Load Duration

The load duration factor stems from the fact that wood is strongest when loaded for a short time. Design properties are typically based on the assumption that the load will be on the structure for a "normal" period of time. Some loads such as wind loads do not occur at full intensity except for a relatively short period of time. Since the duration of the wind load is shorter than the assumed basis for normal design values, some design properties may be increased by a duration factor. Typical load duration factors are noted below:

• 100% (IBC, NBC) Floor Live Load

• 115% (IBC) or 100% (NBC) Roof Snow Load

• 125% (IBC) Roof Construction Live Load

• 160% (IBC) or 115% (NBC) Wind or Quake Live Load