Generally there are five types of building construction agreed upon between the International Codes Council (ICC) and the National Fire Protection Association (NFPA) 220 – Standard on Types of Construction.
- Type I – Fire Resistive
- Type II – Noncombustible
- Type III – Ordinary,
- Type IV – Heavy Timber
- Type V – Wood Frame
Each has its own positives and negatives. All can be faced by those in the trenches at some time or another. Now coming into view, in regard to building construction, is green construction, using renewable materials within and on the structure.
Type I — Fire Resistive
With Fire Resistive construction, we see several factors that have the ability to assist firefighters. This style of construction does have some flaws that need to be noted. The definition we all learned at one time or another has been “Structural members including walls, partitions, columns, floor and roof constructed of noncombustible material.” What does that mean? It simply means that the major structural components, floors, walls and roofs will not lend themselves to the fire (as fuel). These buildings “consist of mainly reinforced concrete with structural members (walls, columns, beams, floors and roofs) being protected by blown-on insulation or automatic sprinklers.”
The walls and floors tend to compartmentalize the fire and hold it in one area. The primary fire hazard in this, as with all the others, is the contents — the stuff we put into the structure. As the insulation is knocked off/scraped off, exposure of the structural steel components to the heat leads to elongation and collapse.
Other troublesome issues for us are access — some forms of forcible entry and structural breaching are time-consuming and very tough. Large debris masses from structural collapse cause these buildings to hold lots of heat due to the materials used in the contents, as well as some construction features. One other note on these buildings: the fire-resistance ratings on floors, walls and structural supports are under laboratory conditions — not the real world. The hour ratings of these assemblies “measure how long assemblies maintain load-bearing ability under fire conditions — NOT how difficult it is to fight the fire.” It buys time for the occupants to leave and firefighters to mount an interior attack — if possible.
Type II – Noncombustible
Noncombustible construction has the same materials as Fire Resistive; the difference is Noncombustible construction has no form of fire-resistance protecting the structural steel components. These buildings have lower fire resistance ratings — remember these are done in labs. Now that the steel is unprotected, we can expect the structural steel to elongate — four inches for every 100 feet. If the steel can’t elongate, it will warp, twist and fall down, which equals structural collapse. If there are serious dead loads, live loads or any other loads the building is under, it will lead into a very bad day.
Contents are still a problem. These buildings are common construction and relatively cost-effective for the owner. Other problems are the metal decking flat or pitched roofs. Flat roofs are several layers of insulation, roofing paper, neoprene liners for weather resistance, tar and gravel and not easy ventilation tasks. The pitched roofs may have lightweight panels for lighting and that equals burn through, or ventilation along with firefighter step through. Remember to sound your roofs. These buildings also hold heat well.
Type III – Ordinary
Ordinary construction is traditionally considered “Main Street, USA” where buildings built on the main street of the town are constructed of masonry walls and timber within, usually three to five stories. Cast iron fronts, beams and some girders are found in these buildings. Wood components are smaller than heavy timber components, but larger than most wood frame components. Most of these buildings were used as retail spaces at the street level, with offices or apartments above. These buildings are aging — 100 years old, and in some places, older. Some serious modifications have happened in their lifetimes.
Key factors are the load-bearing walls; two are load-bearing and they hold the joists, two are non-load-bearing. Look for vent openings between the joists — cockloft/attic space indicator — that usually run with the street direction, but not always. Void spaces are rampant in these buildings with all the changes they’ve seen.
When fires enter these spaces, it quickly takes control of the building. These buildings can be vertically vented, although it may take a little time with the layers of roofing material or the rain roof (roof over an existing roof) added later in life.
Type IV – Heavy Timber
Heavy Timber construction is also known as mill construction. These buildings were originally built for heavy machinery and processing of materials. Originally built with thick masonry walls, big pieces of wood (larger than eight x eight inches) as the structural components and several layers of wood flooring, they offer some values. Without full automatic sprinkler coverage, be prepared to do battle quickly and hope for a quick knockdown. If not, defensive operations with lots and lots of water for an extended period of time can be expected.
These buildings may also have the floor joists fire-cut. A fire-cut is where the ends of the beams are cut at an angle inside the masonry wall to allow the floor(s) to fall into the building to maintain wall stability. We may also find bowstring trusses in the roof or arched roofs. Heavy timber construction happens today in some church sanctuaries using laminated lumber to get the heavy timber look, or assembly occupancies looking for a natural feel to their structures. As these buildings age as well, the modifications made include unprotected steel assisting the structural components already there. Some components may be removed as well, and that leads to structural collapse.
This building is a true double-edged sword — it will take some time to get going and stay structurally sound for a long period of time, but when the fire takes over — heat generated by those timbers creates problems for any exposures in the area.
Type V – Wood Frame
Wood Frame construction is the most familiar to all of us. A large part of our living, training and learning occurs in these structures. It’s where we’ve “cut our teeth” and learned our trade, for the most part. Besides, residential structures outnumber everything else. The evolution here came from log cabins, to balloon-frame, then platform, and now lightweight construction. Small dimension lumber used for most frame houses. We now find wooden I-beams used in floor assemblies; although they are a strong weight-bearing material, they fail miserably under fire conditions.
Documented cases show where houses are collapsing as the first-due apparatus arrives on scene. Now found are aluminum studs, laminated timbers, aluminum joist hangers, gusset plates and all kinds of truss assemblies. Be aware that air handling units are in attic spaces, adding to the dead load the trusses have to support — especially with fire burning underneath. Outer skins range from wooden grooved plywood siding, wooden siding with boards, Masonite® siding, aluminum or vinyl siding and finally brick.
One of the most common size-up mistakes I hear is a “residential structure with masonry construction.” Masonry is a component — not a style of construction. The brick you see is a veneer — a single layer of brick for looks only. Although there are some Type III - Ordinary construction single family buildings, knowing your buildings is vital to you and your crew’s lives.
Now added to all this basic information are more changes: green construction with reusable materials, hybrid construction methods where several of the different types of construction are melded within a single building and construction methods that get lighter and cheaper. Add to that buildings under construction, renovation and demolition — those are hazards on their own. With all this, how is it possible to keep up? Diligence and study — on duty and off — allows us to perform at our best. Knowledge is one of the best tools to have.
This is only the tip of the proverbial iceberg. We all have to keep up with changes, and building construction is no different. Take time to really look at the buildings you protect, already standing and under construction. The more we learn about the battleground we fight on, the better we will survive and pass on that information to the next generation of firefighters.