out of ordering.

Ladder and Roof Safety

Metal panels are slick, especially with morning dew, frost or the thin film of oil left from the factory. Work on a dry day, wear soft-soled shoes with good grip, and use a personal fall arrest system with a properly anchored roof anchor on any slope steeper than about 4 in 12. Set extension ladders at a 4-to-1 angle (one foot out for every four feet up), extend them at least 3 feet past the roof edge, and tie them off at the top.

Carry trim and panels up with a helper or a hoist rather than climbing with long sheets in one hand. Wind catches metal like a sail. Cut edges are sharp, so wear cut-resistant gloves and eye protection. On any home with two or more stories, or on steep pitches, hire a professional roofer with scaffolding and fall protection rather than working from a ladder.

Troubleshooting Common Flashing Leaks

• Water at the eave or under the fascia: often missing inside closures, eave trim installed over the underlayment instead of under it, or short panel overhang.
• Drips along a sidewall: the vertical leg of the sidewall flashing is sitting on top of the siding instead of behind it, or the bottom end lacks a kick-out to divert water away from the wall.
• Leaks near the ridge: closures missing, cut to the wrong profile, or crushed by over-tightened screws.
• Rust streaks at laps: dissimilar metals in contact (copper and galvanized steel, for example) or bare cut edges. Use matching metals and touch-up paint on cuts.
• Loose or backed-out screws: thermal movement working them loose. Replace with the next size up gasketed screw rather than piling on sealant.

When tracking a leak, start uphill from where water appears. Water often travels along a rib or the underside of a trim piece several feet before it drips.

Typical Costs for Metal Roof Flashing

Trim prices vary by gauge, finish and whether pieces are stock or custom bent. Painted stock trim in 10-foot lengths generally costs a few dollars to the low teens per linear foot for common profiles. Custom brake-bent trim for standing seam roofs costs more, and bare galvanized pieces cost less. Foam closures are inexpensive, usually a couple of dollars per strip.

For a professional repair, replacing a section of failed flashing at a wall or ridge on a residential roof often runs a few hundred dollars, while reflashing an entire roof during a panel replacement is folded into the overall project cost. Because labor dominates, it pays to get flashing right the first time.

When to Call a Pro

Simple corrugated sheds, carports and porch roofs are reasonable DIY projects. Call a metal roofing contractor for standing seam work, chimney or skylight penetrations, valleys on a main house roof, low-slope transitions, and any roof two stories or higher. A pro will also know local requirements for underlayment, snow and wind uplift, and whether a permit is needed for a reroof in your area.