Jon Nisja, Data and Fire Protection Specialist

Ceilings play a significant role in effective fire sprinkler operation. The materials used to construct the ceiling also factor into correct sprinkler placement and effective operation. This blog will examine the role that the combustibility of ceiling materials plays in determining sprinkler location and protection limits.

Combustible or Noncombustible

Previous NFSA blogs have explained the differences between combustible and noncombustible. While the technical definitions get a little confusing, there are some commonsense applications.

Combustible means that the material can ignite and burn and includes items such as wood, paper, and plastics. For the purposes of determining ceiling types, we are basically dealing with wood. If the exposed ceiling members – either structural or finishes – are wood, it means the ceiling is combustible.

Here are some examples of combustible ceilings:

Figure 1 – Combustible Ceiling Having Wood Beams and Wood Finish Materials

Figure 2 – Combustible Ceiling Having Hybrid Wood and Steel Trusses and Plywood Decking

Noncombustible means that the material will not ignite, burn, or release flammable vapors when exposed to fire or heat. For purposes of determining ceiling types, exposed ceiling materials such as steel, concrete, plaster, gypsum, or acoustic ceiling tile would be considered noncombustible.

The following photos show examples of common noncombustible ceilings.

Figure 3 – Noncombustible Ceiling Having Gypsum Surfaces

Figure 4 – Noncombustible Ceiling Constructed of Concrete Beams

Figure 5 – Noncombustible Ceiling Using Steel Bar Joists and Metal Decking

Impact on Fire Sprinklers

With combustible ceilings, it is possible that the materials could ignite and contribute to the fire. With noncombustible ceilings, it is far less likely that these materials will become involved in the fire – at least during the initial phases before sprinklers would operate. NFPA 13 allows a larger protection area per sprinkler when the ceiling is noncombustible. For example, NFPA 13 allows standard spray pendent or upright sprinklers in light hazard occupancies to protect up to 225 sq. ft. for noncombustible obstructed or unobstructed ceiling configurations. This maximum protection area can be as low as 130 sq. ft. for combustible obstructed ceiling configurations [see NFPA 13 – 2025 edition – Table 10.2.4.2.1(a)].

Summary

The combustibility or the ceiling (or roof) materials play a role in proper fire sprinkler spacing. Various types of combustible and noncombustible ceilings were identified and sprinkler protection was addressed

If the ceiling (or roof) materials can burn, NFPA 13 often limits the protection area for sprinklers since they potentially add to the fuel load. Ceilings or roofs of noncombustible spacing typically allow much greater spacing as they don’t contribute to the fuel load.

Jon Nisja has been a Data and Fire Protection Specialist with the National Fire Sprinkler Association (NFSA). He began his fire service career as a firefighter in November of 1978. Jon served as a fire marshal in two communities since 1985 and as a state fire safety supervisor for the Minnesota State Fire Marshal Division. From 2005-2022, he supervised the State Fire Marshal’s fire protection, training, and data teams. He is the past president of both the Fire Marshals Association of Minnesota and the International Fire Marshals Association. He retired at the end of a 43-plus year fire service career in 2022 and was hired by NFSA. Jon can be contacted at nisja@nfsa.org.