Final answer:
The IRC code requires draftstopping in all ceiling and floor openings larger than 1000 square feet. This technique is used to prevent the movement of air and consequently, the spread of fire and smoke.
Step-by-step explanation:
According to the International Residential Code (IRC), draftstopping is necessary in floor and ceiling openings that are larger than 1000 square feet (option d). Draftstopping is a technique used in building construction to restrict the movement of air within open spaces in building assemblies. It aids in preventing the spread of fire and smoke through large concealed spaces in the building's structure.
Learn more about Draftstopping