2021 IBC Chapter 7
Chapter 7 is where construction type turns into physical walls, floors and doors that hold back fire and smoke. Four wall types do most of the work, and they are easy to mix up: fire walls, fire barriers, fire partitions and smoke barriers. Each has its own purpose, rating and continuity rule. This lesson also covers the rated doors, exterior wall openings and penetrations that make or break those walls in the field. Local adoption governs the edition and any amendments.
A fire-resistance rating belongs to a tested assembly, the whole wall or floor with its framing, board, joints and fasteners, not to a single material. The second half of the rule is continuity. Each wall type below has its own continuity section, and they follow a pattern: from the top of the foundation, or the floor or ceiling below, to the underside of the floor or roof sheathing, deck or slab above, including through concealed spaces. A frequent finding is a rated wall that quietly stops at a lay-in ceiling.
A fire wall divides one building into separate buildings for height, area and construction purposes, which is why the definition of building area names both exterior walls and fire walls. Table 706.4 sets the rating by group: 4 hours for H-1 and H-2; 3 hours for A, B, E, H-4, I, R-1, R-2 and U, and also for F-1, H-3, H-5, M and S-1; and 2 hours for F-2, S-2, R-3 and R-4. In the first 3-hour row, Type II or V construction may use 2 hours. A fire wall runs from exterior wall to exterior wall and extends at least 18 inches beyond the exterior surface, with exceptions (706.5). Vertically it runs from the foundation to at least 30 inches above both adjacent roofs (706.6). Limited exceptions allow it to stop at the underside of the roof deck, for example a 2-hour wall with a 1-hour lower roof within 4 feet, no roof openings within 4 feet, and at least Class B roof coverings on both buildings.
A fire barrier is a rated wall (or a horizontal assembly under Section 711) that separates parts of the same building. Section 707.3 sends each use to its home section: shafts (713.4), interior exit stairways (1023.2), exit passageways, horizontal exits, atriums (404.6, 1 hour), incidental uses (Table 509.1), control areas, separated occupancies (Table 508.4) and fire areas. Fire areas use Table 707.3.10: 4 hours for H-1 and H-2; 3 hours for F-1, H-3 and S-1; 2 hours for A, B, E, F-2, H-4, H-5, I, M, R and S-2; 1 hour for U, with mixed fire areas taking the highest value. Shafts and interior exit stairways share one rule: 2 hours when they connect four stories or more, 1 hour when they connect fewer than four. Count basements but not mezzanines. The rating is never less than the floor assembly penetrated, and it need not exceed 2 hours.
Fire partitions are the lighter walls: dwelling and sleeping unit separations, corridor walls, mall tenant walls, elevator lobbies and similar. The base rating is 1 hour (708.3), with two exceptions for 1/2 hour: corridor walls where Table 1020.2 allows it, and dwelling or sleeping unit separations in Types IIB, IIIB and VB when the building is sprinklered throughout under 903.3.1.1. A fire partition may end at a rated floor/ceiling assembly whose rating is not less than the partition (708.4).
Smoke barriers exist to stop smoke, and they carry a 1-hour rating (the exception is 0.10-inch steel in Group I-3). They must be continuous from the floor below to the deck above, through concealed spaces (709.4). Group I-1 Condition 2 is one place you meet them, where compartments are limited to 22,500 square feet (420.6). Keep the four straight: fire walls make separate buildings, fire barriers separate parts of one building, fire partitions are the lighter version, and smoke barriers block smoke between compartments.
Table 716.1(2) matches the door to the wall. Two 1-1/2 hour doors on opposite sides of one opening in a fire wall count as one 3-hour door. Fire-protection-rated windows are not allowed in fire walls or in fire barriers rated over 1 hour, though tested fire-resistance-rated glazing can be used there. Table 716.1(3) covers other walls.
| Wall | Minimum door |
|---|---|
| Fire wall, 3 hr | 3 hr |
| 2 hr shaft or interior exit stair enclosure | 1-1/2 hr |
| 1 hr shaft, exit stair or exit passageway enclosure | 1 hr |
| Other 1 hr fire barrier; other 1 hr fire partition | 3/4 hr |
| Corridor wall, 1 hr or 1/2 hr; 1 hr smoke barrier | 20 minutes |
Table 705.8 limits openings as a percent of the exterior wall area per story, by fire separation distance. Protected openings use assemblies under Section 716.
| FSD | Unprotected, nonsprinklered | Unprotected, sprinklered | Protected |
|---|---|---|---|
| 0 to under 3 ft | Not permitted | Not permitted | Not permitted |
| 3 to under 5 ft | Not permitted | 15% | 15% |
| 5 to under 10 ft | 10% | 25% | 25% |
| 10 to under 15 ft | 15% | 45% | 45% |
| 15 to under 20 ft | 25% | 75% | 75% |
| 20 to under 25 ft | 45% | No limit | No limit |
| 25 to under 30 ft | 70% | No limit | No limit |
| 30 ft or more | No limit | No limit | No limit |
Worked example: a sprinklered Group B wall is 100 feet long and 20 feet high, so its area per story is 2,000 square feet, and it sits 12 feet from the lot line. The 10 to under 15 foot row allows 45 percent unprotected, so 0.45 x 2,000 = 900 square feet of openings. If the building were nonsprinklered, the same row allows 15 percent, or 300 square feet.
Section 714 covers pipes, conduit and cables through rated walls and floors. A through penetration is protected by an approved firestop system tested under ASTM E814 or UL 1479, with an F rating not less than the wall's rating. In a floor or other horizontal assembly the system also needs a T rating of at least 1 hour and not less than the floor's rating, with narrow exceptions such as drains in the concealed floor space. The T rating does not apply to walls unless another section asks for it. Membrane penetrations, such as steel electrical boxes, have their own limits in 714.4.2. Joints where rated assemblies meet are Section 715. Firestopping is inspected before it is concealed (110.3.8).
Fireblocking (718.2) stops fire in concealed wall spaces at the ceiling and floor and at intervals of no more than 10 feet horizontally, and around pipes and vents at floor and ceiling levels. Draftstopping subdivides combustible floor/ceiling assemblies so that no area exceeds 1,000 square feet, and attics and concealed roof spaces so that none exceeds 3,000 square feet. These limits are for occupancies other than Group R, and they do not apply where the building is sprinklered under 903.3.1.1.
In the field
On a tenant build-out inspection, the framing looks right at eye level, but above the ceiling grid the corridor partition stops at the tile line with no rated ceiling assembly above it, a plumber has run a pipe through it with no firestop, and an electrical box sits back to back with one on the other side. Follow every rated wall up to the deck above, check the assembly label or design number, and look for a firestop system at every penetration. All of it has to be seen before the ceiling closes.
1. Under Table 706.4, the fire wall rating for a Group M building is:
2. Section 706.6 requires a fire wall to extend from the foundation to a point above both adjacent roofs of at least:
3. A fire wall must extend horizontally beyond the exterior surface of the exterior walls by at least:
4. An inspector reviews a fire wall in a Group R-2 building of Type VA construction. Table 706.4 normally requires 3 hours. What is the lowest rating permitted for this type?
5. An inspector is checking the enclosure of an elevator shaft that connects four stories above grade. The minimum rating of the shaft enclosure is:
6. A shaft enclosure connects three stories above grade, with no basement. The minimum rating, ignoring any higher floor rating, is:
7. The base fire-resistance rating for a fire partition under Section 708.3 is:
8. Dwelling unit separations in a Group R-2 building of Type IIIB construction sprinklered throughout under 903.3.1.1 may be rated:
9. Under Section 709.3, a smoke barrier must have a fire-resistance rating of:
10. An inspector is checking a door in the 2-hour enclosure of an interior exit stairway. The minimum fire door assembly rating is:
11. The minimum door rating for a 1-hour corridor wall that is a fire partition is:
12. An inspector reviews a sprinklered Group B building with a wall 100 feet long and 20 feet high, 12 feet from the lot line. Using Table 705.8, the maximum area of unprotected openings is:
13. A pipe penetrates a floor assembly that is required to be 2 hours. The firestop system must have:
14. Fireblocking in concealed stud wall spaces is required at ceiling and floor levels and at horizontal intervals of no more than: