Retrofit weep holes and vents into an existing masonry cavity wall with a moisture problem

Steps

1. Diagnose the moisture problem first (interior staining, base-of-wall efflorescence, trapped water found during invasive investigation) to confirm inadequate or blocked weeps/vents are a contributing cause.
2. Locate the existing cavity and any existing weep holes/vents, and check whether they are blocked by mortar droppings and debris, or were never installed, which is common in older cavity wall construction.
3. Retrofit weep holes at the base of the cavity (typically at head joints, above flashing) and provide vents near the top of the wall, with spacing set by the mason/engineer for the specific wall height and cavity condition.
4. Clear mortar droppings and debris from the base of the cavity where feasible (cavity vacuum, cleanout, or selective brick removal), since new weep holes won't function if the cavity floor is blocked.
5. Verify flashing is present and properly lapped at the base of the cavity where new weeps are installed, since a weep without functioning flashing behind it won't drain the cavity.