In part four, we discussed the various aspects of light gauge metal framing. We began with a review of LGMF's most controversial aspect: thermal performance. The acute problem of thermal bridging associated with

LGMF and remedies for it were discussed at length. This month, we'll continue our discussion with a look at two more critical performance aspects of LGMF:

• Insect/pest resistance

• Earthquake (seismic) resistance

It might be of surprise to learn that annually, termites cause more damage to homes in the United States than fires do. For more than 50 years, Hawaii has suffered the scourge of the Formosan Subterranean Termite. Native to Mainland China, Taiwan (formerly Formosa) and Japan, it was introduced into the continental U.S. after WWII by ships and their cargo. In recent years, the Gulf States (Texas, Louisiana, Florida and Alabama) and even Georgia and the Carolinas have experienced severe damage to homes and trees.

The FST forms the largest colonies of any termite species in North America. A queen can live up to 30 years with her colony in extensive underground passageways that are 10 feet deep and half an acre in size. A mature colony consists of up to 10 million termites. The queen's long life span and prolific reproduction rate of 2,000 eggs per day provides exponential multiplication. The colony consists of a caste system of reproducers, soldiers, workers and the immature. Unfortunately, the only part of FST society that destroys wood happens to also make up the vast majority of the colony: workers. The reproducers of the colony are known as "alates." These winged termites swarm to mate in the spring and summer, shed their wings and form new colonies, thus spreading the problem far and wide.

An ounce of prevention

Considering the fact that most insurance companies do not cover the costs for remediation due to termite damage, avoiding the problem from the get-go makes a lot of sense. The Big Easy is a good place to gauge the extent of the problem. Between 1989 and 1998, collection traps revealed an increase of 2,000 percent in the number of alates FST's. Causing an estimated $300 million annually in property damage, New Orleans mandated the use of preservative treated wood in all new construction. The FST is known to enter treated wood through cut ends and tunnel through, devouring all wood in its path. As well, they will test the limits of chemical barriers and forage tenaciously. In Hawaii, $100 million is spent annually to prevent/control/repair damage caused by the FST.

As mentioned in part three, effective December 2003, waterborne chromated copper arsenate, the standard preservative treatment for building lumber for decades, was banned. The new copper based preservative treatments, ACQ, CBA-A/B and ACZA, are problematic in that they have a corrosive effect when in direct contact with steel. Sodium Borate preservative treated lumber is less corrosive to steel than CCA ever was in its long use as a pressure treatment for lumber. However, it is limited in its use since it cannot be left exposed to the elements.

Please, hold the sauce

LGMF with its galvanized (zinc) coating is off the menu as far as termites and other pests are concerned since it is inorganic and indigestible to termites. Quite the opposite is true for wood, even pressure treated wood, as we have seen. In fact, wood is at the top of the FST menu. Termite damage can/does undermine the strength/integrity of a structure. As we shall soon see, a structure needs all its structural integrity intact to resist the forces of inertia during a seismic event. With regard to termites, LGMF has great appeal as a building material, particularly where the problem is most pervasive: the Gulf and Southeastern states.

Once, on a visit to San Francisco in the late '80s, I experienced an earthquake firsthand. Mind you, I didn't know it was an earthquake immediately-it was more like a freight train going by real fast and real close. Instinctively, I knew something was amiss. My suspicion that I had indeed just experienced an earthquake below my feet was confirmed when residents of the surrounding buildings started to appear at their doorways and windows inquiring of one another about the strength and duration of the quake. Fortunately, it was a minor rather than a major earthquake (the latter occurring not long after my visit). Regardless, the power of that "minor" earthquake remains burned in my memory to this day.

Earthquakes can change the course of rivers, cause tidal waves and start devastating fires. Expanding from the epicenter, man-made structures are destroyed with ensuing loss of life. Seismic forces generate both side-to-side and up-and-down movement in the ground that is both erratic and powerful. Damage caused to structures is the result of inertia. Simply understood, inertia is the resistance of the upper portions of a structure to begin moving with the ground shifting as the result of seismic forces. If we recall our high school physics: "A body at rest tends to stay at rest unless acted upon by an outside force and a body in motion tends to stay in motion." Thus, once the resistance to moving by the upper portions of a structure is overcome by this outside force and starts to move, it wants to keep moving-not stop, not good.

Racking is the effect caused by the inertia of the earth shifting from side-to-side, thus causing the structure to move in the opposite direction of the sideways movement of the ground. The up and down movement of the ground or vertical inertia causes two effects:

• Compression: as the ground rises

• Telescoping: as the ground stops moving

Frank Lloyd Wright proved the forces of an earthquake could be resisted successfully with his design for the Imperial Hotel, in Tokyo (1919). After the city was devastated by a major earthquake and ensuing fire in 1923, the Imperial Hotel remained intact thanks to Wright's incorporating a "floating foundation" into the design of the structure. This allowed the foundation to move with the seismic forces in the ground limiting the effects of inertia on the upper portions of the structure. Ironically, the hotel and its fountain became a refuge and water source for the city's beleaguered population in the wake of the quake. Today, resistance to the forces of inertia are better understood and are incorporated into the design of structures to allow the building to "flex" with ground movement (to a certain degree) and absorb the energy of the forces in the ground, just like the architect's Imperial Hotel did all those years ago.

Whether a house is made of wood or LGMF, the same concepts apply to the science of seismic engineering, in factors, such as:

• Applicable building codes

• Engineering

• Design of structure

• Materials used for framing

• Quality of construction

All play a significant part in the seismic performance of a structure. Control of lateral forces is the key to the equation, since it is the sliding or racking motion that causes most damage. Primarily, lateral forces occur at the floor and roof levels tending to uplift or overturn walls. Therefore, it is critical to effectively tie the walls together and fasten them securely to the foundation. As well, all roofs and floors must be tied to the walls and the walls made "stiff" with bracing to resist lateral movement (racking). In this way, the floors and roof between these stiff walls will effectively limit the racking of the walls and transfer the seismic loads down to the foundation.

As the result of recent earthquake activity in California, building codes for LGMF have become more stringent and the testing protocols more rigorous. Of course, tangential to earthquakes are the firestorms that multiply the misery and destruction of earthquakes, even "minor' ones. Since LGMF is incombustible, it does not add "fuel to the fire" as does conventional framing lumber, which acts as kindling. Also, a wood framed structure subjected to termite infestation is weaker due to the fact that the termites literally "eat the structure." Slowly but surely, this degrades the integrity of the wood framing. LGMF suffers not from this malady-it maintains its structural integrity for its entire lifecycle. Though steel loses strength when subjected to the heat of a fire, as we shall see in part six, LGMF performs surprisingly well under fire conditions.

The big one

Most impressive is the fact that due to its higher strength-to-weight ratio, a LGMF structure is typically one-third the weight of the same wood framed structure. This translates into less weight, which means less inertia (less weight to stop moving). Also, LGMF uses a mechanical means of attachment, typically screws, whereas wood uses nails. Wood is subject to drying and shrinking causing warping and twisting of the framing. Since nails rely on friction and bending for holding power, as the lumber dries and shrinks, the friction between nail and wood declines over time thus weakening the structure. Dimensionally stability, a hallmark of LGMF, results in consistently straight floors, walls and roofs. Result: LGMF provides a tighter, more uniform structure.

With the facts now known, I don't know about you but I'd much prefer to ride out the next "big one" in a LGMF house. Next time, in part six, we'll continue our discussion with a look at both the fire and mold resistance characteristics of LGMF.