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Fireresistance Rating of Concrete Masonry Assembliesc
Minimum required equivalent thickness
of the concrete masonry assemblya (inches).
Aggregate type in the
concrete masonry unitb |
Fireresistance Rating (hours) |
| 4 |
3 |
2 |
1 |
1 |
.75 |
.50 |
|
| Calcareous or siliceous gravel |
6.2 |
5.3 |
4.2 |
3.6 |
2.8 |
2.4 |
2.0 |
| Limestone Cinders or slag |
5.9 |
5.0 |
4.0 |
3.4 |
2.7 |
2.3 |
1.9 |
| Expanded clay shale or slate |
5.1 |
4.4 |
3.6 |
3.3 |
2.6 |
2.2 |
1.8 |
| Expanded slag or pumice |
4.7 |
4.0 |
3.2 |
2.7 |
2.1 |
1.9 |
1.5 |
Note a. Fireresistance rating between the hourly fireresistance rating periods listed shall be determined by linear interpolation based on the equivalent thickness value of the concrete masonry assembly.
Note b. Minimum required equivalent thickness corresponding to the hourly fireresistance rating for units made with a combination of aggregates shall be determined by linear interpolation based on the percent by volume of each aggregate used in the manufacture.
Note c. 1 inch = 25.4 mm.
• Due to the complexity of equivalent thickness measurements and different weight classifications of block available, we encourage you to call a masonry supply dealer or manufacturer to obtain the current fire rating.
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