Steep-Slope Flashing Installation: Drip-Edge, Valley, Step, and Counter

Why Flashing Sequence Is Everything

Water runs downhill. Every flashing detail on a steep-slope roof is designed around that single fact. Install a piece in the wrong order and you create a pocket that channels water under the system instead of off it. The four flashing types you will install today — drip-edge, valley, step, and counter — each protect a different transition, and each depends on the others being in the right place first.

Drip-Edge: Eave Before, Rake After

Drip-edge is an L-shaped metal strip (typically aluminum) nailed along the roof perimeter to direct water off the deck and away from the fascia. The sequence rule is firm and non-negotiable:

• Eave drip-edge goes down before the underlayment. The underlayment then laps over the top of the eave drip-edge. This way, any water that works under the first course of shingles is kicked out over the gutter.
• Rake drip-edge goes on after the underlayment. The underlayment tucks under the rake drip-edge so wind-driven rain that hits the edge is shed onto the underlayment, not behind it.

Fasten drip-edge with roofing nails spaced according to the manufacturer's specification — generally every 8 to 12 inches along the hem, placed high enough that fasteners are covered by the next course of material. Lap end joints in the direction of water flow (upper piece over lower piece) by a minimum typically stated by the manufacturer, often at least 2 inches.

Valley Flashing: Open-Valley W-Metal

A valley is where two roof planes meet at an inside angle. Water volume is highest here. A W-valley (also called W-metal) is a pre-formed 26-gauge galvanized sheet with a raised center rib that separates the two water channels and prevents turbulence from one plane crossing to the other.

Key installation points:

• Center the W-metal in the valley; the center rib must align with the valley centerline.
• Secure with clips or fasteners placed at the edges of the flashing only — never nail through the water channel.
• Lap upper sections over lower sections by the manufacturer's specified amount (commonly 6 inches or more) and seal the overlap.
• Install end-dams at the eave to prevent water from shooting off the bottom edge under the drip-edge.
• Keep shingles trimmed back from the center rib by the distance shown in the manufacturer's detail, and apply a bead of urethane sealant along the shingle cut edge to close the gap.

For a closed or woven valley, shingles instead of exposed metal cover the valley, but a mineral-surface cap sheet or membrane underlayment still runs the full length beneath. The principles of sequencing — lower courses first, no exposed fasteners in the channel — remain the same.

Step Flashing: Shingle and Metal, Course by Course

Step flashing protects the joint between a sloped roof surface and a vertical sidewall or chimney. Each step-flashing unit is an individual bent piece of metal (typically aluminum, at least as wide as one shingle exposure and tall enough to turn up the wall several inches — commonly 4 inches horizontal by 4 inches vertical after bending, though dimensions vary by manufacturer and local practice).

The installation alternates: lay a shingle course, set a step-flashing unit on top of that shingle and tight to the wall, nail the flashing unit to the deck only (one nail, high on the flange, covered by the next shingle), then lay the next shingle course over the horizontal leg of the flashing. Each piece overlaps the one below by at least the shingle exposure so no gap is exposed to weather. Never caulk the top edge of step flashing to the wall — that joint must remain open so the counter flashing can do its job.

Counter Flashing: Locking the Top Edge

Counter flashing is the cap that covers the top turned-up edge of the step flashing (or base flashing at a chimney). A two-piece system allows for thermal movement: the reglet piece is embedded in a saw-cut slot (called a reglet) in the masonry, and the cap piece hooks over it and laps down to cover the step-flashing leg.

• Saw the reglet horizontally into the mortar joint or masonry block to the depth required by the manufacturer (commonly about ¾ inch).
• Clean the slot of dust and debris.
• Insert the reglet receiver and secure it.
• Hook the cap counter flashing over the reglet and press it down over the step-flashing leg.
• Seal the top of the reglet with urethane roofing sealant — this is the only sealant joint; the bottom of the counter flashing must remain free to allow drainage.

Safety on the Mock-Up and the Real Roof

Even on a low-pitch mock-up, treat every work platform as a fall hazard. Wear slip-resistant footwear and keep the deck clear of scrap metal and nail drops. When operating a pneumatic nailer, keep the nozzle pointed away from yourself and your partner and engage the safety tip fully before each shot. Eye protection is required whenever cutting metal flashing — aluminum and galvanized steel create sharp burrs and chips. Wear cut-resistant gloves when bending or handling sheet metal edges. Urethane sealant is an irritant; nitrile gloves protect your skin during application.

The Inspection Mindset

Professional roofers inspect their own work before the next course covers it — because once shingles go down, every deficiency is either hidden until it leaks or expensive to uncover. Use the checklist not as a final hurdle but as a real-time guide. If you cannot see the lap, measure it before you nail. If you cannot confirm sealant continuity, run the bead before the flashing goes flat.