Firefighter Roof Support Systems

Study Notes

Firefighters must identify various roof support types and construction materials.
Different roof support systems behave uniquely under fire and collapse conditions.

Flat roofs can be supported by open-web steel joists or steel beams.
The simplest flat roof support utilizes wood joists, resting on load-bearing walls.
Wood joists function as beams, supporting roofing materials similar to floor systems.
Solid or laminated beams and columns may also support wood roof joists.
Traditional wood-joisted roofs utilize solid wood joists, which lose strength gradually when exposed to fire.
- Gradual loss of strength causes roofs to become "spongy" prior to failure.
Signs of softening or sagging in the roof are key indicators of potential structural failure.
- Misinterpretation of these signs may lead to overlooking imminent collapse.
Thin plywood or oriented strand board sheathing can fail rapidly without warning.
Advanced or heavy fire conditions indicate roof weakening; firefighters should be alert.
Roof support systems can collapse unexpectedly under fire conditions.
Box beams and I-beams, often made from plywood, may be used for flat roofs.
Wood truss joints typically support flat roofs but have vulnerabilities due to their thin web sections.

Slender components of truss joists are prone to quick failure during fire incidents.
Open web design allows fire to spread rapidly perpendicular to the truss joist, rather than only along its length.

Unprotected lightweight open-web joists can fail quickly under fire, depending on the fuel load.
Any unprotected material, including lightweight open-web structures, is at risk of failure during a fire.

In Type I construction, building codes may permit the omission of structural fireproofing for roof supports under specific conditions.
Unprotected steel roof supports may be present in buildings with fire-resistive main structural supports.

Roofs are engineered for lighter live loads compared to floors.
Modern flat roofs often experience deflection or vibration due to weight.
Flat roofs are primarily designed to bear the weight of maintenance personnel.
Under the load of firefighters, roof deflection may not indicate imminent failure but warrants cautious assessment.