Fire Resistive Ratings
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
No toxic gases released when heated
Durable, long-lasting, with low life-cycle costs
The fire-resistance ratings of the various thicknesses of concrete masonry walls are based on 2019 CBC Table 721.1(2), Rated Fire-resistance Periods for Various Walls and Partitions, Item Numbers 3-1.1 through 3-1.4:
3-1.1 Expanded slag or pumice
3-1.2 Expanded clay, shale or slate
3-1.3 Limestone, cinders or air-cooled slag
3-1.4 Calcareous or siliceous gravel
| Partial Grouted | Solid Grouted1 | ||||||
|---|---|---|---|---|---|---|---|
| CMU ASTM C90 Wt. Classification | NW | MW | LW | NW | MW | LW | |
Nominal Width |
4 | <1 Hour | <1 Hour | 1 Hour |
1 Hour |
1 Hour |
1 Hour |
| 6 | 1 Hour |
1 Hour |
1 Hour |
3 Hours |
3 Hours |
3 - 4 Hours2 |
|
| 8 | 1 Hour |
1 Hour |
2 Hours |
4 Hours |
4 Hours |
4 Hours |
|
| 10 | 2 Hours |
2 Hours |
2 Hours |
4 Hours |
4 Hours |
4 Hours |
|
| 12 | 2 Hours |
2 Hours |
2 - 3 Hours2 |
4 Hours |
4 Hours |
4 Hours |
|
|
1 4-inch wide cmu are solid units in lieu of solid grouted. |
|||||||
Equivalent thicknesses are defined in 2019 CBC Section 722.3.1.
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.
The calculated equivalent thickness of a concrete masonry wall may include the thickness of applied plaster and lath, gypsum wallboard, or gypsum plaster.
The fire-resistance rating of walls with cmu using blended aggregates is determined per 2019 CBC Section 722.3.1 and ACI 216.1/TMS 0216 [upon which Section 722.3.1 is based].
Download the Masonry Fire-Resistance-Rated Construction Code References. The document highlights code sections related to masonry and fire-resistance.
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.
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