Structural systems in wood can be divided into wood-frame and heavy timber construction. The fire resistance and minimum sizes of structural components in heavy timber construction is discussed under the section on Heavy Timber Construction.

These two types of construction have important differences. They relate to:

• the size of the wood members
• the methods of assembly
• the degree to which they must be combined with other materials to achieve fire-safe conditions

The type of construction permitted, wood-frame, heavy timber of non-combustible depends on building size and use. Buildings are typically classified according to occupancy, building height and area.

Though the structure of a modern wood-frame building may be made entirely of wood, protective finishes such as gypsum wallboard can be applied to the framing to provide structural fire resistance where required.

Wood-frame assemblies can economically be made to resist the effects of a fire for up to two hours through the use of appropriate materials and construction methods. Experience has proven this construction system to be reliable and safe. Various configurations of wood frame floor and wall assemblies have been tested and based on the test results, have been assigned varying degrees of fire resistance from 45 minutes to two hours.

The following section on Fire Resistance Ratings provides specific information and construction details on wood frame wall assemblies that are assigned various fire resistance ratings. Additional information is listed in the NBCC.