From Fire Engineering.com February 1, 2011
BY DOUGLAS J. MITCHELL JR. AND DANIEL D. SHAW
The recent dip in our economy has slowed down many new construction projects, but “Johnny Appleseed” continues to build residential homes. Who is the “Johnny Appleseed” Construction Company? Well, it operates in almost every town, city, and state. Much akin to “Johnny Appleseed,” these builders seem to magically spread house “seeds” in any tract of open land or in your local farmer’s backfield (photo 1).
|(1-2) Photos courtesy of Google Earth.|
After a few months, up sprouts a community of 30-plus similar looking homes—additions to your fire department’s first-due response area (photo 2). The construction company’s name is insignificant, be it “Johnny Appleseed” or not. Most builders follow similar techniques for home construction when producing these multihome developments.
Statistically, we know that most fires in the United States occur in residential buildings. As such, we must keep up with current trends in residential building construction. You can do this by understanding building construction and conducting site visits during the building phase.
There are four commonly accepted subclasses of wood-frame construction:
- Post and Frame. This building design was prevalent in the early settlement days of our country and now is making a resurgence, in part because of its durability. It uses larger dimensional posts to form the outer skin of the building; its connection points typically are mortised or connected with pegs. The remainder of the walls can be composed of a mortar mixture or, in a hybrid design, have foam panels or engineered wood. The advent of prefabricated structural insulated panels (SIPs) has made this design more energy efficient and decreases construction time.
- Balloon Frame. This style incorporates the framing of the outside load on bearing walls with limited fire stops from the lowest point in the home to the roof/attic area. The use of dimensional lumber may afford some level of fire and collapse resistance, but the prolific number of voids will cause fire to travel unimpeded from floor to floor.
- Platform Frame. This common design in the residential arena incorporates the complete building of a story (floor joists, subflooring, walls) on top of another story until the completion of the home. Typically, this would terminate at the second- or third-story level. Platform frame provides fire stopping between each floor level, and vertical voids are limited. The use of dimensional lumber, coupled with strong connection points, offers greater resistance to collapse than the Lightweight subclass.
- Lightweight. The most common and cheapest method of construction is also the most dangerous for firefighters to operate in because of its reaction when exposed to fire. Although employing the platform-frame style, lightweight construction uses smaller-dimension lumber (2 × 4s) that may be composed of engineered wood, which, in some cases, is merely wood chips and glue compressed to carry a load. The connection points between these members can be weak and can fail early.
Both old and new construction types pose well-documented hazards for firefighters and have specific fire travel concerns. In older homes, where dimensional lumber may afford us longer resistance to fire, its construction design often allows fire to travel unobstructed through vertical voids, such as those found in “balloon frame” home exterior walls.
Most commonly seen today, lightweight construction relies heavily on the parallel cord or open web floor truss and lightweight peaked truss roof. Compartmentation between floors (partly because of the platform frame) in newer houses has decreased vertical fire spread in voids. However, horizontal fire spread has the potential to increase throughout the structure. Fire can travel in rough-cut openings in floors and ceilings and through knock-out tabs in wooden plywood I-joists, added so various utilities can pass (photos 3-5; note in photo 5 that the entire web burned out). Fire in open-web flooring truss systems can pass unabated throughout an entire floor area.
|(3) Photo by Captain Dan Shaw.|
|(4-5) Photos by Lieutenant Douglas Mitchell.|
This form of construction has also decreased the thickness of structural members exposed during a fire. The structural support components in the plywood I-beam and open web truss-constructed joists weight-carrying top and bottom chords are now commonly seen finger-jointed and glued together. They are no longer one continuous piece of wood. In an older home where the thickness of dimensional lumber might have held a fire to one or two ceiling bays, a fire today may now travel across the floor support system from end to end, exposing all sides of the truss support system and quickly burn through the web of the plywood I-beam.
Connection points to vertical supports are also less substantial and are comprised of lightweight materials such as gusset plates and metal hanging brackets. Although these lightweight materials (joists and attachment points) are often rated to carry heavier loads and span longer distances than conventional dimensional lumber, their breakdown rate under fire is significantly quicker. We must prepare ourselves for the potential of early failure in these components when they are attacked by prolonged or intense fire conditions.
VISITING THE CONSTRUCTION SITE
The best time to make your visit is as the “Johnny Appleseed” Construction Company breaks ground and is “sprinkling” the new home seeds on what was the farmer’s field.
“Johnny’s” residential construction plan usually has three or four houses under construction at a time, all with varying levels of completion. With this method, the company is able to keep many contractors working at the same time. Most homes are completed in an assembly-line fashion, where workers move from home to home, street to street, until completion.
This construction method can be an enormous asset for us as future responders to fires and emergencies in these structures. Firefighters now can see various construction components in position during differing stages of home completion all in one visit to the development site.
Take the fire company over to the site and talk with the construction/on-site manager (photo 6). We prefer the company-level visit; however, some larger building developments may require that a higher-ranking officer set up an appointment with a representative of the construction company because of safety and security concerns. Either way, most site managers we have encountered are more than willing to allow a site visit.
|(6) Photos by Captain Dan Shaw.|
Before you even get out of the rig, what can you see? Are there flag lots and pipe-stem courts? Are there sufficient hydrants? Are there “stick built” components (2 × 8, 2 × 10), or are there preassembled components (i.e., truss floors, roofs, I-joists). Look at the materials on the job site for clues as to what may be inside the houses.
Conduct a 360° examination of the exterior (photo 7). Note the presence and locations of windows and doors. Do the houses have basements? Basement fires are often some of the toughest and most dangerous fires we fight. Are there variations in basement access points (i.e. walkout door), or are there only small windows with a window well in each home (photo 8)?
|(7-8) Photos by Captain Dan Shaw.|
Many newly constructed residential homes are going “green.” These new ideas will pose new hazards for us. Note any components you haven’t seen before in your town such as solar installations or new insulation materials (such as SIPs). Energy efficiency and “green” components, such as solar panels, are making a resurgence in the housing market, especially since the government often provides financial incentives for the homeowner incorporating them in the construction. In reference to the prefabricated SIPs, they are essentially two pieces of oriented strand board with foam or polyurethane mixture innards glued between (for more on SIPs, visit www.sips.org). This foam center core offers greater insulation qualities for the home but also can quickly add to the fuel load and increase the rate at which fire will travel in this void. The fire’s removal of the foam support will compromise structural integrity.
Once inside, look at the house beginning in the basement. What is the foundation for these homes—block or prefab insulated form? What is holding up the first floor? Laminated “I” joists or steel beam over lally-columns (photo 9)? Identify the structural components throughout the home and the structural hierarchy of the structure from the most important to the least important members.
|(9) Photos by Captain Dan Shaw.|
Note any similarities in the layouts of each of these structures. Often, there may be only two or three model floor plans for the entire development. Builders may vary the front facades to give the illusion of a completely different home, but the interior components and layout remain unchanged. They also commonly “flip flop” or “mirror image” the floor plans in homes next door to each other. Most importantly, mentally “burn the building down,” and visualize the fire attacking the structural components of the home, floor by floor. What are the weaknesses and vulnerabilities of these components, and how will they impact your operations? Where can you anticipate the fire to travel next?
Take the information your company gathered back to the firehouse. Plan to incorporate your findings in your next company drill. Tactical discussions based on your discoveries will make for a great drill. Develop fire attack plans, and have suppression strategies in place before you respond to a fire in this new development. It is certainly wise to have these plans established long before you are advancing lines and crawling in with zero visibility and people trapped.
Use the “Johnny Appleseed” multihome construction techniques to your advantage. Get your company out to visit these developments, and do it frequently. Proper preplanning is just one facet in getting you, your company, and your department members “combat ready.”
Originally posted on Fireengineering.com 02/01/2011 All Rights Reserved http://www.fireengineering.com/index/articles/display/6402826502/articles/fire-engineering/volume-164/issue-2/features/preplanning-new-construction.html
DOUGLAS J. MITCHELL JR. is a lieutenant in the Fire Department of New York with 17 years of experience. He previously served with Fairfax County (VA) Fire & Rescue. He has been published in Fire Engineering, has presented at FDIC, and lectures on fireground topics as a vice president of Traditions Training, LLC.
Daniel D. Shaw, an 18-year veteran of the fire service, is a captain with Fairfax County (VA) Fire & Rescue. He has an associate degree in fire service supervision and a bachelor’s degree in business administration. He has instructed at FDIC and has been published in Fire Engineering. He is a vice president of Traditions Training, LLC.