Type IV construction typically uses heavy timbers such as can be seen in many rustic restaurants, churches, barns, old factories, and historic structures.

Barns used as agricultural buildings are required to comply with NEC^® Article 547 (if supplied with an electrical system). These types of buildings are often associated with other farming type processes such as grain processing.

When a building is used for grain processing or packaging and distributing farm animal feed, it might be considered a Class II hazardous location and be subject to the wiring methods required in NEC^® Article 502.

NEC Article 502 provides requirements for electrical and electronic equipment and wiring for all voltages in Class II, Division 1 and 2 locations where fire or explosion hazards may exist due to combustible dust.

Old factories are often Type IV construction, and many fall under the category of a hazardous classified location in accordance with NEC^® Article 503.

NEC Article 503 covers Class III hazardous locations where nonmetal combustible fibers/flyings are in the air under normal operating conditions in quantities sufficient to produce explosible mixtures or where mechanical failure or abnormal operation of machinery or equipment might cause combustible fibers/flyings to be produced and might also provide a source of ignition through simultaneous failure of electrical equipment, through operation of protection devices, or from other causes.

Such locations can include rayon, cotton, and other textile mills; associated manufacturing and processing plants; cotton gins and cotton-seed mills; flax-processing plants; clothing manufacturing plants; woodworking plants; and establishments and industries involving similar hazardous processes or conditions.

Ignitible fibers/flyings can include rayon, cotton (including cotton linters and cotton waste), sisal or henequen, istle, jute, hemp, tow, cocoa fiber, oakum, baled waste kapok, Spanish moss, excelsior, and other materials of similar nature.

IBC Section 602.4 specifies that Type IV construction is a type of construction in which the building elements are mass timber or noncombustible materials and have fire-resistance ratings in accordance with Table 601.

Section 602.4.1.5 states that concealed spaces shall not contain combustibles other than electrical, mechanical, fire protection, or plumbing materials and equipment permitted in plenums in accordance with Section 602 of the International Mechanical Code.