Masonry Magazine June 1993 Page. 21
Vents
Weepholes serve a dual function as water drainage locations and vents. Vents are desirable in masonry to help reduce the moisture content of the masonry during drying periods. Aircirculation through the voids within the masonry promotes equalization of moisture content throughout the masonry and walls become uniformly dried.
Vents are considered especially desirable where air is confined within masonry, such as in parapets.
MAINTENANCE
Maintenance programs should involve maintaining the "as-built" design documents, records pertaining to inspections during the service life of the structure, and continuing appraisal of the performance of the structure. Documentation of inspections, if efflorescence and water stains are observed, and logs of reported water penetration at identified locations, assist in determining proper corrective actions.
Knowledge of the wall design and construction will influence repair decisions. Construction omission of flashings and weepholes may be completely rectified by removing units and installing new flashings and weepholes. However, this may prove to be a costly and extremely time consuming method.
Alternatively, and as a more economical procedure, weepholes and vents may be drilled throughout the wall system to promote drainage and drying. Weepholes so drilled should be either at the intersection of the bed and head joints or into the cores at the bottom of the wall. Vents should be drilled at the top of the wall or directly below bond beams.
DETAILS
Cavity Walls
As illustrated in Figure 1, the flashing in a cavity wall should extend from the midpoint of the inner faceshell across the unit surface, project downward to the foundation surface, outward to the exterior face of the wall, and terminate with a sloped drip. Weepholes should be located at a maximum of 32 inches apart.
Flashing at Bond Beams
Flashings at bond beam locations, like their cavity wall counterparts, should be positioned to direct water to the exterior. Care should be exercised to ensure that grout in the bond beam is level with the surface of the units. If not, mortar should be applied in this area to cause a downward slope of the flashing to the exterior.
Although not shown, vents can be installed in the vertical head joints or into the cores of the masonry units immediately below the bond beam.
This detail may be modified for single wythe construction. Filling the cores in the first course below the flashing (shown as a bond beam in Figure 2) with gravel or other similar material will support the flashing from beneath and prevent sagging of the flashing and the formation of reservoirs on the flashing at the core locations.