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Cavity Wall Weep Hole Spacing Calculator

Estimate the number of weep holes needed along the base of a brick veneer or cavity wall.

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
32.81 ft
Schematic, drawn to the proportions you entered — not to scale on screen.

Weep holes needed

18 weep holes

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Also place additional weep holes at the ends of the wall, above openings (doors/windows), and at any other flashing discontinuity, beyond the uniform spacing counted here.

For the dimensions entered, expect a weep holes needed of 18. Note that wall length sits at the low end of the range this calculator was checked against, so treat the output as indicative rather than settled. Moderate confidence — sound arithmetic, but allow for the variation any real site introduces. Set for United States against IRC 2024. The market selector changes both the units and the code cited.

Add the equipment this sizes

This result is a specification — 18 weep holes — not a quantity. Put the thing it sizes into your project: how many, what you call it, and your supplier’s price.

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

  • Standard cavity/veneer wall practice places weep holes at regular spacing along the wall base directly above flashing, typically every 16-33 in (400-850mm) on-center depending on the weep hole type

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Frequently asked questions

Why do cavity walls need weep holes?
Water that gets past the brick veneer collects on the flashing at the base of the cavity — weep holes let that water drain out instead of accumulating and potentially causing efflorescence, freeze-thaw damage, or interior moisture problems.
What types of weep holes are common?
Open head joints (simplest, just an unfilled vertical mortar joint), plastic or mesh weep vents (better pest resistance), and wick/rope weeps (draw water out by capillary action) — spacing requirements vary somewhat by type.
Do weep holes need to align with the cavity drainage mat?
Ideally yes — weep holes should be positioned so they connect directly to the drainage path created by any cavity drainage mat or mesh, not blocked by mortar droppings or other debris.