In San Diego, the major benefits of proper ventilation in a home are actually a twofold system. Regardless of the season, proper attic ventilation can help keep the inside temperatures comfortable for the homeowner. A buildup of heat settled in the attic causes the area to reach temperatures up to 140°F, which is a potential health hazard for occupants. Hot, moist air is a breeding ground for bacteria, mold, and other unpleasant particles that can affect people and the structure of the roof as well. Hot, moist air can be especially damaging to wood structures over time. Proper ventilation in attic areas allow moisture to be released without damaging wood, insulation, studs, and other materials.
In California, building codes require cross-ventilation — two openings to the outside that create a flow of fresh air through your attic. There should be at least 1 square foot of ventilation for every 150 square feet of attic space.
Fire resistant vents, vents made of corrosion resistant and non-combustible materials are recommended with mesh in size 1/4″ or less.
More information can be found here: https://ucanr.edu/sites/fire/Prepare/Building/Vents/
