Climate & geography
The climate conditions working on Imperial Beach buildings
Within three miles of the surf line, dwell time does the damage, not rainfall. These are the three conditions that keep coastal surfaces damp long enough to matter. Each one is matched to the housing stock described above.
The marine layer — May Gray and June Gloom
Cool ocean water chills the air above it and onshore flow pushes that layer over the coast overnight. Coastal morning relative humidity commonly sits at 80–90% for much of May through September. Because most coastal housing was built without air conditioning, indoor humidity simply follows it — so mold grows on cool surfaces with no leak involved.
Where it bites: Mission Beach, Ocean Beach, Pacific Beach, Imperial Beach, Coronado, La Jolla below 80 ft, the Del Mar Beach Colony
Atmospheric rivers, not steady rain
The county averages around ten inches a year, but it arrives in a handful of intense winter storms. A flashing defect does nothing for eight months, then takes two or three inches in a day driven sideways by wind. Every dormant envelope fault fails on the same afternoon.
Where it bites: County-wide, worst on west and south elevations and under heavy tree canopy
Lagoon and canyon air drainage
Carlsbad's three lagoons, the San Elijo and Buena Vista corridors and the county's canyon systems all drain saturated air inland and downhill overnight. A house two miles from the ocean in one of those corridors can run higher overnight humidity than a bluff-top house much closer to the water.
Where it bites: Carlsbad, lower Cardiff, Vista's creek valley, canyon-rim blocks in North Park, Clairemont and La Mesa