scourge of termites. For the new year, we continue our series by getting more familiar with two more important aspects of LGMF:
• Fire resistance
• Mold resistance
Fire resistanceAs stated in part five, termites cause more damage annually to homes in the U.S. than fire does. That's not to say that fire doesn't take a significant toll on life and property-on the contrary. According to the National Fire Protection Association, in 2002 the equivalent of one house fire occurred every 79 seconds causing 2,670 deaths and 14,050 injuries. In economic terms, more than $6 billion in property loss resulted from these 401,000 house fires. Part of the problem is the nature of the wood framing typically used to construct houses-it is combustible, thus it provides fuel to feed a fire and contributes significantly to the spread of the fire throughout the structure. In fact, the wood framing of a house is third on the list of "first ignited" materials in a house. Essentially, the wood framing acts as kindling and a pathway for the fire to spread.
In a traditional stick-built wood frame structure, fire spreads quickly from the ignition point. In a LGMF structure, the fire is contained better. Since LGMF is incombustible (will not support combustion), the fire is denied the opportunity to spread rapidly from its source allowing the occupants precious time to make their escape. In a fire, seconds can make the difference between life and death.
In July 1996, a fire started in the kitchen of a single family LGMF home in Brentwood, Calif., while the owners were away. This fire became a case study for the effects of fire on a LGMF structure. Though the fire caused $75,000 worth of damage, there was only superficial damage to the structure. A metallurgical analysis examined both unaffected and charred studs. The result was confirmation that both-unaffected and charred framing components- from the Brentwood home maintained the integrity of all their structural properties:
• Yield strength (33KSI: typical for LGMF)
• Tensile strength
• Total elongation
On the charred framing components, the zinc coating (galvanizing) remained intact or "alloyed" (from the heat of the fire) with the base metal (steel) substrate to form a lightly iron-rich coating dubbed "galvannealed."
Since the early '80s, the American Iron & Steel Institute has been testing and developing fire ratings for load bearing wall assemblies pursuant to the ASTM E119 standard fire test. As a result, UL Design U425 includes fire resistance ratings, construction and material details for such assemblies. Building codes typically require LGMF assemblies to use UL or ASTM tests to achieve fire resistive ratings. Since LGMF has been used widely for many years in non-load bearing commercial interiors and curtain-wall applications, such ratings typically include the fire rating (in hours) whereby an assembly can contain the fire, smoke and heat while maintaining its integrity.
Though the database is not yet sufficient to develop insurance risk calculations, as it exists for wood frame houses, in 2003 the developer of a large, multi-family residential project in California saved $400,000 in his builders risk insurance burden for utilizing LGMF in lieu of dimensional lumber. Such opportunities for significant insurance discounts for builders/developers is not exclusive to the Golden State-it is nationwide. Word-of-mouth and anecdotal evidence, such as the Brentwood fire, tip the scales in favor of LGMF where fire resistance is the subject of debate.
Mold resistanceWhenever mold is discovered, moisture is always the main suspect. In a moisture-rich environment, mold spores feed on nutrients found in susceptible materials and grow exponentially. Whenever moisture penetrates a building envelope precipitating mold growth, there are serious consequences: lost income, health care and remediation costs, higher insurance rates and endless litigation. Mold and mycotoxins can trigger allergic reactions in sensitive individuals and even cause lung cancer. Since mold has adverse affects on indoor air quality, the more mold resistant the structure, the healthier the indoor environment will be as the net result.
On a typical construction site, there are to be found thousands of known strains of fungus (mold) producing microscopic spores on such common surfaces as wood, paper, carpet and food. Mold exists naturally, both indoors and out, where there is an environment for it to feed on. Most conducive to mold growth are areas with excessive moisture, a sufficient food source and suitable ambient air (temperature) conditions-like the cavity of a framed wall or an air duct. Mold is a survivor and will digest whatever it grows on in order to survive and multiply. The game is about controlling its spread, not eliminating it entirely-that would be impossible. Some mold susceptible materials include many of the most common building materials:
• Gypsum board
• Oriented strand board
• Wallpaper glue
Paradoxically, the advancement of building technology over the past 30 years has made the indoor environment of commercial buildings more susceptible to mold than ever before. Tighter building envelopes with better thermal insulation and efficient HVAC systems meant less exchange between stale indoor air and fresh outdoor air. Though these new technologies reduced energy costs significantly, higher relative humidity levels and indoor pollutants re-circulating rather than exiting is the main cause of sick building syndrome. To decrease high relative humidity levels, modern HVAC systems employ "desiccant" elements to absorb moisture from outside air before it enters the indoor environment. Think of the little pouch that comes with Japanese rice crackers to keep them fresh and crispy-same idea, that pouch is a desiccant material to absorb moisture.
Infiltration of water: Typically around window and door openings, roofs, foundations, plumbing, etc., is another factor in the growth of mold. Thus, the tighter the building envelope (provided with proper ventilation) the less likely mold will gain a foothold. Too often, tight buildings lack good ventilation. Like love and marriage-you can't have one without the other. Uniform and dimensionally stable, LGMF consistently produces straight floors, walls and roofs resulting in better, tighter fits for doors and windows and an overall tighter building envelope than is possible with wood framing. Being inorganic, LGMF does not provide a food source for mold as does wood. A lighter and more resilient structure resists sagging and the movement that can/does cause cracks and crevices in the building envelope. Keeping moisture/water out is the first line of defense in mold resistance, denying it a food source is second. On both these scores, LGMF is the best defense.
In part seven, we'll conclude our familiarization series on LGMF with a look at its "green" aspects, price stability, adaptability and some recommendations based on what we've learned.