Wood I-Joists Guide [PDF]
I-Joists & Firefighter Safety Guide [PDF]
Manufacture of I-joists
All web and flange materials are carefully graded to ensure they will perform properly in I-joists. The flanges range from 1-5/16" to 1-1/2" thick and from 1-1/2" to 3-1/2" wide.
Today, the web material used almost exclusively is OSB. I-joists manufactured prior to the early 1990s also had webs made of plywood. Web material in typical residential I-joists is either 3/8" or 7/16" thick.
Performance Requirements for Code Acceptance
Although I-joists differ among manufacturers, they are all manufactured to an industry consensus standard. I-joist performance is closely monitored by the manufacturer and an independent third-party quality control agency. The quality control program assures the product continually meets code-recognized test standards. The two most important performance characteristics are strength and serviceability.
Fire Incidents with I-Joists
Specific fire incident reports indicate that when directly exposed to fire (unprotected), the loss of strength of I-joists often occurs in conjunction with burn-through of floor sheathing. Within the I-joist itself, the web is consumed first (because of reduced mass). Once the web is consumed, the bottom flange is no longer attached to the joist and falls from the system. Numerous fire incidents have been reported where the only remaining structural components in the floor system were the top flange and floor sheathing. The resulting floor systems, while remaining intact, had over 12" of deflection. Similarly, many reports indicate that firefighters either felt a floor become "soft" or "spongy" or visually observed deflection and exited the structure.