What is the most common cause of roof leaks?

Improper or deteriorated flashing accounts for the majority of roof leaks, especially around chimneys, walls, and penetrations.

Aluminum or galvanized flashing?

Aluminum is easier to work with and does not rust. Galvanized is stronger but can corrode over time. Copper is premium and lasts longest.

How often should flashing be inspected?

Annually. Check for lifted edges, cracked sealant, rust spots, and gaps. Address issues immediately to prevent leaks.

Roof FlashingGenerating image…

Roofing

Flashing

$0.50-$5 per linear foot depending on material

Roof Flashing: Sealing Roof Joints & Penetrations (2026)

Prepared by Lumberama's Building Materials Team

|Last updated May 15, 2026|Sources & methodology

Roof flashing is sheet metal formed and installed at roof transitions, penetrations, and intersections to direct water away from vulnerable joints. Proper flashing is the most critical factor in preventing roof leaks. Types include step flashing, counter flashing, valley flashing, and vent pipe boots.

Key Features

Seals vulnerable roof joints; Multiple types for each application; Aluminum
galvanized
or copper; Pre-formed and field-bent options; Prevents the majority of roof leaks

Specifications

Step flashing: 4x5 in pieces. Valley flashing: 20 in wide rolls. Material gauges: aluminum 0.019 in

galvanized 26 gauge

copper 16 oz. Available in rolls or pre-cut pieces.

Applications

Chimney-to-roof joints; Wall-to-roof intersections; Roof valleys; Vent pipe penetrations; Skylight perimeters

Installation Overview

Step flashing is woven into shingle courses at walls. Counter flashing is embedded in mortar joints over step flashing. Valley flashing is laid before shingles with proper overlap. Vent boots slip over pipes and seal with roofing cement.

Pros & Cons

Pros

✓ Prevents most roof leaks; Long-lasting when properly installed; Multiple material options; Copper adds aesthetic value; Field-adjustable

Cons

✗ Requires skilled installation; Incorrect flashing is the top leak source; Copper is expensive; Must integrate with roofing sequence; Sealant maintenance needed

Top Brands

Amerimax

Oatey

Quarrix

Spectra Metals

Code Requirements

Required per IRC R903.2 at all wall-to-roof intersections, penetrations, and direction changes. Must be corrosion-resistant. Step and counter flashing required at chimneys per IRC R1003.20.

Buying Tips

Buy pre-bent step flashing pieces to save time. Copper flashing is worth the investment at chimneys for longevity. Keep roofing cement on hand for sealing edges.