Counter Flashing Calculator

Measurement tab: Enter the total linear footage of counter flashing needed. For chimneys, this is typically the two side lengths where step flashing runs (the front apron and rear cricket flashing are separate components). For sidewalls, this is the full wall length. Select the mounting method — reglet (groove cut into mortar joint) is the gold standard for masonry, surface-mounted is used for stucco, and existing reglet applies when replacing old counter flashing in an already-cut groove. Count all corners where the counter flashing changes direction, as corners require custom bending and add cost.

Material tab: Choose between lead (traditional, most conformable), aluminum (modern standard, corrosion-free), copper (premium, longest life), and galvanized steel (economical). Select the profile width — 4 inches is standard with 1 inch in the reglet and 3 inches of apron overlapping the step flashing below. A 5-inch profile provides extra overlap for high-wind or heavy-rain areas. Match the counter flashing material to the step flashing material below to prevent galvanic corrosion between dissimilar metals.

Cost tab: Reglet grinding is the single largest labor component for new installations — diamond blade cuts into mortar joints cost $3-$6 per linear foot depending on mortar hardness. Sealant in the reglet is critical and should be polyurethane or tri-polymer for long-term flexibility. A professional roofer handles most counter flashing installations at $8-$15 per linear foot; a mason is preferred for complex stone walls or when the reglet work requires special care around historic masonry.