How Weep Holes Drain Water From Masonry Walls

Brick and other masonry veneer can admit some water through joints or materials. A drainage cavity and flashing direct that water back out before it reaches the building’s interior. Weep holes are the outlet openings that let water escape at the bottom of the cavity and above horizontal interruptions such as shelf angles or lintels where flashing collects water.

The drainage path is a system

Water must be able to travel from the back of the veneer to the flashing, then through the weep opening to the exterior. A weep hole without properly lapped flashing may not collect the water. Flashing that slopes the wrong way, has open end dams, or is punctured by fasteners can direct water into the wall. The water-resistive barrier and flashing laps must follow the approved detail.

Keep outlets open

Mortar droppings, debris, sealant, paint, or landscaping can block weep openings. Use the specified weep materials and installation method, and protect the drainage cavity during masonry work. Do not fill the opening for appearance or assume that face-sealed masonry eliminates the need for drainage unless the wall design specifically provides another approved system.

Where they matter

Weeps are commonly placed at the base of veneer walls and above flashing at openings and structural ledges. Exact spacing and construction depend on the applicable code, wall system, project documents, and manufacturer’s instructions. Confirm the detail before laying units because adding an opening later may not repair missing or improperly lapped flashing.

Field inspection checklist

• Locate weeps at the flashing line shown on the drawings.
• Verify flashing laps, corners, and end dams direct water outward.
• Keep the cavity free of mortar bridges and debris.
• Check that weep openings remain visible and unobstructed after finishes and grading.
• Coordinate spacing and material with code and project details.

Trace water from entry to exit

Masonry veneer is not assumed to be perfectly watertight. Rain that passes the outer wythe should encounter a drainage cavity, reach flashing and drain through weep openings to the exterior. The water-resistive barrier behind the cavity protects the backing; flashing directs water outward at interruptions such as shelf angles, lintels, foundations and roof intersections.

Weep holes work only if the cavity is clear and the flashing is continuous, sloped or otherwise detailed to drain. Mortar droppings, insulation, insect screens installed incorrectly or sealant can block the outlet. A row of open head joints at the base cannot compensate for missing or reverse-lapped flashing.

Use the code detail for the right wall type

The adopted code may prescribe weep spacing and opening dimensions for specific residential veneer conditions; commercial assemblies may rely on other code sections, approved details and project specifications. Do not transfer one prescriptive spacing to every façade. Verify the local edition and amendments, wall construction, cavity, flashing location and whether the veneer is anchored or adhered.

At shelf angles and lintels, drainage must cross the support and discharge past the face. At window and door heads, end dams or other flashing details may be needed to prevent water from running into the wall ends. Coordinate the weep location with the flashing and cavity drainage material before masonry is laid.

Prevent blockage during construction

Keep mortar from bridging the drainage cavity. Use a cavity-management method compatible with the design, and inspect the base and interruptions before they are covered. Protect flashing from punctures and verify laps direct water outward. Weeps should be installed in the locations shown and remain open after tooling and cleanup.

If a weep is blocked, clear it without damaging the flashing or water-resistive barrier. Repeated wetting, staining or efflorescence below an opening can signal a drainage or flashing defect. Investigate the path of water rather than merely drilling additional holes through the veneer.

Check the whole wall envelope

Inspect transition details at windows, parapets, roof edges, grade, balconies and changes in cladding. Confirm that the cavity is drained and ventilated as designed, but do not assume every cavity uses identical ventilation openings. The air space must remain within the required geometry and must not become a conduit for fire or pests contrary to the code detail.

For the exam, describe weeps as the outlet in a larger drainage system. Cite the project’s adopted code, approved assembly and manufacturer details; an ICC model code edition is not automatically enforceable in every jurisdiction.

Example: water appears below a lintel

If staining appears below a lintel after rain, check whether flashing is present, continuous and turned up at its ends; whether the cavity is clear; and whether weep outlets remain open. A row of weeps below the lintel cannot drain water if the flashing is missing or slopes inward. Remove a small amount of mortar only under an approved investigation plan so the concealed layers are not damaged.

Trace the route from the wall face to the backing: check sealant joints, window-head flashing, end dams, cavity insulation and the water-resistive barrier. Record moisture conditions and repair the entry path, not just the stain. The repair detail should preserve veneer anchorage, fire blocking where required and drainage to the exterior.

Pre-close-in quality review

Inspect flashing before it is concealed: check laps, end conditions, support, termination and the route to each outlet. Confirm the drainage cavity is free of mortar droppings and that weep openings are spaced and sized as the approved code detail requires. Photograph shelf-angle and lintel conditions for the closeout file.

After installation, recheck the outlets and remove mortar smears or sealant that block them. If the wall leaks, evaluate the water path and flashing continuity rather than adding holes without a drainage plan.

Key takeaway

Weep holes are the drainage outlet, not a substitute for flashing. Preserve the full path—cavity, flashing, and clear exterior opening—to manage water behind masonry veneer.