Venting a rainscreen at the stucco weep screed

A homeowner in Southern California is building a stucco and stone wall with a rainscreen, a thin gap behind the siding that lets water drain and air move to dry out the wall. He asked whether he needs to drill vent holes at the bottom weep screed (the metal strip that lets trapped water escape at the base of stucco walls), whether he could skip venting entirely and just use the gap as a drainage layer since his climate is dry, and whether venting only the top without an open bottom would help.

A building science expert responded that venting only the top doesn't do much good on its own. The bottom of the gap still needs to stay open as a drainage path; otherwise water can pool there, and without an open bottom, air doesn't move well enough to carry moisture out the top either.

The expert also pointed out that in dry climates, the main value of a rainscreen gap is acting as a break that stops water from wicking through by capillary action, not necessarily its drainage or ventilation function. He suggested that for a reservoir cladding like stucco, which can hold and slowly release moisture after it gets wet, the homeowner's wall may need a different kind of moisture-management approach rather than a standard vented rainscreen. He didn't have a specific fix to offer, and the conversation was left open for others with more stucco-specific experience to weigh in.