What is the maximum area allowed for draft stops provided between a suspended ceiling and the floor above?

Concealed horizontal spaces, such as the plenum created between a suspended ceiling and the floor or roof deck above, must be subdivided by draft stops to limit the spread of fire and smoke. According to NFPA 101, Life Safety Code, these concealed horizontal spaces must be draftstopped so that the maximum area of any single subdivided space does not exceed 1,000 ft² (93 m²). This compartmentation is a critical passive fire protection feature that prevents the unimpeded travel of combustion products through hidden building pathways, allowing more time for occupant egress and firefighting operations.

A. 500 ft² (46 m²): This area is smaller than the maximum limit specified by the code for draftstopping in horizontal concealed spaces.

C. 1,500 ft² (140 m²): This value is not a standard code requirement for draft stop area limitations in floor-ceiling assemblies.

D. 3,000 ft² (280 m²): This larger area limitation is typically associated with draftstopping in attic spaces of combustible construction, not the concealed space within a floor-ceiling assembly.

1. NFPA 101®, Life Safety Code®, 2021 Edition.

Section 8.15.4.3: "Concealed horizontal spaces shall be draftstopped so that the maximum area of any such space does not exceed 1000 ft² (93 m²)."

2. Cote, A. E., & Harrington, G. P. (Eds.). (2008). Fire Protection Handbook (20th ed.). National Fire Protection Association.

Volume I, Section 6, Chapter 7, "Confining Fires in Buildings": This chapter discusses the principles of compartmentation, including the use of draft stops in concealed spaces. It explains that codes, such as NFPA 101, limit the area of concealed spaces like those above suspended ceilings to 1000 ft² to prevent rapid fire spread. (Specific discussion found in the subsection on "Draftstopping").

3. Meacham, B. J. (2016). SFPE Handbook of Fire Protection Engineering (5th ed.). Springer.

Chapter 52, "Analysis of Fire Brigades and Fire-Fighting Operations": This chapter references building code requirements for compartmentation as a fundamental element affecting firefighting strategy. It notes that limitations on concealed space areas, such as the 1000 ft² rule for floor-ceiling plenums, are designed to contain a fire to a manageable area in its early stages. (DOI: https://doi.org/10.1007/978-1-4939-2562-452)