Construction glossary · Envelope and finishes
What is flashing in construction?
Flashing is the sheet metal or membrane material installed at joints, transitions, and penetrations in a building envelope to direct water away from the assembly and shed it to the exterior. On a commercial job it shows up as base flashing, counter flashing, step flashing, through-wall flashing, and cap flashing, each detailed at a specific intersection. The estimator takes it off in linear feet by type, since the stock, gauge, and labor differ for each.
Updated June 2026 · Reviewed by the Ruh construction team
Flashing locations on a building
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Book a walkthroughIn US commercial construction, flashing is the formed metal or flexible membrane that bridges a discontinuity in the envelope and keeps water out of the wall or roof assembly. The trade distinguishes it by location and function: base flashing turns up at a roof-to-wall intersection, counter flashing laps over the base and is let into a reglet or under the cladding, step flashing weaves into a sloped roof against a wall, through-wall flashing collects water inside a masonry cavity and drains it to weeps, and cap flashing tops a parapet. Material matters for pricing. Galvanized steel, prefinished aluminum, copper, and stainless each carry different unit costs, and gauge or weight (for example 24 ga vs 26 ga) drives the number. As an estimator you read the wall sections and roof details, identify each flashing condition, and quantify it in linear feet against the price book for that profile. Miss a counter flashing run and the assembly leaks; the detail, not the plan, governs the count.
Flashing is quantified in linear feet (lf) by type and profile, with separate line items for base, counter, step, through-wall, cap, and edge metal. You pull it from the wall sections, roof plans, parapet details, and exterior elevations, scaling each run along the intersection it protects. Penetrations (curbs, pipes, scuppers) are counted as each, then converted to lf of girth where the detail calls for field-formed pans. Material, gauge or thickness, and finish are recorded per run because they change the unit price. Waste and lap allowance (commonly a few percent for overlaps and corners) is added on top of the measured length.
Worked example
Take a 30 ft wall-to-roof intersection on a single-story commercial building, detailed with both step flashing at the roof line and counter flashing let into the wall above. Step flashing runs the full 30 ft, so that is 30 lf. Counter flashing laps over it for the same run, another 30 lf, giving 60 lf of formed metal before allowances. Add 5 percent for laps and corner overlaps: 60 lf x 1.05 = 63 lf. Price 24 ga prefinished metal at an illustrative US installed rate of 12 dollars per lf (material plus labor): 63 lf x 12 dollars = 756 dollars for that intersection. If the spec bumps to a heavier gauge at 15 dollars per lf, the same 63 lf reads 945 dollars. Two numbers, one detail, and the gauge call drives a 189 dollar swing on a single 30 ft run.
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How Ruh handles flashing
Ruh reads the wall sections, roof details, and elevations, identifies each flashing condition by type, and measures the runs in linear feet, splitting base, counter, step, and through-wall into separate line items with the gauge and finish noted. It then prices each run on your own price book, including lap and corner allowance, and presents the takeoff for the estimator to review against the details and sign off.
See construction estimating softwareFlashing: frequently asked questions
Why split flashing into separate line items instead of one lump linear-foot number?+
Because the material, gauge, profile, and labor differ. Step flashing woven into shingles, through-wall flashing with weeps, and a parapet cap are different installs at different unit costs, so a single blended number hides risk and misprices the work.
Do I count counter flashing and base flashing as one run or two?+
Two. They occupy the same intersection but are separate pieces of metal installed in separate operations, so you carry the linear footage twice, once for each profile, even when they share a length.
How much waste should I add to flashing lengths?+
A small lap and corner allowance, commonly a few percent, on top of the measured run. Tight inside and outside corners and the lap at each joint consume stock beyond the net dimension scaled off the detail.
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Figures on this page are illustrative. Construction estimates depend on project-specific conditions, source documents, market pricing, and professional judgment. Ruh's AI assists the estimator and does not replace professional review: your team reviews, validates, and approves every estimate, bid, and pricing decision.