Code of Massachusetts Regulations
780 CMR - STATE BOARD OF BUILDING REGULATIONS AND STANDARDS
Chapter 7 - Fire and Smoke Protection Features
Section 721 - CALCULATED FIRE RESISTANCE
Subsection 721.4 - Clay brick and tile masonry
Current through Register 1531, September 27, 2024
The provisions of this section contain procedures by which the fire-resistance ratings of clay brick and tile masonry are established by calculations.
721.4.1 Masonry walls. The fire-resistance rating of masonry walls shall be based upon the equivalent thickness as calculated in accordance with this section. The calculation shall take into account finishes applied to the wall and airspaces between wythes in multiwythe construction.
TABLE 721.4.1(1) FIRE-RESISTANCE PERIODS OF CLAY MASONRY WALLS
| MATERIAL TYPE | MINIMUM REQUIRED EQUIVALENT THICKNESS FOR FIRE RESISTANCEa, b, c (inches) | |||
| 1 hour | 2 hour | 3 hour | 4 hour | |
| Solid brick of clay or shaled | 2.7 | 3.8 | 4.9 | 6.0 |
| Hollow brick or tile of clay or shale, unfilled | 2.3 | 3.4 | 4.3 | 5.0 |
| Hollow brick or tile of clay or shale, grouted or filled with materials specified in Section 721.4.1.1.3 | 3.0 | 4.4 | 5.5 | 6.6 |
| For SI: 1 inch = 25.4 mm. |
| a. Equivalent thickness as determined from Section 721.4.1.1. |
| b. Calculated fire resistance between the hourly increments listed shall be determined by linear interpolation. |
| c. Where combustible members are framed in the wall, the thickness of solid material between the end of each member and the opposite face of the wall, or between members set in from opposite sides, shall not be less than 93 percent of the thickness shown. |
| d. For units in which the net cross-sectional area of cored brick in any plane parallel to the surface containing the cores is at least 75 percent of the gross cross-sectional area measured in the same plane. |
TABLE 721.4.1(2) FIRE-RESISTANCE RATINGS FOR BEARING STEEL FRAME BRICK VENEER WALLS OR PARTITIONS
| WALL OR PARTITION ASSEMBLY | PLASTER SIDE EXPOSED (hours) | BRICK FACED SIDE EXPOSED (hours) |
| Outside facing of steel studs:
1/2" wood fiberboard
sheathing next to studs,3/4"
airspace formed with 3/4" *
15/8" wood strips placed over
the fiberboard and secured to the studs; metal or wire lath nailed to such strips, 33/4" brick veneer held in place by filling 3/4" airspace between the brick and lath with mortar. Inside facing of studs:3/4"unsanded gypsum plaster on metal or wire lath attached to5/16" wood strips secured to edges of the studs. | 1.5 | 4 |
| Outside facing of steel studs:. 1" insulation board sheathing attached to studs, 1" airspace, and 33/4" brick veneer attached to steel frame with metal ties every 5th course. Inside facing of studs:7/8" sanded gypsum plaster (1:2 mix) applied on metal or wire lath attached directly to the studs. | 1.5 | 4 |
| Same as above except use 7/8" vermiculite-gypsum plaster or 1" sanded gypsum plaster (1:2 mix) applied to metal or wire. | 2 | 4 |
| Outside facing of steel studs: 1/2" gypsum sheathing board, attached to studs, and 33/4" brick veneer attached to steel frame with metal ties every 5th course. Inside facing of studs:1/2" sanded gypsum plaster (1:2 mix) applied to 1/2" perforated gypsum lath securely attached to studs and having strips of metal lath 3 inches wide applied to all horizontal joints of gypsum lath. | 2 | 4 |
| For SI: 1 inch = 25.4 mm. |
TABLE 721.4.1(3) VALUES OF Rn 0.59
| Rn0.59 | R (hours) |
| 1 | 1.0 |
| 2 | 1.50 |
| 3 | 1.91 |
| 4 | 2.27 |
TABLE 721.4.1(4) COEFFICIENTS FOR PLASTER, pl a
| THICKNESS OF PLASTER (inch) | ONE SIDE | TWO SIDE |
| 1/2 | 0.3 | 0.6 |
| 5/8 | 0.37 | 0.75 |
| 3/4 | 0.45 | 0.90 |
| For SI: 1 inch = 25.4 mm. |
| a. Values listed in table are for 1:3 sanded gypsum plaster. |
TABLE 721.4.1(5) REINFORCED MASONRY LINTELS
| NOMINAL LINTEL WIDTH (inches) | MINIMUM LONGITUDINAL REINFORCEMENT COVER FOR FIRE RESISTANCE (inch) | |||
| 1 hour | 2 hour | 3 hour | 4 hour | |
| 6 | 11/2 | 2 | NP | NP |
| 8 | 11/2 | 11/2 | 13/4 | 3 |
| 10 or more | 11/2 | 11/2 | 11/2 | 13/4 |
| For SI: 1 inch = 25.4 mm. |
| NP = Not permitted. |
TABLE 721.4.1(6) REINFORCED CLAY MASONRY COLUMNS
| COLUMN SIZE | FIRE-RESISTANCE RATING (hour) | |||
| 1 | 2 | 3 | 4 | |
| Minimum column dimension (inches) | 8 | 10 | 12 | 14 |
| For SI: 1 inch = 25.4 mm. |
| Te = Vn /LH | (Equation 7-8) |
where:
Te = The equivalent thickness of the clay masonry unit (inches).
Vn = The net volume of the clay masonry unit (inch3).
L = The specified length of the clay masonry unit (inches).
H = The specified height of the clay masonry unit (inches).
| R = (Rn0.59 + pl)1.7 | (Equation 7-9) |
where:
R = The fire-resistance rating of the assembly (hours).
Rn=The fire-resistance rating of the individual wall (hours).
pl = Coefficient for thickness of plaster.
Values for Rn0.59 for use in Equation 7-9 are given in Table 721.4.1(3). Coefficients for thickness of plaster shall be selected from Table 721.4.1(4) based on the actual thickness of plaster applied to the wall or partition and whether one or two sides of the wall are plastered.
| R = (R 10.59 + R 20.59 + ...+Rn0.59 + as)1.7 | (Equation 7-10) |
where:
R = The fire-resistance rating of the assembly (hours).
R1, R2 and Rn = The fire-resistance rating of the individual wythes (hours).
as = Coefficient for continuous airspace.
Values for Rn0.59 for use in Equation 7-10 are given in Table 721.4.1(3). The coefficient for each continuous airspace of 1/2 inch to 31/2 inches (12.7 to 89 mm) separating two individual wythes shall be 0.3.
Exception: For exterior walls with a fire separation distance greater than 5 feet (1524 mm), the fire shall be assumed to occur on the interior side only.
721.4.2 Multiwythe walls. The fire-resistance rating for walls or partitions consisting of two or more dissimilar wythes shall be permitted to be determined by the formula:
| R = (R 10.59 + R 20.59 + ...+Rn0.59)1.7 | (Equation 7-11) |
where:
R = The fire-resistance rating of the assembly (hours).
R 1, R 2 and Rn = The fire-resistance rating of the individual wythes (hours).
Values for Rn0.59 for use in Equation 7-11 are given in Table 721.4.1(3).
721.4.3 Reinforced clay masonry lintels. Fire-resistance ratings for clay masonry lintels shall be determined based on the nominal width of the lintel and the minimum covering for the longitudinal reinforcement in accordance with Table 721.4.1(5).
721.4.4 Reinforced clay masonry columns. The fire-resistance ratings shall be determined based on the last plan dimension of the column in accordance with Table 721.4.1(6). The minimum cover for longitudinal reinforcement shall be 2 inches (51 mm).
