Fire Resistive Ratings
(Excerpted from Fire Resistive Construction Using Concrete Masonry and Design of Reinforced Masonry Structures, published by CMACN [with updated references to current building code])
Concrete masonry is a preferred material for use in constructing fire-resistive walls. It is a multi-functional system in a single package:
- Noncombustible, stable in response to fire
- Structurally sound; exceptional seismic performance
- Durable, long-lasting with low life-cycle costs
- The fire-resistance ratings of the various thicknesses of concrete masonry walls are based on 2010 CBC Table 720.1(2), Rated Fire-resistance Periods for Various Walls and Partitions, Item Numbers 3-1.1 through 3-1.4. Equivalent thicknesses are defined in 2010 CBC Section 721.3.1
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For partially grouted concrete masonry walls using 8-inch thick cmu rated at 2 hours, the fire-resistance rating can be increased to 4 hours when ungrouted cores are filled with any of the following:
- Silicone-treated perlite loose-fill insulation conforming to ASTM C 549.
- Vermiculite loose-fill insulation conforming to ASTM C 516. Expanded clay, shale, or slate lightweight aggregate conforming to ASTM C 331.
- Sand of slag having a maximum particle size of 3/8 inch, and conforming to ASTM C 33.
- A special 8-inch cmu with minimum 2 1/4-inch thick face shells may be available. Consult your representative.
- The calculated equivalent thickness of a concrete masonry wall may include the thickness of applied plaster and lath, gypsum wallboard, or 1.5 times the thickness of gypsum plaster applied per CBC Chapter 25.
- Determine the fire-resistance rating of walls with cmu using blended aggregates per 2010 CBC Section 721.3.1 and ACI 216.1/TMS 0216 [upon which Section 721.3.1 is based].
| FIRE RATINGS OF CONCRETE MASONRY WALLS EXPANDED CLAY, SHALE OR SLATE AGGREGATES |
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| Width (W) | Fire Resistance Ratings | ||
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| Nominal | Specified | Partial Grouted or Hollow Masonry | Solid Grouted Masonry |
| 4" | 3 5/8" | Less Than 1 Hour | 2 Hours |
| 6" | 5 5/8" | 1 Hour | 4 Hours |
| 8" | 7 5/8" | 2 Hour | 4 Hours |
| 10" | 9 5/8" | 2 Hour | 4 Hours |
| 12" | 11 5/8" | 3 Hour | 4 Hours |
| FIRE RATINGS OF CONCRETE MASONRY WALLS LIMESTONE, CINDERS OR AIR-COOLED SLAG AGGREGATES |
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| Width (W) | Fire Resistance Ratings | ||
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| Nominal | Specified | Partial Grouted or Hollow Masonry | Solid Grouted Masonry |
| 4" | 3 5/8" | Less Than 1 Hour | 1 Hour |
| 6" | 5 5/8" | 1 Hour | 3 Hours |
| 8" | 7 5/8" | 1 Hour | 4 Hours |
| 10" | 9 5/8" | 2 Hour | 4 Hours |
| 12" | 11 5/8" | 3 Hour | 4 Hours |
| FIRE RATINGS OF CONCRETE MASONRY WALLS CALCAREOUS OR SILICEOUS AGGREGATES |
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| Width (W) | Fire Resistance Ratings | ||
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| Nominal | Specified | Partial Grouted or Hollow Masonry | Solid Grouted Masonry |
| 4" | 3 5/8" | Less Than 1 Hour | 1 Hour |
| 6" | 5 5/8" | 1 Hour | 3 Hours |
| 8" | 7 5/8" | 1 Hour | 4 Hours |
| 10" | 9 5/8" | 2 Hours | 4 Hours |
| 12" | 11 5/8" | 2 Hour | 4 Hours |
Angelus Block Co., Inc. supplies this information as an educational aid in understanding the benefits of concrete masonry construction and our products. It is the responsibility of the user to obtain engineering or other advisory services from licensed professionals as the basis for incorporating into any project any information, detail, or product offered herein.