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Storefront Sill Flashing Calculator

Calculate the sill flashing needed for a storefront system's base, with waste allowance.

Computed in your browser — nothing you enter is uploaded. Figures are presented for United States against IRC 2024, and every formula is cited under regulatory standards below.

Last verified 2026-08-26 · v1.0.0

Market
Imperial · sales tax
82.02 ft
Schematic, drawn to the proportions you entered — not to scale on screen.
Who is doing the work?

Waste is set to 5% by hand. Pick a tier above to replace it, or keep your own figure.

Sill flashing needed

86.12 ft

High confidence

With the figures above, the sill flashing needed comes to 26.3 m. This is calculated for United States and cites IRC 2024. Building in another market? Change the selector above so the units and code reference follow.

Estimated cost — your price

This site holds no price list for this material — local prices vary too much to publish honestly. Enter your supplier's price and the result is costed with it.

Preliminary estimate, not certified engineering. This tool produces an indicative quantity calculation for planning purposes only — it is not a certified structural analysis, a guaranteed material takeoff, or a substitute for building department approval. Always verify measurements on-site and have a licensed contractor or structural engineer review any load-bearing, code-sensitive, or safety-critical work before purchasing materials or starting construction. Spotted an arithmetic or standards error? Report it to contact@craftquantities.com with your inputs — confirmed fixes become pinned regression tests.

[Schema Verified] Computed in alignment with American Concrete Institute (ACI 318-19) formulas and International Residential Code (IRC 2024) spatial boundaries.

Regulatory standards & verification citations

  • Total sill flashing = sill length × (1 + waste allowance)

Your workspace

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Frequently asked questions

Why do end dams matter so much?
Because without them the flashing is a channel open at both ends, and water that collects in it runs straight off the ends into the wall. An end dam turns the flashing into a tray. It is a small piece of metal and it is the difference between a sill that drains and a sill that irrigates the framing beside it.
Where should the weeps discharge?
To the outside face, through the cladding, above the finished level below. A weep that discharges into the cavity moves water from one part of the wall to another; a weep blocked by mortar droppings or sealant does not discharge at all. Both are common and both are found only when the wall starts staining.
Should the sill flashing be sealed at the front edge?
No — that is the drainage path. Sealing the leading edge is an intuitive-looking mistake that turns the flashing into a bathtub. The seal belongs at the back and ends, where water must not pass; the front is deliberately open so water can leave.
Does the flashing go under or over the water-resistive barrier?
Shingled so water always runs outward: the barrier above laps over the flashing's upstand, and the flashing laps over the cladding or barrier below. Reversing that lap at any point creates a path into the wall regardless of how much sealant is applied, and sealant is not a substitute for the correct lap order.