Counter Flashing vs. Step Flashing: Specs, Sizes, and When You Need Both
Step flashing runs with the roof. Counter flashing caps it from the wall. They work as a system, not as alternatives. Here's how each piece functions, how to size them correctly on a quote, and why combining them the right way keeps water out without creating callbacks.
Step Flashing: What It Does and How It's Sized
Step flashing is installed at the intersection of a sloped roof and a vertical wall -- where a roof meets a dormer, adjacent wall, or chimney. Each piece is an individual L-shaped section of sheet metal installed with every course of roofing material. As each shingle course goes in, one step flashing piece goes in with it: flat on the roof deck and up the wall face, under the next shingle course.
The pieces don't connect to each other and there are no continuous seams. That's the design intent. Each piece handles water independently and the overlapping geometry sheds water downslope without relying on sealant.
IRC R905.2.8.3 sets the code minimum for asphalt shingle sidewall flashing at 4 inches in height and 4 inches in width, sized to direct water away from the wall and onto the roof or into a gutter. Most contractors run larger pieces than the minimum for cleaner reveals and longer service life -- typical fabricated sizes are 5 to 7 inches tall on the wall side and 7 to 10 inches long on the roof side. We fabricate step flashing in galvanized (G-90), prefinished steel (26 GA standard, 24 GA available), and aluminum (0.040"). Copper available on request.
Counter Flashing: Two-Piece and One-Piece Configurations
Counter flashing is installed over and around step flashing to cap the top of the flashing assembly against the wall surface. Where step flashing runs up alongside each roofing course, counter flashing is embedded into or surface-mounted to the vertical wall and laps down over the step flashing below.
Two-piece counter flashing.
The standard configuration for masonry and CMU walls. The upper section is inserted into a mortar joint or a cut reglet in the masonry and sealed in place. The lower section laps down over the step flashing, maintaining a gap between the roofing system and the wall system so each can move independently under thermal expansion and structural loads. Counter flashing is not mechanically fastened to the roofing system -- that separation is intentional.
One-piece counter flashing.
Used on frame walls with cladding that installs over the counter flashing. A single piece is embedded behind the cladding and laps down over the step flashing. Simpler installation, but the counter flashing must be tall enough to maintain a minimum 4-inch overlap over the step flashing after wall settlement and thermal movement.
Why the Assembly Requires Both
Step flashing is the primary water deflector. It handles every individual water path between roof and wall at each shingle course. Counter flashing is the cap: it covers the exposed top edges of the step flashing and the transition zone between the roofing waterproofing layer and the wall cladding, and it maintains a barrier against wind-driven rain getting behind the assembly from above.
The reason they aren't combined into a single piece is movement. A roof assembly and a wall assembly expand, contract, and settle at different rates and in different directions. A single rigid piece bridging both would eventually pull out fasteners, crack sealants, or open gaps as that movement accumulates over years. Two independent pieces, each fastened only to its own substrate, allow movement without compromising the seal at the transition.
Sizing to Spec on a Quote
Step Flashing
- Code minimum (IRC R905.2.8.3): 4" x 4"
- Common fabricated sizes: 5"-7" wall leg x 7"-10" roof leg
- Heavy-duty or high-wind: 6"-8" each leg
- Specify in pieces, not LF. Piece count equals one per shingle course.
Counter Flashing
- Surface-mounted on frame wall: 5"-8" face height, 2"-3" wall-embedded leg (typical fabricated dimensions)
- Reglet or masonry embed: 2" embed leg, 6"-8" exposed face (typical fabricated dimensions)
- Maintain at least a 3"-4" lap over the step flashing below; the larger overlap is preferred for high-wind exposure or stack-bond masonry.
Fastener and Sealant Notes
Step flashing is fastened to the wall only, not to the roof deck. One fastener per piece, high on the wall leg, so the bottom floats free with roof movement. No sealant is used between step flashing pieces. The overlap geometry is the water management method -- sealant here would interfere with drainage and eventually crack.
Counter flashing set in a masonry reglet is sealed with polyurethane or silicone at the embed joint. The face joint below the counter flashing -- between the counter flashing face and the step flashing -- is left open. That gap is intentional and allows drainage of any water that gets behind the assembly.
When to Call PDX Panels
We fabricate step flashing in quantity from contractor submittals. Send us your piece count, dimensions, gauge, and material. If you're working through leg lengths for a specific wall assembly or roofing system and aren't sure on the profile, call and we'll work through it with you.
Counter flashing profiles vary by wall type. We fabricate to architect specs, match existing in-place sections from a sample piece or field measurements, and fabricate standard reglet profiles from stock. Both step flashing and counter flashing qualify for same-day quotes. Call (503) 914-0210 or submit a request online.
Frequently Asked Questions
Can counter flashing be used without step flashing?
Not in a correctly detailed roof-to-wall transition on a steep-slope roof. Counter flashing alone has no way to handle the interface between individual shingle courses and the wall. Step flashing is the primary water barrier. Counter flashing caps the top of the assembly. Both are required by NRCA guidelines and most building codes for steep-slope applications at wall intersections.
What gauge should I specify for step flashing?
26-gauge galvanized (G-90) is standard for most steep-slope residential and commercial work. 24-gauge is available when additional stiffness is needed for longer pieces or high-wind exposure. Aluminum 0.040" is an alternative where galvanic corrosion with copper gutters or other dissimilar metals is a concern.
Do you fabricate reglet counter flashing for masonry walls?
Yes. We fabricate reglet-type counter flashing with a 90-degree embed leg and a stepped or sloped face section. Standard masonry reglet profiles, surface-mounted versions, and fully custom profiles are all available. Lead time is 3-5 business days from approved dimensions. Send us your profile sketch or field measurements and we'll confirm pricing before we cut.
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