Fire-Resistant Construction in California

It happened fast, taking 16,255 structures, causing 28 fatalities, and eating up 57,509 acres. The start of 2025 in California’s Los Angeles County began with a torrent of fire, emboldened by staggeringly high gusts from the Santa Ana winds, it consumed everything in its path. To the Pacific Palisades and Altadena residents and all the others who lost it all, you have our sympathy.

California building codes have a history of being stringent and in some cases are perceived as overly burdensome. Many of the strict building codes deal with earthquakes, of which there are many, that rattle the masses and challenge the integrity of the built environment.

Another stringent requirement are the environmental impact considerations that, because of the allure to live in the most temperate of climates, cause there to be a very high demand for new structures. And unlike the major metropolis cities of the east, here in the west we build out, not up, furthering the footprint of our residential and commercial structures. In the rebuilding of the devastated oasis that is California, I suspect there to be a very high interest and potentially codified increase in fire-rated construction. And that is where this month’s article is going to venture.

Claddings Tested and Approved

Let’s look at our stucco and EIFS claddings that have been tested and proven to perform against fire incidents, and some introductions of non-mainstream components and systems that meet fire and thermal thresholds. One of the mitigating factors in the L.A. County fires was the fact that high winds were carrying sparks and depositing them in fuel-laden areas and into cracks and crevasses sparking yet more fire.

The residential Achilles’ heel are the attic-vented roof structures, where the increase in atmospheric pressure from the high winds created a negative pressure differential in said attics to which the sparks flew into, to begin their total destruction. Once the flying embers landed in a home attic and started a fire, there was nothing to be done but flee and pray. Many of these homes had three-coat stucco exteriors and were standing firm against the onslaught until the embers breached and attacked from the inside. In short, no fire code in the world could have prevented this damage.

Fire rating requirements in claddings fall into “hour” ratings with the one-hour being the benchmark. Our storied cladding hero, three-coat stucco, offers a one-hour fire rating. The rated assembly providing that if the stucco wall was exposed to fire, it would be an hour before the fire could breach to the interior. Primarily the fire rating is to allow occupants time to get out of the structure. Three-coat stucco homes and commercial buildings many times are the lone surviving structures after devastating fires. A cement stucco wall coupled with cement roof tiles and perimeter CMU yard walls make for a formidable line of defense against fire. This combination has time and again stood against the crucible of destruction.

One Coat Systems

Some building exteriors are clad with one-coat stucco. This cladding also offers a one-hour fire rating. In residential construction throughout the Southwest, one-coat is applied over fire-treated EPS foam, over a WRB, over open stud framing. Most of the one-coat manufacturers have tested their products in this configuration to pass the fire test. In a fire, the EPS foam melts away leaving the cladding standing all by itself having done its job of staving off the flames while the occupants evacuate. Typically, in commercial one-coat clad stucco structures, there is an exterior sheathing onto which a WRB, lath and stucco are applied. EPS foam is only installed when extra thermal performance is desired.

And speaking of EPS foam, EIFS claddings have been tested and passed the rigorous NFPA 285 fire testing. In this configuration, the EPS is either adhered or mechanically attached to a substrate. The base coat and mesh (lamina) are applied over the foam and when combined, provide the resistance to the flames for the critical one-hour occupant exit window. The heat from the fire melts the EPS rather quickly turning it to a hot liquid.

The moisture in the sheathing attracts the hot liquid to its surface (the law of thermal dynamics) and the liquid EPS slides to the bottom of the wall where it is pooled. This is why we backwrap at the bottom, so EPS won’t be exposed to the flames. (Description courtesy of a major EIFS companies’ engineers). A relative newcomer, only as it pertains to being incorporated into EIF systems, is mineral wool.

Most IFS manufacturers have developed systems that use mineral wool instead of EPS. When it comes to fire protection, mineral wool is a beast. Made from molten rock, it takes a lot of fire to alter its composition. I have no application experience with this configuration so I cannot attest to its ease of application vs using EPS. Mineral wool is also being used in the application of insulated stucco claddings.

There are many options for stucco over foam configurations and mineral wool is easily substituted. Since stucco is an assembly and not a system, there are many configurations available limited only by one’s own imagination. I have seen a few “doozies” and have heard of these jokingly referred to as “Frankensystems.” I do not disparage these assemblies and have applied a lot of stucco over foam in my tenure as a plasterer. I do know of one single-source insulated stucco assembly manufacturer named Brand X Metals which has an engineered system called Diamond Furr. This utilizes trims designed for exterior insulation onto which metal lath is wire tied.

Clean-up efforts are underway in the ravaged areas and re-building will soon begin.

I expect there to be a different landscape, a built environment with newer technologies. Energy efficient structures with protective exterior envelopes and high-tech heating/cooling/venting systems. A sealed environment where no spark can enter, no eaves to harbor the aggressive embers, a truly airtight environment. The Santa Ana winds will rear up every year and fires may start, but hopefully we can outsmart the scorching.