Recent increases in interest rates have had an adverse effect on the housing market, and new-home construction has slowed significantly nationwide. This current valley follows nearly 10 years of peaks for the housing industry that resulted in a significant surge in land prices and new home costs.
Higher-density construction emerged as a means to reduce the sticker price for new houses. The developers built houses that were smaller and closer together, with the narrow street frontage (35 to 40 feet) facing much narrower streets (20 to 25 feet wide), some of which are dead ends. This way the developers could build more units per acre. In theory, this would decrease the cost of land per unit, thus lowering the cost per house and making homes more affordable to the consumers.
But as we all know, supply and demand is the name of the game in our market-driven economy. Needless to say, the altruistic facade of affordability faded away as fast as the rapid pace of the construction boom. And throughout the country the prices for new houses continued to soar at record rates.
These cluster subdivisions not only challenge the fire protection concepts of the construction codes for residential dwellings, but even push the envelope for the good old-fashioned common sense of general community safety. It is easy to figure out that on a bad fire day, lots of dry lumber piled up very close together could result in much bigger fires.
The International Code Council publishes the International Residential Code that governs construction of one- and two-family dwellings not exceeding three stories in height. Based on the provisions in the 2003 edition of the IRC, the exterior walls of the house were not required to have fire-resistive rating if they were not closer than three feet to the property line.
Fortunately, ICC eventually recognized the significant fire exposure problems, and its 2006 edition of the IRC, modified the 3-foot requirement to a minimum of five feet away from the property line. If the houses are designed closer to the property line, the exterior wall must be a one-hour fire-resistive rating.
Out here in the West, these non-rated exterior walls are mostly constructed of 2 x 4 framing, with a layer of 1/2-inch gypsum board on the inside, expanded foam in the middle for insulation, chicken wire, and then finally a layer of stucco on the outside of the wall. Generally, the major difference between the non-rated wall and the one-hour rated wall is that the 1/2-inch gypsum board is little thicker (5/8 inch).
Remember that the one-hour fire-resistive rating doesn’t necessarily mean that the wall will last for one hour during an actual fire. The fire-resistive rating was established decades ago during the laboratory testing. An even more important fact to remember is that when the exterior wall is between three and five feet from the property line, the IRC allows for 25% of the one-hour fire-resistive exterior wall to be unprotected openings such as windows or vents.
Having all these areas of unprotected openings should make us think twice about the fire-exposure problems. In these cookie-cutter tract home cluster designs, the windows and vents are in close proximity to or directly facing each other. The closer together they build these cluster dwellings, the higher the chances of fire jumping from one house to the next.
In a fire scenario, especially with wind conditions, the heat from the fire in one house could definitely create fire exposure hazards for the neighboring house. The heat could begin melting the expanded foam insulation inside the exterior wall of the second house, getting that one involved also. That is, of course, if the fire has not already jumped across those unprotected bedroom windows and vents to the neighboring dwelling.
In these situations, residential fire sprinkler systems could be a great solution. Clearly, by extinguishing the fire in the incipient stage, fire sprinklers save the occupants lives. But then for most fire scenarios — other than the attic fires, as codes do not require installation of fire sprinklers in the attics of one- and two-family dwellings except as needed to protect fuel-fired equipment — fire sprinklers could also significantly reduce the probability of conflagration. That would then decrease the fire exposure intensity for the neighboring structure, thus reducing the probability of fire jumping from one building to the other.
In one- and two-family dwellings, regardless of the fire-resistive rating of the exterior walls, residential fire sprinkler systems could provide a much higher degree of life safety for the occupants of an involved house than can the passive fire-resistive rating of their exterior walls. The fire rating of the exterior wall is merely important for the fire exposures from the outside.
With the fires on the outside, the inside of the house would still be tenable, at least to a degree to afford the occupants of the house the chance to safely evacuate. If the fire in your neighbor’s house is controlled by the residential fire sprinkler and contained, the fire rating of your exterior wall maybe of importance for the property protection purposes, but of less value for your life safety.
Also, by stopping the fire progression, fire sprinklers provide a much higher degree of safety for the firefighters. In confronting a fully involved structure, firefighters could face a higher probability of structural collapse, especially with the newer built houses that have lightweight wood trusses. And as you know, the fire service has long been concerned about the structural stability of these lightweight wood trusses under the adverse fire conditions.
As a result of these concerns, Department of Homeland Security recently awarded Underwriters Laboratories a grant to study the structural stability and performance of the engineered lumber and lightweight wood trusses under adverse fire conditions. The results of this study will be quite valuable and could even further highlight the importance of residential fire sprinklers in protecting our own firefighters. After all, by discharging water at the earliest stages and containing the fire, structural members would not be exposed to the flames; therefore, risk of structural failure is eliminated.
In part two, I’ll discuss the need to get aerials on the scene and some of the forces at work against this goal.
November 13th, 2007 @ 8:27 pm
Forgive me if I misunderstand your argument, but it sounds to me like you started with the premise that domestic sprinklers were the answer and sought to justify them as the solution to the exposure fire problem you describe rather than considering alternatives. Why wouldn’t further changes in exterior wall fire resistance ratings exterior opening allowances make more sense if we are trying to reduce the chance for building-to-building fire spread? After all, your argument acknowledges the risks of attic involvement, which seems a pretty likely scenario in high wind conditions. If sprinklers cannot attack the fire until it spreads to an adjacent dwelling, I submit we’re better off looking again at the separation and fire resistance requirements rather than piling on additional arguments for domestic sprinkler systems.
November 14th, 2007 @ 12:58 pm
This was a long article that was split into two parts for posting. The second part of the article might better explain my reasons, but here is one part of my logic. Regardless of the fire-resistive rating of the exterior wall, even if it was four-hour rating, the current code allows 25% area of unprotected openings. Thus, with the cookie-cutter designed buildings only six feet apart, fire will involve the second building through those unprotected openings. Then the best thing is to put out the fire with the residential fire sprinklers. And even if the fire was in the attic, there would be more probability of property loss than loss of lives. So from the life-safety perspective, in my opinion, it is best to have fire sprinklers.
December 3rd, 2007 @ 9:50 am
As I interpret the original article, two separate scenarios are presented. The first is that the density of construction is decreasing the abilities of firefighters to gain access to residential fires and increasing the likelyhood of exposure fires. Fire sprinklers would decrease the need for the response of multiple fire units to these subdivisions solving the access problems and the fire severity, where separation and fire resistivity may not.
The resonse by kiwichief seems to timply that fire sprinklers would increase the cost of construction and not solve the density issue. I think he fails to understand that increased fire resistivity adds to construction costs and separation reduces the number of builidng units, thereby costing the developer more than fire sprinklers would cost. Regardless of the type construction, separation, or the installation of fire sprinklers, a fast moving wild fire will spread from building to building, but with fire sprinklers the fire severity, and the damage to the individual building will be reduced.
The bottom line is that regardless of the type of construction and separation dwellings, civilian deaths will continue to occur and firefighter fatalities will remain status quo until the opponants of residential sprinklers see the light.