Mention Southern California and most people think of warm sunny beaches, palm trees and a laid-back lifestyle. Mention the state in regards to construction and most consider California construction as no test for an assembly or detail. The phrase “that may work in California but won’t here,” is rather common. To a point, there is some truth to that claim.

Southern California does not have the heavy snow of Anchorage, the steady rain of Seattle or the brutal heat of Phoenix. But California has a seismic fault and we do get significant temperature swings. Our contractors must also overcome the built-in perception that since California is the Garden of Eden, our buildings are like our lifestyle—stress free. Even local contractors tend to forget that we can get temperature swings in relatively short periods of time.

In winter, Southern California frequently can warm to above 80 degrees Fahrenheit during the day. However, as soon as the sun sets, that temperature will drop and reach the low 40s. While you are chuckling that this temperature is nothing, it is still a 40 degree swing in degrees in less than 12 hours.

All building materials expand and contract with temperature swings and all areas have this issue, even in paradise. Materials can vary in the degree of movement, such as aluminum that has significantly more movement than cement. Slow swings in temperature place stress, fast swings in temperatures can place extra stress on the components of a building, thus resulting in cracks, joint separation or other perceived failures to blame on materials and installation.

Another and more relevant issue to those of us in Southern California is the humidity. While the swing in temperature is important, so is the swing in humidity. This is where few can compare to Southern California. The problem that is somewhat unique to Southern California is that a combination of temperature swings are combined with the humidity swings. This is most apparent on materials classified as hydrophilic. Hydrophilic means materials that can absorb moisture, such as drywall, plaster and wood.

Marine Layer

Here in movie land, we have what is known as the marine layer. This is a temperature inversion somewhat unique to California. The inversion or marine layer is created by warm land mass air being cooled by the cold waters of the Pacific Ocean. The cool air becomes denser than the warmer air above, and becomes trapped along the coastal areas. The marine layer can thicken and through a self-generating type of turbulence, force the marine layer to move inland. This action can result in a kind of wet fog along the coast. The relative humidity can be high enough to produce condensation on everything. This moisture laden air flows onshore nightly and permeates everything hydrophilic, including plaster, drywall and other building materials. As the warm morning sun comes out, the moisture is quickly driven off.

This change in humidity can have a dramatic effect on construction, particularly sensitive finish materials. The swing in relative humidity can be from a high 80 percent to a low of 35 percent in just hours.

This does not even account for our famous Santa Ana winds. These dry hot winds drive moisture out of everything in a hurry. The relative humidity during the Santa Ana’s is often below 10 percent. If you think all this has a minimal affect on buildings, you would be mistaken and the testing at Monash University in Melbourne, Australia, proves it.

In the 1990s, a group of researchers and construction experts from Australia and California were curious as to why certain regions experienced more cracking and crowning in drywall applications. Even when the best industry practices for installing drywall were followed, these paradise regions experienced problems with drywall cracking. The research included mock-ups that were exposed to swings in temperature and then swings in relative humidity. Surprisingly, the swings in the humidity had the far greater impacts than previously thought possible.

Paradise Lost

 I spent years outside of California construction. I can sympathize with my friends in Manitoba who are unable to work in the winter or in Seattle where working in the rain is just another day. I have been there with you. But California has its challenges, too. While most just see red tape and over-regulation, we know that the weather is also not quite so mild for the finish materials we put up. The problem just seems to get worse as designers and building owners are trending toward more smooth finishes and even higher levels of perfection.