Where have seismic requirements come from and where are they heading?

Historically, seismic construction was mostly on the West Coast with a little activity in Charleston and St. Louis. The old standards were entirely geographically based. You looked at a map and depending on the area would follow one standard or another or do nothing at all. It used to be simple.

Now, seismic requirements are based on three things: (1) Location. It's based on a map showing lines of equal earthquake forces. (2) Soil type at the building location. (3) Building usage. The requirements are more severe for hospitals than they are for something like a fast food restaurant.

With the introduction of soil and building-type standards, seismic design requirements for ceilings have spread all over the U.S.

Who is writing the code these days?

There used to be three model codes: the Uniform Building Code, written by ICBO, the National Building Code, written by BOCA, and the Southern Building Code written by SBCCI. ICBO, BOCA and SBC merged in 2000 and became the International Code Council, which writes the International Building Code. So, there is only one code now for the entire United States. That's the good news.

And the bad news?

The bad news is the code deleted all seismic ceiling requirements and instead references ASCE 7-02. ASCE is the American Society of Civil Engineers, and the formal name of ASCE 7-02 is Minimum Design Loads for Buildings and Other Structures. It includes wind loads, snow loads and earthquake loads. ASCE 7-02 (soon to be ASCE 7-05) further references two CISCA documents, which have the bulk of the details. So in the end, the IBC doesn't say anything except to look at ASCE 7-02. And while ASCE 7-02 gives some seismic requirements, it says to consult CISCA for the rest of the requirements. This change was prompted by the International Code Council's preference that whenever possible, technical requirements be referenced rather than actually included in building code itself. Thus, you need three documents to know the standards.

Do any localities do things on their own?

St. Louis, MO, Portland, OR, and, to a certain extent, Charleston, SC. Both Carolinas have slightly different interpretations and slightly different practices than do other states. New York City has its own code and the city's construction practice specifies what we call indirect-hung ceilings. Both CISCA standards require direct-hung ceilings. So, there is a big caveat for New York City. New Jersey also has slightly more arcane practices.

Which code is legally binding?

The IBC is only a model code. In point of fact, it has no effectiveness and no weight of law. True, the IBC is generally adopted by each state, but each state can change it, and they quite often do. State codes are then adopted by local jurisdictions, sometimes cities, sometimes counties, and they also can change the code and quite often do. A few states don't have state organizations. In those states all adoption is done by local jurisdictions. So, it's only down at the local jurisdiction that you find enforcement power.

Does the code specify requirements for ceiling panels?

No. All of the requirements are drawn up around the suspension system and the grid. The code says nothing about the panels.

Will the code change anytime soon?

Right now, the 2006 IBC will be published in February of 2006 and is expected to be adopted by local jurisdictions, including those in California, in 2007. The 2006 IBC references ASCE 7-05 for seismic requirements including those for ceilings. ASCE 7-05 is out, and the next planned revision will be ASCE 7-10. So the pace of revision is slowing, which should be pleasing to many engineers and building officials. In the long term, ATC-58 is developing some ceiling test protocols. Several organizations are jockeying for National Science Foundation (NSF) money to run tests, and it's indeterminate right now who, if anyone, will receive National Science Foundation (NSF) money. But at some point, somebody will run tests, and the results will drive the next round of code revisions.

You mentioned ATC-58. What is that?

ATC stands for Applied Technology Council. The Federal Emergency Management Agency (FEMA) is paying them to develop test protocols. ATC is a non-profit organization that performs studies for the government. It was founded by the Structural Engineers of California (SEOC), but at this point it's an independent organization. ATC-58 is developing test protocols for non-structural components, which includes suspended ceilings.

In summary then, what should architects do to get good direction on seismic ceiling compliance?

First, go to CISCA and purchase the two CISCA-recommended construction practices, Guidelines for Seismic Restraint for Direct-hung Suspended Ceiling Assemblies (zones 0-2) (2004 ed.) and Guidelines for Seismic Restraint for Direct-hung Suspended Ceiling Assemblies (zones 3-4) (2004 ed.). Each document is available at http://cisca.org/publications/reference.

Second, buy the ASCE 7. I would go with the '05 edition. The IBC references the '02, but there will be an IBC '06 coming out, and it will specify ASCE 7-05. Of course, there is no substitute for knowing your local building department. They are free to modify the code as they see fit. And a lot of them—especially in the larger cities—write their own procedures for their inspectors.

Anything else worth mentioning?

Remember, too, that the new seismic ceiling requirements are best termed "prescriptive." They are based on tests done in the mid- to late-1980s by CISCA in cooperation with the National Science Foundation. So, the origin of some of this stuff is test-driven rather than engineering analysis. As you might guess, since the mid- to late-1980s, testing equipment and facilities have advanced a lot. So you can expect to see a general increase in testing over the next few years.