EIFS and Earthquakes
At 11 a.m. on Wednesday, Feb. 28, my laptop became an in-my-lap laptop. A 6.8 earthquake hammered Seattle, my laptop (and lots of other things that weren’t tied down) sailed around the room briefly, and the phone hasn’t stop ringing since. E-mail requests from my Web site (www.eifs.com) are piling up, too. People want to know how EIFS behaves in earthquakes and if their building is OK.
Those of you who live in areas not known for earthquakes are probably thinking, “I’ll pass on this month’s EIFS column.” Think again. There are many areas in North America that are seismically active, including the Rocky Mountains, the Tennessee Valley area, the central Midwest, and sections of the East Coast from Georgia to Maine. Clearly, earthquakes are not just a West Coast issue. This month’s column will give you some insights into a specialized area of EIFS knowledge, namely, how EIFS fares in earthquakes.
The short answer to how EIFS fares in earthquakes is simple: very well indeed. There are many reasons for this, but two characteristics of EIFS are the key: weight and flexibility.
The lightest oneEIFS is one of the lightest claddings; name one that is lighter. This is desirable from an earthquake standpoint because heavy materials, once they start moving around, are harder to get to stop moving than lightweight ones. Think of it this way: If you are in the penthouse of a high-rise building and a quake occurs, the top of the building will sway. Objects tend to want to stay where they are, but when prodded by external forces, they will move. For example, a piano of casters may go sliding across the floor and cause trouble, but a bag of EIFS insulation boards sitting on the floor is unlikely to do much damage. The same concept applies to claddings. Light is good.
The light weight of EIFS is also no small factor in areas where earthquakes are an everyday affair, such as in New Zealand and many parts of Asia. I’ve worked on EIFS projects around the Pacific Rim that involved adding extra stories to the tops of tall buildings. In several instances, EIFS was selected specifically because it doesn’t add much weight. This was not only because of the demands that the extra weight would place on the buildings’ existing frame and foundations, but also because it doesn’t make the building top heavy—a plus in earthquakes.
The light weight of EIFS has another benefit if The Big One occurs. If a building itself is taxed to its structural limits and starts to come apart, EIFS, being a monolithic material, tends to stay in one piece.
Compare this to what happens (all too frequently) in earthquakes made of lots of small, hard, heavy pieces: Masonry façades come loose, pelting the street with heavy debris that can knock you down—or worse. Firefighters will tell you a similar story: that of someone crushed by a huge masonry wall that collapsed unexpectedly; it is one of the scariest aspects of fightingfires on old buildings.
EIFS wobble but don't fall downThe flexible nature of EIFS is another big plus for EIFS in earthquakes. EIFS tends to “give” and deform when subjected to extreme forces. Unlike other more rigid materials (brick, for instance), EIFS does not tend to crack and suddenly come apart. This ability to “give,” a type of behavior known as ductility, is desirable in earthquakes. Ductility, or the ability to absorb force and yield without suddenly failing, is desirable. The opposite of ductility is brittleness. Glass is brittle (it fails all at once), while wood, for instance, bends appreciably until its limits are reached.
EIFS is often attached to lightweight wall structures, such as studs and sheathing, which also “give” a lot. This light framing is often also attached to a limber steel building frame. In all, many EIFS-clad structures are tolerant of the shaking and racking that occurs in earthquakes. This makes for a safe situation, despite the fact that the building may be swaying like mad. It sure beats having the building collapse.
Interestingly, the recent Seattle earthquake pointed out an interesting fact about EIFS’ sister product, Portland cement plaster, or stucco. Seattle has lots of stucco and EIFS, and I saw a number of older masonry buildings next door to EIFS and stucco buildings that fared poorly. Most of the problems were cracks or toppling of sections of the façade. Contrary to commonly held beliefs, stucco is actually a membrane that “floats” on the outside of the wall. Stucco is not bonded to the wall (barrier EIFS are) because the building paper, in addition to providing water penetration resistance, also de-couples the stucco from the sheathing. In fact, stucco simply hangs on the lath fasteners like a curtain. This allows stucco, which is a brittle material reinforced with metal, to “give” a bit when a wall racks during an earthquake.
In all, EIFS performed well in the recent earthquake. The damage to the metro area has been estimated in excess of $2 billion. But because EIFS looks like concrete, many building owners do not understand its true nature, and the requests to check EIFS façades keep coming in. In a sense, the recent shake has been good for at least one kind of business in Puget Sound: the wall and ceiling industry. It’ll take months to fix all the cracks.